: 1994 STS Headbolts



Corbett Price
10-01-04, 07:47 PM
I recently purchased a 1994 STS with the Northstar engine. I got a great deal on it with the notice it needed to have one or more helicoils put in for loose headbolts causing overheating. The local mechanic is trusted and experienced, but I stumbled my way here and want to ask anyone with experience about it. I've read some about it here, but need more information. Apparently this is a design flaw among at least the first Northstar engines. Is there any recourse through Cadillac for at least partial compensation for repairing a flawed engine they sold?

The mechanic told me that several years ago he installed a couple helicoils for the previous owner and he believes I am having the same problem. He says he could do the same thing for whichever bolts are loose now, but it could happen with other bolts in the future. He recommends replacing the engine. I can get a rebuild for about 4800 bucks. I'll probably do that unless I can come up with some other suitable solution. Any help?

You can either reply here (probably best for anyone else with the same problem,) or email me directly at Corbett@direcway.com
Thanks

Corbett

sts96
10-01-04, 09:33 PM
I think time serts are better than helicoils but did not work out for me, found a used engine with 80k miles it passed compression check and leak test now have 600 miles with no problems I think a used engine with a warranty is a better buy. lol sts96

Ranger
10-02-04, 11:51 AM
Apparently from what I have learned this is a problem with any aluminum engine. As mentioned, DO NOT use helicoils. They will fail. Use "Timeserts" designed for the Northstar and timsert every head bolt hole, need it or not so you don't have to come back and do it again later (and you will if you don't do them all).

dkozloski
10-02-04, 06:03 PM
A properly engineered Heli-Coil installation will work just fine but you won't find the specialized inserts and tools you need at an auto parts store. Contact Emhart Teknologies directly to make sure you get the right stuff. You will also find it is much cheaper than TimeSerts.

BeelzeBob
10-02-04, 10:25 PM
A properly engineered Heli-Coil installation will work just fine but you won't find the specialized inserts and tools you need at an auto parts store. Contact Emhart Teknologies directly to make sure you get the right stuff. You will also find it is much cheaper than TimeSerts.


Absolutely, postively WRONG.

Timeserts have proven to be much stronger and much more resistant to pulling the inserts out of the virgin material of the block than helicoils. Helicoils are an excellent product but they are NOT the correct repair for head bolts in an aluminum blocks. Helicoils are like a slinky in that they are a coil that is installed into the virgin material and each thread carries it's own load in the parent material. The timeserts are a solid insert so that the load from the ID threads are spread out over the entire OD threads which makes them much stronger. In additiona, there are NO helicoils long enough to properly repair the Northstar head bolts as they are not long enough to provide the proper thread engagement on the OD thread. The Timeserts for the NOrthstar block are application specific parts that were developed for the Northstar block specifically with Time so as provide the correct thread engagement on the ID and OD threads.

Timeserts are the ONLY approved means of repairing a head bolt in the Northstar engine. Period. Helicoils have been PROVEN to not hack it. Period.

BeelzeBob
10-02-04, 10:32 PM
I recently purchased a 1994 STS with the Northstar engine. I got a great deal on it with the notice it needed to have one or more helicoils put in for loose headbolts causing overheating. The local mechanic is trusted and experienced, but I stumbled my way here and want to ask anyone with experience about it. I've read some about it here, but need more information. Apparently this is a design flaw among at least the first Northstar engines. Is there any recourse through Cadillac for at least partial compensation for repairing a flawed engine they sold?

The mechanic told me that several years ago he installed a couple helicoils for the previous owner and he believes I am having the same problem. He says he could do the same thing for whichever bolts are loose now, but it could happen with other bolts in the future. He recommends replacing the engine. I can get a rebuild for about 4800 bucks. I'll probably do that unless I can come up with some other suitable solution. Any help?

You can either reply here (probably best for anyone else with the same problem,) or email me directly at Corbett@direcway.com
Thanks

Corbett


You buy an 11 year old car with a known head gasket problem and are enquiring about whether there is any recourse with the manufacturer....LOL LOL LOL sorry.....

Take the money you saved and have the head gaskets replaced. Timesert the head bolt holes for extra insurance but that is not likely the root cause of the problem with an engine with that many miles/years on it. Timeserting the block is a routine procedure with excellent results if the correct materials and procedures are used. There is a specific timesert kit for the Northstar headbolt holes that is marketed by Time engineering or thru the GM service tools.

