: Headgasket replace



haymaker
09-21-04, 12:21 AM
Has anyone successfully replaced the head gasket on a Northstar without timeserting the block? I mean hands on replacement not a secondhand story.

Spyder
09-21-04, 01:02 AM
If the heads come off, you MUST timesert it. No question.

growe3
09-21-04, 08:34 AM
I have done the head gasket repair on both of my 93' STS's.

In both cases several holes had "soft" threads in them, which I believe allowed the head gaskets to start leaking, and a couple of head bolts on each engine actually pulled the threads out when I remove them.

Do not try to replace the head gaskets without TimeSerting all 20 head bolt holes.

I would also advise using only OEM gaskets for this engine. The head gaskets are special graphite composition and come with the required treated replacement bolts. Most of the other gaskets are steel shim with double silicone beads on them, or shaped silicone strips.

Note:
This is a major labor job; not a hang over the fender and get it done in an afternoon job.

The engine must be removed from the car to do the job. It can be removed from the top or bottom; I prefer the top.

Read up and be prepared for this or have an experienced Cadillac Northstar engine mechanic do the work. Shops charge $2,000 to $4,500 for this repair for good reason.
The parts are about $600 the rest is labor.

-George

haymaker
09-21-04, 10:05 PM
I have done the head gasket repair on both of my 93' STS's.

In both cases several holes had "soft" threads in them, which I believe allowed the head gaskets to start leaking, and a couple of head bolts on each engine actually pulled the threads out when I remove them.

Do not try to replace the head gaskets without TimeSerting all 20 head bolt holes.

I would also advise using only OEM gaskets for this engine. The head gaskets are special graphite composition and come with the required treated replacement bolts. Most of the other gaskets are steel shim with double silicone beads on them, or shaped silicone strips.

Note:
This is a major labor job; not a hang over the fender and get it done in an afternoon job.

The engine must be removed from the car to do the job. It can be removed from the top or bottom; I prefer the top.

Read up and be prepared for this or have an experienced Cadillac Northstar engine mechanic do the work. Shops charge $2,000 to $4,500 for this repair for good reason.
The parts are about $600 the rest is labor.

-George
Growe3. I already finished the timesert installation two days ago. My 97 SLS has 77,000 miles. It has been leaking for about two years, not much at first but it can only be driven for a few miles before it overheats lately. This is what I found when I pulled it apart. Number one headbolt on the right bank came out with less than ten lbs ft of torque. The threads in that hole were ok or at least the bolt for the timesert plate tightened ok. That bolt was covered in oil. Threads came out with four bolts. Two bolts between cylinders two and four one bolt at the bottom between four and six and the other at bottom left of cylinder two. All the bolt holes that had given up their threads had a very bad smell and were coated with I guess cooked Dex-cool.

On the left bank the number seven head bolt was about the same as number one head bolt on the right bank (came aout real easy and was coated in oil). The threads came out with two bolts bottom right cylinder one and upper between cylinders one and three. The remaining seven on this side gave out a load crack as I broke them loose.
I looked over the head gaskets. They don't have the normal easy to find markings of a blown head gasket. I can usually spot the leak at the head gasket and block or head surface as soon as I pull the head on a cast iron engine. On the Northstar it took me a few minutes. I found the leak at the cylinder deck surface first then I knew where to look on the gasket. It was between cylinders two and four. I have pulled the threads out of the block tightening head bolts on cast iron engines a few times but at most one bolt per many engines. This time I repair all the head bolt threads on one engine. Pulling the engine out of the car is the hard part. Working on the engine is a pleasure. Open it up and it looks like a fine watch.

Anyway before I started working on it I asked the dealer the price for the repair. He stated $33,00.00 and would not stand behind. The only way he would stand behind the work was if he replaced the engine with a new crate engine from GM seven to eight grand. Car is only worth maybe seven to eight grand so what the hay I wasn't doing anything important anyway.

I put the question about the head gasket replacment out there in hopes of finding at least one person that had successfully completed the task with out timeserts and if so how long did the repair last.

Have you seen the latest price of the timesert kit?

Thanks for the reply..

growe3
09-21-04, 11:55 PM
Have you seen the latest price of the timesert kit?

Thanks for the reply..

My kit cost $326 which included the extra ten Timeserts need to do the complete job.

I bought it from www.timesert.com a couple of years ago.
-George

haymaker
09-22-04, 12:20 AM
My kit cost $326 which included the extra ten Timeserts need to do the complete job.

I bought it from www.timesert.com a couple of years ago.
-George
I checked around for a used kit online before I started. Nothing on line at the time as per used. The only one I could find was $470.00 in town (Columbus Ohio), $519.00 west coast. That was with 10 timeserts in the kit, 10 extra at $2.80 a piece. Looks like a little corner on the market to me.

Kerry97
09-23-04, 04:08 PM
I need to install time-serts in my block after a blown head gasket.
Anyone have a kit they want to sell or even rent to me??
I only expect to do this once in my lifetime.

Dooman
09-29-04, 04:57 PM
I just had it all done.. local shop. 99 STS and it hurts. $3600 with brakes too..

sts96
09-29-04, 07:47 PM
had a blown head gasket on left(front) side, removed engine time-serted all head bolt holes only left were bad.
4601 miles later the block split open just at the bottom of time-serts from front to back on left side. yes followed all instructions to the letter. my guess some blocks are too brittle to repair. replaced entire engine if i have to do this again think i will switch to velcro insted or bolts at least would be easier to take apart LOL sts96

haymaker
09-30-04, 01:14 AM
had a blown head gasket on left(front) side, removed engine time-serted all head bolt holes only left were bad.
4601 miles later the block split open just at the bottom of time-serts from front to back on left side. yes followed all instructions to the letter. my guess some blocks are too brittle to repair. replaced entire engine if i have to do this again think i will switch to velcro insted or bolts at least would be easier to take apart LOL sts96
Sts96. Did the crack go all the way across, front to back, intake to exhaust? Sorry to hear about your Northstar problems.

I would like to compare your teardown to mine.
Did you find any oily bolts? If so, was it or were they next to the problem cylinders? For an example, Cylinders 1-3 were pushing combustion gases into the cooling system (head gasket blown between cylinders 1-3) the oily bolt would be between cylinders 3-5. If you had this oily bolt(s) while you were time-serting did you notice that the threads in that oily hole held the time-sert bolt just fine. In other words the threads were just fine and not stripped (came out on the head-bolt as it was removed from the block). Do you remember if two or more head bolts at or around the problem cylinders carried the threads from the block as they were removed? Did the head gasket from the problem side look as good as the other side?
I’m just trying to figure this out…..

sts96
09-30-04, 10:15 AM
do not recall if bolts were oily,it was all very messy the bolts around cyl # 2&4 were ok the six bolts around cyl # 6&8 came out with the threads. the lesk was between 6&8 also out thru the front of gasket to the outside of engine. yes it was hard to see the problem looking at the old gasket, the other side of the engine was fine bolt and gasket wise, time-serted anyway. do recall that the drill chips were very granular from the bad side the good side were stringy as normal. will try to post picture i'm still trying to figure this out also.lol sts96

Anthony Cipriano
09-30-04, 12:11 PM
STS96. Could you have run the head bolts into the holes with oil or coolant in the holes on the side that cracked. The only time I have seen a failure like in your picture was from head bolts run into the blind holes with oil in them. The oil hydrostaticallly locks in the blind hole as the bolt goes down and causes the block to crack. The oil or other liquid just has nowhere to go so it blows out the bottom of the head bolt hole leading to a crack. That is another reason that head bolts are supposed to be installed dry (with only the factory coating on them) into a dry clean hole. If the bolts were oiled then possibly the oil drained into the bottom of the hole and may have hydrostatically locked as the bolts were run down causing a crack to propogate.

sts96
09-30-04, 09:31 PM
All head bolt holes were cleaned with solvent and compressed air extension gun as per instructions visually checked each hole to ensure no chips remained, all were clean and dry. installed new oem gaskets and bolts purchased at retail price.
Torqued to revised specs, followed instructions to the letter.
The repairs were made on an engine stand with the engine out of the power train which I removed from my favorite car . I worked on it this way to avoid any compromise in quality.
Hope this helps clarify my slow limited typing.
LOL sts96

haymaker
09-30-04, 11:55 PM
In this picture is the crack about 1"-1 1/2" above the parting line at the crank or is that a casting line? The fact that the engine was back into service for another 4,000+ miles after the repair makes me doubt you caused a problem during the time-serting. This problem looks to be quite the exception to the norm.

Night Wolf
09-30-04, 11:56 PM
OT... but why do the pistons look so bad?

haymaker
10-01-04, 12:11 AM
The pistons looked about the same on mine when I time-serted. Looks like carbon deposits to me. Both sides looked the same on my engine (the problem side and the non-problem side). In other words all the piston tops had the same look (carbon deposits).

Night Wolf
10-01-04, 12:16 AM
hmmm.... they just looked really weird to me... like rust, and then a layer of carbon... I can't even see the indents for the valves.....

maybe I was just picturing them to look like the pistons on my enigne, which are basically new...

http://www.cadillacforums.com/photopost/data/1/427PDR_0278.JPG

haymaker
10-01-04, 12:39 AM
That piston looks to be very low miles, cleaned or having been exposed to moisture (water, dex-cool mix). We used to clean the piston top carbon deposts from big-block Chevys by slowly pouring water into the carb with the engine turning @3,000rpm.

sts96
10-01-04, 09:00 AM
I did not understand your question about the direction of the crack, I said front to rear sorry should have said side to side old habits die hard.
the deposits on the pistons are carbon with a generous coating of dex-cool as the head gasket was released from bolt tension by the crack. found a fracture on the other side of the block tranny end of block about same hight. best guess on my part is expansion of time-serts from the setting set up stress cracks that propigated with heating cooling cycling resulting in falure. encourage all who time-sert to do a dye test on the block in the area of timeserts before reinstalling in the car.as it is quite a bit of work to replace the engine. do love my car even with this problem. LOL sts96

Anthony Cipriano
10-01-04, 11:38 AM
I'd say that the pistons look fine. Just like used pistons look.

sts96. Could the head bolts have been bottoming at the bottom of the timeserts or the bottom of the head bolt holes somehow? Do you still have the cracked block around to look at? Several of us looked at the cracked block in wonder. I've never seen anything like that in all my years working around Northstars. It almost looks like the head bolts bottomed in the holes and forced the block apart where the crack is. Can you look at the bottom of the holes and/or the old head bolts from those holes to tell if there was any contact?

sts96
10-01-04, 03:10 PM
Could not tell if bottomed out by looking, so put a head bolt thru the head and scribed a mark on the bolt turned the bolt down into one of the crack holes it went in easily just over 1/2" past the head scribe mark so looks like plenty of room below the bolt to the bottom of the hole all others checked very close to the same depth with a piece of wire. I do not know the history of this car the vin # checked ok on car-fax it had 102 k miles but the computer had been cleared of history, I purchased it in mar of 2004 ps the crack in person is AWESOM the picture does not do it justice. lol sts 96

haymaker
10-01-04, 08:28 PM
I would like to see a good close-up picture of the problem area of the block.

Did you use the standand or big-sert kit?

sts96
10-01-04, 09:21 PM
Used standard kit, my camera just left for a weeks vacationwill try for a better picture soon. lol sts96

Anthony Cipriano
10-02-04, 10:36 PM
Just for the heck of it, screw some of the outboard head bolts on that side in until they bottom and then apply torque and see if that tends to open the crack up. Since the crack is right at where the bottom of the head bolt holes it seems to be related somehow - especially since I've never seen a block crack like that before.

CadiJeff
10-02-04, 10:53 PM
I was thinking, and the only thing I could come up w/ was that a smaller crack or weak spot in the block was already there prior to the timesert, and when the head was put back on the full comp ratio was too much and it just split it out the rest of the way.

sts96
10-03-04, 04:31 PM
Ran a headbolt in far as i could it would not bottom out in the hole lack of threads on the bolt seemed to stop it first about 1/8 inch from the bottom of the bolt hole. the cost to return the old engine was greater than the core charge so just kept it.so can do any tests we can figure out. Think as time permits I will strip the block clean and do a dye crack test on the other side and compare sides should I section one or two bolt holes on the cracked side ??? Thanks sts96

Anthony Cipriano
10-04-04, 02:38 PM
Something doesn't seem right there. Are you sure the timeserts are completely seated in the hole so that the top thread is flush with the top of the land the threads start at? It sounds like they're too high. Normally, without a head on the engine, you should be able to bottom the head bolts from my recollection.

sts96
10-04-04, 03:03 PM
This engine is my first to time-sert so I had to rely on the directions. The stright answer to your question is I don't know. Will break out the sawsall and cut the block open and post pictures of the results

Anthony Cipriano
10-04-04, 03:55 PM
Before you do that, put some of the bolts in until they bottom/stop on the threads/whatever and then "force" them with a socket to see of they tend to open up the crack. I'm still trying to figure what the root cause of the crack is since I've never seen one before like that or in that area at all. If the head bolt threads were bottoming in the top of the timesert (if they weren't quite deep enough) it could start a crack because the head bolts would have forced the timeserts deeper into the holes possibly into an unthreaded area causing high stress which might have instigated the crack. The fact that the block just has never cracked in that spot before at all, that it happened after the timeserting and that it's cracked right at the timesert depth makes me suspicious of what happened during the timeserting process.

haymaker
10-04-04, 10:12 PM
I have looked at the picture of the crack several times and it just appears too low on the block to be at the bottom of the timeserts. I understand that the angle of the picture may cause distortions as to the actual distance from block-deck down to the crack but it just looks too low. If you still have the install-tool from the kit? You could place the tool at the edge of the block with the depth mark at the top of the block allowing the tool to hang down toward the crack. The bottom of the install tool should be very close if not exactly at the bottom of the installed timesert.
I was going to attach a picture but I guess I don't have that option.

dkozloski
10-04-04, 11:47 PM
What works as good as dye pentrant to find cracks in aluminum engine blocks is to clean the area to be inspected thoroughly with Stoddard solvent, rinse with warm water and blow dry with compressed air. Dust the area lightly with talcum or baby powder and warm gently with a propane torch. The solvent and any oil or crud will ooze out of the crack and be immediately visible. This is the procedure that Pratt & Whitney used for many years.

Anthony Cipriano
10-05-04, 11:28 AM
I have looked at the picture of the crack several times and it just appears too low on the block to be at the bottom of the timeserts. I understand that the angle of the picture may cause distortions as to the actual distance from block-deck down to the crack but it just looks too low. If you still have the install-tool from the kit? You could place the tool at the edge of the block with the depth mark at the top of the block allowing the tool to hang down toward the crack. The bottom of the install tool should be very close if not exactly at the bottom of the installed timesert.
I was going to attach a picture but I guess I don't have that option.


No. The Northstar head bolts are very long and thread into the main web material - not up at the deck surface. The crack is down around the head bolt threads.

sts96
10-05-04, 12:24 PM
OK ran 3 center outside headbolts in then tightened to 50ft lbs yes that did open crack more but left only 2 5/8 in. of bolts exposed I think that the head at 3 in thick would prevent bottoming in the bolt holes. found a crack on the other bank outside wall between cyl 5 & 7 about the same position. Have an idea what happened to this engine is the former owner found the head gasket was leaking. Did not want to spend the money to repair it so just poured water and stopleak in to get by as long as they could. The engine cold weather froze and fractured as the cracks are at the bottom of coolant chamber both sides where it has the least give. time-serting and new gaskets provided the stress for the cracks to thermal cycle and join up with each other. really strong bolts and the serts held very well.My theory any way. I do not think the time-serts are any part of the problem lol sts96

Anthony Cipriano
10-05-04, 02:52 PM
Well, that was the other theory that we were considering. That plain water was in it and that it froze at some point. I never saw one freeze so I have no idea of the failure mode of the block.

Measure the length of the head bolts carefully. They stretch a bit under load so it sounds like it is close. Since torquing the bolts against the timeserts recreates the failure I'd be extremely suspicious of them. Extremely. You are not putting any load on the block since the bolts aren't loaded against the head so if the crack is opening up then the bolts must be creating the force internal to the bolt hole to cause this.

If the block had just froze and cracked then I could see the head bolts opening up the crack IF you were torqueing them down with a head on so that the bolt was pulling upward. But, since you're just torqueing against the interference of the bolt in the hole it must be something in the hole that's causing the stress that opens up the block.

My conclusion from what you've said is that either the timeserts aren't in correctly or the bolt is bottoming in the hole. I would guess that the OD threads for the timesert were not deep enough and that the timesert is therefore not seated deep enough in the block. When you torqued the heads on the bolts bottomed against the threads at the top of the timesert and tried to drive the timesert deeper - tap it's own threads forcefully on the OD. That created sufficient stress to cause the block to crack. Since you nearly perfectly duplicate this when you bottom just the plain bolt and torque it and the crack opens up I am pretty sure this is what happened.

Try torqueing them up again so that the crack opens up, shine a strong light through the crack from the outside and look into the water jackets around each cylinder on that side. See where the light shines in relative to the timesert. Take a picture from this angle if you can.

haymaker
10-05-04, 05:33 PM
No. The Northstar head bolts are very long and thread into the main web material - not up at the deck surface. The crack is down around the head bolt threads.
I understand that the threads are in the lower portion of the block. I just finished timeserting my 97 sls a week ago. What I was trying to express by using the timesert installation tool was the actual distance from the top of the block to the crack in relation to the bottom of the timesert. The installation tool is 2.880" from the bottom of the tool to install alignment mark on that tool. When used to install the timesert you start the sert on the end of the tool then run the tool in until the alignment mark is at the top of the block surface and that would also align the bottoms of both tool and timesert (2.880" down from the top of the block deck).

haymaker
10-05-04, 06:22 PM
OK ran 3 center outside headbolts in then tightened to 50ft lbs yes that did open crack more but left only 2 5/8 in. of bolts exposed I think that the head at 3 in thick would prevent bottoming in the bolt holes. found a crack on the other bank outside wall between cyl 5 & 7 about the same position. Have an idea what happened to this engine is the former owner found the head gasket was leaking. Did not want to spend the money to repair it so just poured water and stopleak in to get by as long as they could. The engine cold weather froze and fractured as the cracks are at the bottom of coolant chamber both sides where it has the least give. time-serting and new gaskets provided the stress for the cracks to thermal cycle and join up with each other. really strong bolts and the serts held very well.My theory any way. I do not think the time-serts are any part of the problem lol sts96
If you used the full time-sert kit and followed all the instructions, they're in right. As far as turning them on down into the block. I don't see that happening. The insert is only about 1 3/32" or so over all and the threads on the bolt are 1 7/8" so if the insert is not installed all the way the bolt should just screw on down through the insert with out causing much stress on anything. When I checked my old headbolts they were screwed about 1 1/16" into the threads of the block. That gives you about 13/16" of unused threads.
That's too bad they let it freeze.

sts96
10-05-04, 07:32 PM
Bolted the head on with a head gasket in place it did indeed open the crack up more. However this block is history.
Bought a used engine from LKQ inc. with 81K miles on it comp. check is good leak test to the cooling is good have put 867 miles on runs out very good. Please excuse me while I change the transmission the just gave totaly out. sad to think what this fine car has been thru. lol sts96

haymaker
10-06-04, 12:48 AM
Question? What procedure was used at the Northstar assembly plant in 1997 to install (tighten) the head bolts? In other words, did a machine torque to 22 lb/ft then 60-60-60 degrees, 180 total or did a warm-blooded human labor at this procedure? Was it a totally different procedure? I am just trying to understand how the task was completed.

Anthony Cipriano
10-06-04, 11:44 PM
In the factory the head bolts are all run down simultaneously by an automatic machine with multiple spindles. There are 13 spindles per side and both heads are torqued at the same time. The automatic "multiple" first runs the bolts down until they they're starting to tighten and then simply torques them to about 120 ft. lb. to "pretension" the joint. This burnishes the head bolt threads in the block and puts stress on them so that the final tensioning will be more uniform. Until the pretensioning step the female threads were brand new from the machining opertions so it's common with aluminum threads to pretension the joint to burnish the new threads. Then the multiple loosens all the bolts about 3 turns. It then torques each bolt to the "torque" figure just like the service procedure and then turns each bolt an additional 180 degrees. The head bolt tightening sequence is important in the field since you can only tighten one bolt at a time and that's also why the angle steps of 60-60-60 are given in sequence to gradually pull the head down evenly. In the factory the head bolts are all pulled down simultaneously so there is no torqueing "sequence" used and the angle step is achieved in one smooth motion.

The whole process of pretensioning, loosening and then correctly tensioning the head bolts takes about 35 seconds in the machine.

The critical thing to achieve in tightening and fastener is to stretch the bolt a certain amount to acheive the clamp load desired. To confirm this, special bolts are loaded into an engine occasionally and then run through the multiple to have them tightened. The special bolts then allow a length measurement done sonically without disturbing the joint to confirm the correc bolt stretch was accomplished.

The production equipment is very sophisticated DC electrically driven spindles that can accurately measure torque and angle in several ways. The motors have incoders for angle, current measurement for torque, torque transducers and they can count motor armature revolutions to verify angle from the encoder. So, there are a variety of checks and cross-checks to make sure the tensioning is done accurately. Plus, even though the bolts are turned to the final angle based on the angle alone the torque to do this is monitored so as to confirm that the angle was correct and that the bolt was taking the anticipated amount of torque to reach the angle. Too little or too much torque while going to angle would signify a bad thread, a bottoming bolt, a damaged bolt, etcetera. so it serves as a good crosscheck to the final angle tensioning step.

Every Northstar engine has it's heads put on at that machine. There's only one and the only way allowed to install a head is to do it automatically at the head bolt multiple. Manual tensioning of the head bolts isn't allowed. The torque and angle and feedback data for every engine produced is stored in a computer system at that machine so the head bolt installation data for any engine can be recalled and referenced if a problem shows up.

You could write a decent sized book on torqueing head bolts in production.

peteski
10-07-04, 12:11 AM
This is why we love Anthony so much! I just feel like I took a personal tour of the N* assembly line! I can even smell all that metal and various lubricants! :coolgleam:

Anthony Cipriano - you rock!
:bouncy: :bouncy: :bouncy:

Peteski
:thumbsup: :thumbsup: :thumbsup:

CadiJeff
10-07-04, 02:12 AM
Absolutely, :worship: if I ever find myself in his neck of the woods, I am going to take Anthony out to lunch in appreciation for all the help he has given me or at least buy him a beer. :drinker
thanks man
:thumbsup:

Spyder
10-07-04, 02:36 AM
I think everyone on here owes him a case of beer...

What is your preference, anyways, Anthony?

growe3
10-07-04, 07:49 AM
Thanks for the excellant read "Anthony Cipriano". As always your inside knowledge is both enlighting and interesting.

I have worked on engines for many years and have wondered how some of the machine and assembly operations were performed.

-George

dkozloski
10-07-04, 11:53 AM
Anthony, there are any number of high strength bolt applications in aircraft that are also tightened for stretch but usually it is something like rod bolts where both ends are accessible and can be measured with an outside mike or a go/nogo gauge. I read an article in Scientific American magazine written by an Australian scientist/engineer that said he had identified so many variables involved in tightening bolts by measuring torque that he thought the process almost worthless. My experience from measuring torque with a dial wrench while tightening bolts for stretch pretty much confirms his findings. Tightening bolts by "torque to yield", measuring stretch sonically, and other result based measuring methods is a great leap forward in my estimation. We just completed a repair on an oil-cooled German diesel engine that even the local dealer didn't want to mess with because they felt unsure of all the wrinkles involving fasteners and tightening. We just tackeled each bolt case by case and made up holding tools and measuring equipment as we went. So far everything seems fine.

Anthony Cipriano
10-07-04, 01:53 PM
Anthony, there are any number of high strength bolt applications in aircraft that are also tightened for stretch but usually it is something like rod bolts where both ends are accessible and can be measured with an outside mike or a go/nogo gauge. I read an article in Scientific American magazine written by an Australian scientist/engineer that said he had identified so many variables involved in tightening bolts by measuring torque that he thought the process almost worthless. My experience from measuring torque with a dial wrench while tightening bolts for stretch pretty much confirms his findings. Tightening bolts by "torque to yield", measuring stretch sonically, and other result based measuring methods is a great leap forward in my estimation. We just completed a repair on an oil-cooled German diesel engine that even the local dealer didn't want to mess with because they felt unsure of all the wrinkles involving fasteners and tightening. We just tackeled each bolt case by case and made up holding tools and measuring equipment as we went. So far everything seems fine.

Yes, you hit the nail right on the head. Installing critical fasteners using torque alone is almost worse than useless. It's misleading in that you think you know what you're doing but you really don't because of all the variables.

That's why the torque angle method is preferred for modern critical fasteners. It's a means of replicating bolt stretch based on the pitch of the threads. In it's most fundamental form torque angle allows one to correlate a certain amount of bolt stretch to the thread pitch and allow a specification to be set, based on an angle to turn the bolt, that will stretch it the desired amount. The conclusion is then, that the stretch will be correct thus the clamp load will be correct regardless of the torque that it takes to achieve this.

The torque angle method is not infallible ie. if the threads start to strip as the "angle" is dialed in then the bolt will lose tension and the joint will fail. So, it too, has to be done carefully and if the torque required to assemble the fastener to the appropriate angle starts to fall off then the assembler has to realize this and correct the problem.

But, torque angle is still far far better than just torque alone. The "torque" part of the specification is designed to just take the "slack" out of the joint so that all the angle is going into stretching the bolt. The factors affecting torque go up astronomically once the bolt starts to stretch and the torque gets high so the initial torque setting is deliberately as low as possible to just take the slack out of the joint so that the torque will be as accurate as possible and then the angle achieves the critical load by stretching the bolt.

We measure bolt stretch routinely in blind holes be grinding the ends of the bolts parrallell and square and then with a sonic probe we can measure the length of the bolt by bouncing sound waves down the bolt and measuring the time between the echoes. This enables you to determine that the correlation between angle and bolt stretch to set up the specification. The thread pitch ie. if there's a thread every 1.0mm then turning the bolt will stretch it 0.50mm. It helps to roughly determine the angle required and then actually measuring the stretch sonically confirms it. The production equipment is verified regularily with the sonic testing equipment to confirm the bolt stretch is there.

A bolt is simply a spring so the bolt diameter, material and metallurgy will determine it's spring rate so that we will know exactly what kind of load is available as the bolt stretches. The bolts coming into the manufacturer for all critical joints are certified vs. a load curve specification and routinely checked so that we know that the proper clamp load is being applied for the stretch that we can then monitor.

Actually measuring the clamp load in the joint is very difficult if not impossible to do non-destructively so all the manufacturer can do is to control and monitor the factors affecting the clampload ie. the bolt spring rate and the bolt stretch.

haymaker
10-07-04, 05:22 PM
Wow! That’s what I call a complete answer. You receive an A+ using my grading system. That is a great deal of useful information. Based on the number of reads and replies to this thread many are interested in this subject. Thanks to you we all have the facts as per the assembly plant head bolt installation procedure. I hope I’m not going to the well too often but everyone knows an interesting subject always has more questions than answers.

So based on your explanation of the machine and the process. Are you of the option that it would be at or nearly impossible for one head bolt per side to only receive the 22lb/ft and not the additional 180 degrees of rotation?
Last one???? What happens during this head bolt tightening process if one or more of the bolts doesn’t fall into the machines set parameters as to pass or fail?

Thanks for giving your time and sharing the knowledge. If there is a way I will buy you lunch

Anthony Cipriano
10-07-04, 10:29 PM
You never say ANYTHING is impossible but I'd say that it's very improbable that a head bolt could leave the factory without the correct tensioning procedure.

All of the machine's spindles are interlocked to the assembly line so that if any one of them fails the tensioning procedure it'll automatically sideline the engine. For that engine to return to the assembly line it has to go back through the multiple where all the head bolts are loosened and retensioned so as to pull them all down simultaneously as intended. Generally, if the engine is rejected then a repair expert determines the cause of the reject, the spindle number, etcetera and takes the appropriate action. The defective holes must be "bought off" electronically as repaired and the engine returned to the assembly line to go back through the head bolt multiple. Usually, it is something like a burr in the hex that caused the drive tool to not engage on a bolt or something like that. The head bolt would be replaced in that case.

If a hole is found to be stripped (rare but could happen) then the line is stopped, the reason for the stripped hole is determined and the entire process purged of material so affected before starting up again. I was told about an occasion for something like this was a large chip trapped in a head bolt hole that caused the head bolt to stop due to the material built up ahead of it in the hole. Blocks were inspected for chips in head bolt holes and ultimately the final block washer was found to have a broken wash nozzle for that head bolt hole. Blocks produced in that time frame were rewashed to make sure that the holes were all purged of chips. Then the process was started up again.

As the machine tensions the bolts there are a number of factors that are monitored and recorded for the engine to pass.

Each spindle has dual angle encoders which must show the correct angle and they must agree.

The computer counts the motor revolutions by "looking" or counting the armature pulses in the drive motor to verify the spindle encoders.

In addition to looking at and tracking the angle during the angle portion of the rundown the bolt torque is monitored. Even though the angle is the primary tightening parameter the torque to reach the angle MUST fall into a specified band to confirm the angle was stretching the bolt and not just stripping or bottoming.

The torque and angle and torque-to-angle data for each of the 26 spindles for every engine produced is recorded in a computer data base for statistical analysis to determine machine capability.

Absolutely NO manual repair or intervention of critical fastener tensioning is allowed in the plant. Heads, mains, rods, timing drive, damper bolt are all done on automatic equipment monitored as described above.

There's a tremendous amount of attention made to bolt tensioning as everyone involved understands the critical nature of the fasteners in the engine.

dkozloski
10-08-04, 12:19 AM
I remember reading years ago how rear ends were created for Pontiacs. The hypoid gear sets were lapped together in a bath of fine grinding compound and the exact positions and relationships of the gears were measured and recorded automatically. The housing was automatically measured and the correct shims and adjustments calculated. The shims were custom cut to size and placed in the proper location by automatic machinery. The pinion gear was installed and the housing was spread apart far enough so that the differential assembly could be dropped in and all the bolts were tightened by machinery. The number of failures of gear sets dropped dramatically as soon as human intervention was removed. This is one of the reasons that I was supprised that Cadillac appears to be having problems with rear end gear sets. For some reason engineers have to periodically go back and reinvent the wheel. It's tough to get a handle on quality control until you can control the process to the nth degree.

Anthony Cipriano
10-08-04, 06:39 PM
This is one of the reasons that I was supprised that Cadillac appears to be having problems with rear end gear sets. For some reason engineers have to periodically go back and reinvent the wheel.

What problems are you talking about with "rear end gear sets"? The independent rear suspensions and the differentials and gears they employ are a far cry from the days of "Pontiac gears".

dkozloski
10-08-04, 07:08 PM
I'm talking about the many posts on this forum describing howling rear ends. It's my experience that if a rear end is howling, the gear tooth developement is wrong, it was incorrectly setup or something changed after it hit the road like the housing became warped or distorted from stress. The point I was making was that Pontiac changed the nature of the game when they figured out how to set up the gearset automatically and get the Monday morning hangover and the Friday anticipation of the hot date out of the game. Of course, since then there have been a lot of improvements in gear tooth grinders and the like but the old timers turned out some nice looking stuff too.

Anthony Cipriano
10-08-04, 09:59 PM
I'm talking about the many posts on this forum describing howling rear ends. It's my experience that if a rear end is howling, the gear tooth developement is wrong, it was incorrectly setup or something changed after it hit the road like the housing became warped or distorted from stress. The point I was making was that Pontiac changed the nature of the game when they figured out how to set up the gearset automatically and get the Monday morning hangover and the Friday anticipation of the hot date out of the game. Of course, since then there have been a lot of improvements in gear tooth grinders and the like but the old timers turned out some nice looking stuff too.


I think most of the rear axle noise complaints that are cropping up are on the CTS-V that are very high powered cars with manual transmissions. Something about the duty cycle there may be part of the problem.

Setting up hypoid gear set pinion depth automatically is pretty common, really. In the early 70's Cadillac was building the rear axles for their rear wheel drive and front wheel drive units including machining, heat treating and lapping the gear sets and setting them up automatically.

GM builds a LOT of rear wheel drive cars/trucks with hypoid gear sets. There are very few complaints of axle noise, really, considering the number of units put on the road daily.

It certainly is possible to take a high performance car and create some level of axle noise in severe duty.

dkozloski
10-09-04, 12:39 AM
I agree that hypoid gearsets have become pretty mundane. In fact, I have a post around here somewhere that failures have become so rare that there must be a lot of new mechanics who have never seen one. All the more reason that I was surprised to hear that there have been some complaints. including some where the owners insist they have babied the cars. I wonder what the failure mode is.

sts96
10-10-04, 12:31 PM
OK back from transmission break. Pulled my cracked block from the scrap pile just had to know the full truth. cut the block at the ends of the crack the side just fell out allowing a good look at what happened. the crack shows push out fracture part way and pull apart fracture on the rest.
Sorry Anthony the break is well below the head bolt holes (time-serts) none of the bolt holes go thru to the crack so I could not have opened the crack up with just bolts in the threads all time serts are set to the same depth.looks like a bad sad case of owner stupid. I should have dye checked the block Before repairing would have saved lots of work oh the price of education. My best to you all lol sts96

haymaker
10-10-04, 06:12 PM
Great pictures. What surprises me is that you drove the car 5-6,000 miles before the crack opened and started to leak.

sts96
10-10-04, 06:52 PM
Notice the stopleak residue at the base of the cyls. That stuff really works. lol sts96

Night Wolf
10-10-04, 10:53 PM
hmm, after reading about the timesertting process....

...is it somethign that can be done without a whole work bench of shop tools?

I have been thinking about the build on my NorthStar latly... and it keeps coming down to the timesert.... I figure, once i get over this, that will be the most difficult part... I suppose a tthe least, I could bring it to the machien shop.. that will cost money though, and brining the block over there, after I just got it in my house will be a PITA....

Atleast we know the timerserts held, and weren't the problem... I would say, given the circumstanses, the NorthStar held together pretty damn good...

Insomniac
10-10-04, 11:52 PM
what is timeserting? what it needed to do the process?

sts96
10-11-04, 08:49 AM
Try www.timesert.com
sts96

Anthony Cipriano
10-11-04, 11:13 PM
Okay sts96. You win the prize we figure for the weirdest Northstar failure we have ever seen. No one has EVER seen a block cracked like that. About the only thing I can imagine is that it froze at some point. The blocks just don't break like that in any situation that I've ever seen.

haymaker
10-12-04, 12:23 AM
Sts96. How were you able to attach your pictures to your post? I have looked for the [browse] button at the bottom of my posts but to date have not found it. I have some pictures from my time-sert job that I am willing to share with the forum. Maybe I have simply overlooked the browse button but for whatever the reason I haven’t found a way to attach pictures. Any ideas?

sts96
10-12-04, 08:38 AM
Thanks for the prize makes me feel not quite so dumb...some.
Haymaker after clicking on the reply button look below the additonal options for manage attachments which will pop up a box and follow the prompts, took me only a dozen trys or so. look forward to seeing your pics. LOL
sls96

haymaker
10-12-04, 07:17 PM
At the bottom under the reply window I see “post quick reply” and “go advanced”. I clicked on “go advanced” and then I clicked on “manage attachments”. Nothing happened. No additional window. Maybe it is because I am a junior member?

sts96
10-12-04, 07:38 PM
May be a browser setting when I click on manage attachments a window opens in the upper left corner.
I click on Post reply at the left below bottom of the last message. I think I am junior member also. Scroll down to the left bottom of the page check your posting rules. lol sts96

haymaker
10-13-04, 02:34 PM
Sts96. I am running windows xp pro with all the latest updates and service packs on this machine. Maybe I will try to log on using one of the other computers around here. Which operating system are you using?

sts96
10-13-04, 03:43 PM
XP pro with service oack 2 My browser is mozilla 1.7.1 or IE 6 prefer mozilla. sts96

oldgamer
10-13-04, 04:10 PM
Just my 02. It's more depends of other things than Windows version. Check if you running some firewall software, pop-up blocking software. It depends of your IE settings too.

haymaker
10-13-04, 04:44 PM
Oldgamer.
I’m an old gamer to. I started building computers in 1990. I have most Microsoft operating from dos 3.2 on. I have computers all over the house, most networked together. Yes I do use add-blockers and a firewall but for whatever the reason windows xp pro has a problem with java script at least on my system. I have changed many settings in internet explorer at one time or another but the changes didn’t help the problem. I have changed my firewall settings but no help. The second computer to my right has windows xp home edition same network same firewall same I-E settings but it will accept java script like the windows m.e. computer on my left. The only thing I haven’t checked lately on the xp-pro machine is the cookies settings after the sp-2 install. I guess I’ll just log on using one of the other systems in the room and see if I can attach a file.

haymaker
10-13-04, 08:39 PM
I just logged in using the xp home computer. Same network same everything. I clicked on "manage attachments" the window you spoke of came right up. Go figure.. I'll find a good head gasket picture and see if I can attach it.

haymaker
10-14-04, 12:54 AM
This post is just a test to see if I need to modify the attached picture size. The picture I have attached depicts both head gaskets and bolts in their proper location as removed from my ’97 SLS. The engine had been overheating. I will be more descriptive after I have worked out the picture attachments.

growe3
10-14-04, 07:37 AM
At the bottom under the reply window I see “post quick reply” and “go advanced”. I clicked on “go advanced” and then I clicked on “manage attachments”. Nothing happened. No additional window. Maybe it is because I am a junior member?

I think you have a popup blocker workjng. The Manage Attachments" is activated as a popup.

Try turning of your popup blocker or hold the Ctrl button down when clicking ont he Manage Attachment button.

-George

Loose screw
10-14-04, 06:21 PM
Measure your new bolts lengths (and thread diameter) and compare them to the old ones. Perhaps they are too long or too fat. See if both old and new will screw in a nut the same. Also without the heads on see how far they will screw into the block If you were supplied with out of spec bolts someone may owe you an engine.

haymaker
10-15-04, 02:41 AM
N* head gasket replace documented with pictures and text. “97 SLS 77,000 miles well maintained. I kept the pneumatic impact in the drawer and disassembled my N* using hand tools. I hope those planning the time-sert installation will take the extra time needed to accurately document the repair and share the results with the forum. It would be interesting to compare the numbers. Any of my pictures that contain the word (loose) simply means, “more than finger tight but much less tight than the other head-bolts. I think some viewing these pictures may have never seen a N* head gasket or head-bolt. Maybe it will help some understand the extent and complexities of the time-sert (head gasket) repair. The numbers at the ends of the head-bolts are based on the torque sequence (Chilton’s manual). This was the only way I knew to define and refer to a particular head-bolt location in any and or all of the pictures. I still don’t understand why the gasket didn’t fail near head-bolt 1 but I couldn’t find any evidence of a failure around the fire-ring between cylinders 4 and 6. View the pictures below and come to your own conclusion.

growe3
10-15-04, 11:09 AM
Haymaker.
Nice photo layout, thanks for taking the time to share this information.
The thread rip out was exactly what I found on four head blots on one of my cars, and two Head bolts in the other car.

As we tell people Timesert ALL holes when doing head gasket repair.

Pretty much the same thing where the coolant is pulled past the fire ring into the cylinder. Doesn't look like much, but it will go through a lot of coolant, in a short time.

I had a crack in the top of cylinder 4 that was maybe part of the problem. It had been there a long time, likely since new. After some testing and consulting with Anthony, I felt it would not be a problem. I went ahead with the repairs. After a couple of years, daily driving it is still holding up fine.

Here are a couple of images of the problem area.

dkozloski
10-15-04, 11:09 AM
Anthony, it sure looks to me like someone is missing the boat here. Why the fixation on capscrews? It looks to me like a perfect application for studs and nuts. In fact some after market supplier is missing a good chance. If it were me I would look at a high strength stud with a necked section to keep the stretch out of the threads, parallel ground washers and twelve point nuts. Once the studs were installed you wouldn't have to fool with them again. It would take a little engineering to figure out the tightening procedure but that's pretty basic stuff. It's probably pure economics or incompatability with the assembly process.

Anthony Cipriano
10-15-04, 11:55 AM
Trying to assemble a production engine with studs would be a nightmare. There's a good reason that no one does it. Alignment of the studs, getting the gasket onto the studs without ripping it, getting the head onto the studs without damaging/scratching the deck surface of the heads, etcetera.

Studs don't gain anything really, except in a situation where the engine is going to be dissassembled a lot like a race engine. The same characterisitics you describe are built into the head bolts.

Capscrews work fine. The only real disadvantage is the friction in the threads when tightening. With studs you would've the advantage of the similar materials. With the head bolts this challenge is handled by the preapplied loctite coatings on the bolt threads at the factory. In addition, the performance of the cap screws is enhanced by the very thick load bearing washers under the bolt heads and the preapplied loctite material under the bolt head that's designed to act as a lubricant during tensioning and then a thread locker after assembly.

The gaskets in the photo look to have corrosion damage to the core of the head gasket based on the elongation of the coolant holes in the siamese area and also the appearance of the gasket surface.

Once coolant seeps into the cavity of the head bolts it can cause some further corrosion and damage to the head bolt threads due to galvanic corrosion. That's why the head bolts are in a separate chamber that's clean and dry and protected from the environment and coolant. If coolant seeps in there due to a failing gasket it'll do more damge as noted.

Still, the fact is that there are millions of Northstar engines on the road and a relative few of them loose head gaskets and head bolts. The cap screw design works fine, particularily once a repair with the timeserts is made. Studs and nuts and such are a major complication and a major developement program to establish the proper tensioning specs and such. Not something that you are likely to see on a high volume production engine any time soon.

Just because some aluminum threads came out with the bolt doesn't mean that the threads had failed before. Sometimes, if the joint is contaminated by seeping coolant, the aluminum female threads will simply "weld" to the bolt due to the galvanic action and come out with the bolt. The head gasket may have started to seep, then the bolts pulled the aluminum out when dissassembled. The threads would've been fine otherwise if not disturbed. The threads then need to be fixed - which is what was foreseen when the Norhtstar was designed and why the developement work with Timeserts was done and released concurrently with the engine in 1993. An approved repair procedure was designed, validated and released with the engine. It wasn't an afterthought or a reaction to head bolts failing. The failure modes of aluminum threads were analysed and it was realized early on that some threads would need repair at dissassembly for a number of reasons. So, the repair procedure was developed with timesert.

Just because an occasional thread is failed or pulled threads are noted when bolts are removed after 10 years of operation and 100k of miles is no indictment for the fastening system used. I've worked on aluminum motorcycle engines for many years myself and have gotten pretty used to timeserting and helicoiling bolt holes in aluminum. Aluminum threads wear out with repeated dissassembly and reassembly and they react to galvanic corrosion over time in the presensce of a corrosive atmosphere. And they need to be repaired. That's why there's a procedure to do it.

The joint doesn't need to be redesigned given the success in the vast majority of engines out there.

Besides, I've seen pulled threads and broken bolts in cast iron blocks. Does that mean that the cast iron threads should be inserted, too?

I've said this before and really believe it's true. Most all of these head gasket and head bolt failures are happening on older engines at a lot of miles. Not much else goes wrong with a Northstar engine, otherwise. At high miles, it's showing to be the "weak link". It's repairable in a straight forward fashion if the proper techniques are employed.

The Northstar and Cadillac are becoming their own worst enemies here. The cars are lasting so long and showing to be in such good condition with well over 100,000 miles on them that people are expecting them to go further and further and last longer and longer with absolutely no problems. It just doesn't happen. Sooner or later something succumbs to the effects of time, miles, heat, thermocycling, lack of coolant system maintenance, etcetera. At least it's repairable and the engines don't need rings, bearings, head jobs, etcetera that's the common thread in all the complaints that the ONLY thing needed is the head gasket and bolt hole timeserting.

If this many DIY'ers are doing the timesert repair successfully just think how much money a shop could make doing it on a regular basis. If they would just follow the directions and quite trying to reengineer the joint...

dkozloski
10-15-04, 01:23 PM
Anthony, all good points. I'm used to working with engines that are intended to be overhauled many times and nowdays most cars are consumables like toasters. I noticed that the engineers were forced to Siamese the cylinders to make the engine short enough to fit between the wheels. The thermal properties of the aluminum block help to transfer heat from between the cyls but it seems to me that you still would get more differential expansion between the head and the block than you would like plus some cylinder distortion. My experience is that Siamesed cylinders wear towards each other from the higher heat in that area. All design is compromises I guess.

Anthony Cipriano
10-15-04, 02:17 PM
Yes, all designs are compromises. There are good points to siameseing cylinders and bad. Tying the cylinders together at the siamese areas makes the column of the cylinders stronger which is a good thing with an open deck design block. The siamese area actually cools pretty good due to the thermal conduction of aluminum. It adds some structure to the cylinders which is good for any bowing or longitudinal distortion of the cylinders. Unfortunately, it tends to add to the circumferential distortion of the cylinder bore due to the non-uniform thickness of the cylinder walls. On the whole, I would say that siamesed cylinders are neither good nor bad. You just have to account for the design characteristics with the cylinder bore finishing machining, distortion due to clamp load and thermally induced stress and such. The rings are actually very compliant to distortion induced by the siameseing so it's not nearly as bad a thing as one might think. Like I have said many times - there's no "perfect" design for all situations. There are always pros and cons for any design in any given application.

As an example, top fuel dragster engine blocks are solid aluminum with no water jackets. To them, siamesed, non-siamesed, whatever type of water jacket you put in the block would be unacceptable for strength as the cylinder pressures of a top fuel engine would blow out the cylinder walls. They only have to run under load for a few seconds so there's no need for cooling/coolant given the thermal inertia of the aluminum block and head so any cooling provisions would be a "compromise" to them. It's an extreme case but just serves to illustrate that ALL designs are compromised from some viewpoint. Nothing works perfect for everybody.

dkozloski
10-15-04, 02:46 PM
We used to fill the blocks in top fuel engines with two-part resin. I think the product was called Block Rock.

haymaker
10-15-04, 06:14 PM
Anthony. As to the gasket being corroded? Like I said in the earlier post the car had always been maintained well and serviced by a Cadillac service department. The service department at 56,000 miles at the end of November 2000 replaced the water pump, belt and coolant. The factory coolant was in the engine for nearly four years and 56,000 miles so the coolant should still have had some life remaining. Then being changed at 56,000 to the present 77,000 miles although it had been overheating for a while so a lot of new dex-cool was making its way into the system. The change of coolant had 21,000 miles and less than four years. I do have all the service records.

When I take the gasket out in direct sunlight the area of the leak outside of the fire-rings appears to have been very hot rather than being corroded. I don’t know the temperature or velocity of the combustion gases as they pass by the fire-ring and move on to the water jacket around the cylinders. I would think the hot gases would have a negative effect on that part of the gasket.
As to the picture of the block threads on the bolt. That bolt just carried a greater number of threads out of the block than the other bolts. Some carried two threads but most bolts only the top thread. Based on other posts this is what I expected to see. A bolt loctited into aluminum under tension for more than seven years I would think at least part of that marriage would remain intact upon removal of the bolt.

To me the threads coming out of the block during the bolt removal is not remarkable.
What I consider remarkable is the number one head-bolt on this side and the number 7 head-bolt on the other bank being not being in tension. It stands more to reason in my old brain that the loose number one bolt would have more to due with the head gasket failure than corrosion.

haymaker
10-15-04, 06:20 PM
Growe3. Great pictures. The markups make all the difference.

Anthony Cipriano
10-15-04, 09:57 PM
To me the threads coming out of the block during the bolt removal is not remarkable.
What I consider remarkable is the number one head-bolt on this side and the number 7 head-bolt on the other bank being not being in tension. It stands more to reason in my old brain that the loose number one bolt would have more to due with the head gasket failure than corrosion.


I don't necessarily disagree with you. It's impossible to say why those bolts were not under tension. The gasket firering definitely shows heat degradation as you noted. That is collateral damage after the gasket started to collapse, however.

When the steel substraight of the gasket starts to fail or lose it's resiliency due to corrosion or whatever, the gasket wont retain the proper clamp load and will start to leak. Then it's all down hill.

Without actually holding the parts and doing some more examination it's really hard to predict the cause of the failure. Sorry.

Anthony Cipriano
10-15-04, 10:10 PM
. I'm used to working with engines that are intended to be overhauled many times and nowdays most cars are consumables like toasters. s.


Understand that the Northstar engine is as "rebuildable" or re-manufacturable as any engine. It does take some special tools and processes to do it correctly but what engine doesn't? Just because the techniques are different from other engines doesn't make them wrong or throwaway.

If there was a serious demand for remanufactured Northstar engines I can assure you that companies would be all over it.

I've worked with several companies who remanufactured the 4.1, 4.5 and 4.9 engines. We were "told" the same thing about those engines. That they were throwaway and not capable of being remanufactured. After showing one company (EngineMaster) how to do it and reviewing the correct procedures they demonstated durability on dyno tests with their remanufactured engines that was equivalent to brand new factory engines. After the remanufacture program was underway and the supply of core engines and parts was flowing, Enginemaster found that they could re-manufacture the 4.x engines for less cost than any other engine that they'd done (and they've been doing this for 50 years or more), that the percentage of reclaimed parts from the core engines was higher than any other engine that they'd ever done and that the quality of the remanufactured engines were better than any engine that they'd done. So much for being a throwaway. Right?

The same holds true for the Northstar. The cylinders can be overbored by design as much as 1 mm. The rest of the parts are just as serviceable and remanufacturable. Someone just has to take the time to do it. There's very little demand for remanufactued engines and such for two reasons. The quantity and quality of used Northstar engines available in scrap yards is plentiful which negates demand for "remans". Also, GM is still servicing with brand new engines for all model years of Northstar. As long as new engines are available the demand for "remans" remains low.

If there's ever a demand for remanufactured engines then the process can be started up relatively easily. Currently it's less expensive and easier to simply service with newly assembled past model engines since the parts are still manufacturable.

"Re-manufactured" or "rebuilt" aircraft engines are a bit of a misnomer. Most of the parts are replaced. The entire cylinder, jug, head assembly is generally replaced due to heat checking and cracks since the cylinders are air cooled and suffer some severe thermal gradients. About the only thing used over again is the crank and block. Besides, for what a reconditioned Continental or Lycoming costs one could buy 4 or 5 Northstar engines.

haymaker
10-17-04, 01:47 AM
I started this thread 9-21-04. I would like to take a moment to thank everyone that has replied. Based on the number of views this subject is interesting. The original question (post) being
Has anyone successfully replaced the head gasket on a Northstar without timeserting the block? I mean hands on replacement not a secondhand story.

As of tonight no one has come forward stating that they have successfully replaced the head gasket(s) with out first time-serting the block. A few days ago the dealer’s service department replaced my fuel rail [recall]. While in the service department I asked about the head gasket repair. I was sent to the service manager’s office. I asked the service manager “have you replaced the head gasket on a N* with out first time-serting the block”. He stated in the earlier years his mechanics replaced the head gaskets with out time-serting. If the bolts could be reinstalled the head gasket repair could be completed. He also stated that today, the time-sert installation is the only accepted method for them to repair (replace) the head gaskets. Looks like I found my own answer. Just thought I would share the information.

Anthony Cipriano
10-17-04, 02:04 PM
Regarding the strength of the aluminum head bolt threads in the block and so forth, I've seen multiple head changes on a Northstar block during development without timeserting. So, the threads are certainly capable of being reused as is. Obviously, these are relatively new parts that, in many cases, did not stay together for very long before they were dissassembled and reassembled.

In addition, in the early days of the Northstar engine, there were no engine repairs allowed in the field. Every engine complaint was an engine R&R so that the engine could come back to product engineering for analysis. During that time there was the opportunity to tear down multiple engines for a variety of complaints. Once the problem was ascertained the engines were reassembled for dyno confirmation of the correction. There was never an issue with reinstalling heads multiple times on the same block without thread problems.

I suspect that what's going on today is that engines in the field have many years of time on them. Something that's difficult to speed up in the lab and on accelerated endurance testing. It appears that once the bolts are in the block for many years it's much more common for threads to come out when the head bolts are removed and to run into problems with head bolts upon re-assembly.

Based on my experience with lab engines I'd say that the head bolt threads in the aluminum block are very robust and good for many applications of the head bolt tensioning. I've changed my personal opinion on field engines with a lot of miles and many years on them, however. I feel it's certainly a prudent thing to do to install the thread inserts on any engine that's torn down for whatever reason due to the high likelyhood of head bolt thread damage upon dissassembly, damage during cleaning of the threads and damage during reinstallation.

I don't know that this condemns the original design as there's still the fact that the vast majority of the Northstar engines run fine for many years and hundreds of thousands of miles with no head bolt (or head gasket) problems. The ones that do have an issue in this area for whatever reason seem to need the timeserting to positively guarantee a solid repair.

The unknown here is what would've been the circumstances if the timeserts had been installed from day one. Possibly the same thing would happen with father time involved and then the head bolts would lock to the inserts and pull them when the head bolts were removed thus making a repair even more difficult if not impossible. Just a thought. The nice thing with the situation as is is that there's a known, proven, readily availble and easily doable repair procedure that guarantees results. The need for repair of head bolt threads was recognized from the very beginning which is why it was developed and validated with the timeserts. The mistake might be that it was assumed to be a selectively necessary repair in case of a head bolt breakage, overtorque, crossthreading, etcetera instead of something that's mandatory at high miles and many years.

All the remanufactures on the 4.1, 4.5 and 4.9 engines are done with timeserts in all the head bolt holes in the aluminum block. The program originally started without doing this and was very successful in the validation stages but once the volume of remanufactured engines started through the program there was a low but steady fallout of head bolt holes at head installation. This would then slow the process down to sideline the engine and repair with a timesert. Quickly it became more economical to just machine the block for timeserts when it was being touched up in maching anyway for the remanufacture process and avoid any head bolt fallout later on in the process. I'd assume the same logic would apply to the Northstar in an eventual remanufacture situation and thus would apply to field service of older engines.

haymaker
10-18-04, 09:30 PM
I became so engrossed with the head gasket on the other side of the engine the one with the leak between cylinders 2 and 4 that I nearly forgot to closely inspect the other one. Today I performed a much closer inspection on the head gasket from the other side of the engine. Am I ever glad I installed the time-serts on both sides? This side was leaking worse that the other side or at least that is the way it appears. The area of the leak across the fire ring appears larger than the one on the other side. The leak is from cylinder 1 into the water jacket. It is between the top of the gasket and the cylinder head. The bottom side of the gasket in this area looks fine. All the head bolts but one on this side of the engine was in tension. The one head bolt that was much less tight than the others was at the other end of the engine at the top left of cylinder 7 it also had standing oil in the bolt cavity. The head bolt at the top right of cylinder 1 was oily but still under tension. No wonder the coolant came out so fast. Both head gaskets were leaking.

I think the leak between cylinders 2 and 4 was allowing me to drive for a day or two with out adding coolant but the leak from cylinder 1 was the one keeping me off the freeway because the last few times I used the freeway the car would overheat in a very few minutes.

I would suggest that Time Fastener Company include all twenty inserts in the kit rather than only the ten supplied. That may encourage everyone to install them all.

If any of you are planning to time-sert just one side? This could be your Northstar. lol

Night Wolf
10-18-04, 11:45 PM
Anthony... what you siad makes me think about something...

While my N* is about 10 years old... from looking at the enigne and valvetrain, there is hardly any wear on any parts... the engine was donated by GM to a tech school... it was built, ran a few hours tops, then torn down...

... I looked with a light... all the threads are in the holes... none seem to be damaged....

...under the circumstances with my engine, does the timesertting *reallY* need to be done? is there any way to see how much use the engine has? I just can't imagine the origanal threads being stressted that mcuh... the enigne was never under a load either... (AFAIK)

Anthony Cipriano
10-19-04, 04:08 PM
I'd think that an engine that's never been run would have like new threads for the head bolts. If there's never been any thermal cycling of the engine to really load the head bolts they are likely okay. On the other hand, aluminum threads will wear with repeated tensioning. Given that it was a school engine and possibly assembled/dissassembled many times - and who knows at what torque settings, etcetera - the threads could have been damaged like that.

Given the work you are going to do and what you'll learn about it I'd recommend timeserting as the engine is a complete unknown. By the way, lots of engines donated to schools by GM are SCRAP engines with known manufacturing defects. If an engine fails an end of line test or has some other known defect then it's sidelined to be torn down. Many times these scrappers are donated to schools for auto shop classes with the understanding that they are scrap and not running and have potential problems. There's no real way of knowing except for carefull observation during assembly.

dkozloski
10-19-04, 05:56 PM
In 1941 Allison GM engines and parts for Curtis P-40's were in short supply. Claire Chennault arranged for spare engines to be made up for the American Volunteer Group (Flying Tigers) P-40's out of "scrap" and "rejected" parts. I talked to an oldtimer that worked for Allison at that time and he said that the extra care that went into using the marginal parts more than compensated for any defects and the engines wound up with an enviable service history. A large percentage of the defects were comsmetic and didn't affect the servicability of the parts.

Night Wolf
10-19-04, 10:15 PM
this enigne that I have seems to be mint... I had a family friend that owns a machien shop quickly look at it, he siad it is in nice shape too...

... any specific areas I could take a pic of and maybe show you to help determin how mush use is on the enigne?

haymaker
10-26-04, 01:15 AM
Night Wolf. You going to timesert or not?

chevyorange
10-26-04, 11:18 AM
<snip>

Still, the fact is that there are millions of Northstar engines on the road and a relative few of them lose head gaskets and head bolts. The cap screw design works fine, particularily once a repair with the timeserts is made. Studs and nuts and such are a major complication and a major developement program to establish the proper tensioning specifications and such. Not something that you're likely to see on a high volume production engine any time soon.<snip>

Okay - newbie here, haven't even bought a N* powered car yet, but am I to take this as something I should do no matter when when I buy the car? (Replace the head bolts)? Or is this only after a certain failure.

I have to admit, I am scared to death of the N* after reading some of this! I know that the odds are that the car is fine (Pacific Northwest car, very little freezing and only a couple days with high temps in the summer and 87k miles).

I love everything about the car and am willing to expend a certain amount of money to own one, I think the 6K asking price leaves me with a few grand in my pocket to jump on repairs/maintenance that might need to be done - but like you mentioned, there are millions of N* engines on the road and if they were bad, there would be a ton of web pages with the haters spewing their stuff.

Thanks to everyone in this thread for their frankness in answering questions and pointing out weak spots in this magnificent engine.

Adam
(chevyorange)
http://homepage.mac.com/chevyorange (yeah, I'm a Chevy man making my first move up to the top of the GM chain!)

sts96
10-26-04, 01:38 PM
I have been as deep as possible in two N* engines and 1 transaxle this year they have the best fit and finish of any out there. Some problems will happen to any car most are caused
by driver, owners, users.I think some people can tear up a anvil with a rubber hammer. Cadillac and Northstar as long as I drive, ride. You will not find more car for the money. sts96