Most of the head gasket problems on the early (93/94/95) Northstars come from lack of cooling system maintenance. The 94 was factory filled with the conventional green silicated coolant that needed to be replaced every 2-3 years/24-32K miles. If this was not done then the corrosion inhibitors in the coolant would fail and internal corrosion in the engine lead to failure of the head gaskets as the head gasket core will simply rot out from the inside out at the coolant passages. When the head gaskets are serviced the head bolt holes can often be damaged and of course the head bolt holes are blamed. If the proper procedures are used the head bolt holes are generally very reliable but the timeserting will guarantee success.

dkozloski
10-02-04, 11:09 PM
bbobynski,my experience is with aerospace applications with bolts used to assemble guided missiles that are far more intense than any automobile engine. One example is 1/2 in diameter bolts threaded into magnesium castings for a distance of about 2 1/2 inches using Inconel Heli-Coil inserts and then torqued to over 240 foot pounds. I suspect that you are right about Timeserts and the average garage mechanic though.

BeelzeBob
10-02-04, 11:18 PM
bbobynski,my experience is with aerospace applications with bolts used to assemble guided missiles that are far more intense than any automobile engine. One example is 1/2 in diameter bolts threaded into magnesium castings for a distance of about 2 1/2 inches using Inconel Heli-Coil inserts and then torqued to over 240 foot pounds. I suspect that you are right about Timeserts and the average garage mechanic though.


Yep...big big difference....LOL LOL

No doubt it is possible to obtain a particular helicoil insert that might work in the Northstar head bolt area...but...the helicoils that are commonly available "on the street" will definitely NOT work. You would really have to look deep and do some development to find a helicoil that would work and it would have to be a solid insert style not the conventional slinky design you see on the street. We are talking about simply buying inserts and installing them in a garage here...not "engineering" or "re-engineering" the joint.

I bet EACH of the helicoils you describe probably cost more than a brand new Northstar engine....LOL LOL LOL

Most of the aerospace fasteners like you describe that I am familiar with use a tapered thread that gradually changes pitch a tiny bit so as to evenly load the bolt along the length of the threads as it is stretched. Are the inserts designed to accomodate this as the tapped holes for that style of bolt are special taps that are designed to go to a specific depth to cut the correct thread pitch to match the bolt.

dkozloski
10-02-04, 11:37 PM
bbobynski, your correct about the pitch of the thread being fudged to obtain even loading. In fact the bolt is pretty tight even before it starts to take up the tension. What is the mechanism that is causing the fastener failures in Northstars? I managed an aircraft engine overhaul shop for over ten years and that was all aluminum castings Heli-Coils and high strength fasteners. A stud or bolt that wouldn't take the torque was a rare event unless there was obvious abuse. With all the trouble with Northstars maybe some engineer needs to get called on the carpet and explain why the system doesn't last. Fastener choice and design is pretty basic stuff.

BeelzeBob
10-02-04, 11:52 PM
I think that a lot of the supposed fastener failures are not fastener failures but head gasket failures and then botched repairs causing a head bolt to later strip or fail. Granted, there have been some cases where a head bolt hole has failed but they don't account for the majority of the head gasket cases. The head gaskets can start to fail on the all aluminum engine at higher miles if the coolant system is not maintained, etc... If the mechanic at the repair doesn't clean the head bolt holes correctly, use new head bolts, cleans the head bolt holes with a cutting tap, oils or lubes the threads of the head bolts, etc... it can easily cause the head bolt threads to fail.

Head bolt hole problems can be traced to a bit of porosity in the casting in the thread area which might weaken the threads, corrosion due to using the wrong coolant mix in the coolant system (using over 50% DexCool is very acidic and the fumes can enter the head bolt cavity and cause head bolt problems) possibly a bad bolt with a nick in the threads that can weaken the female aluminum threads, etc. Almost an infinite number of potentials.

I think the difference in your aircraft experience and the Northstar engine is volume. We make as many Northstar engines in one day as most aircraft engine manufacturers make in a year..... Typically, most aircraft fasteners are a different grade and holes are inserted as a matter of course whether they need it or not.

Aircraft engines are no panacea for durability....!!! Most are aircooled and do not have head gaskets so as to avoid the problem of the head gasket joint in passenger car engines....i.e..the cylinder jugs are one piece cylinder/heads with no head gaskets or head bolts to deal with. They avoid the highest stressed joint in a liquid cooled passenger car engine. Besides, from all the air worthyness directives that I have seen on broken cranks, cracked cylinders, etc....the standard light aircraft piston engine has a very high failure rate based on the limited number of them out there. With several million Northstar engines on the road there are some failures...you read about them on this forum for sure...but the thousands and thousands of them running around fine for hundreds of thousands of miles are rarely heard from so some of the head bolt joints do work fine.

Night Wolf
10-03-04, 12:00 AM
How much does the complete time-sert kit cost? (for the tools and everything)

growe3
10-03-04, 12:49 AM
How much does the complete time-sert kit cost? (for the tools and everything)

My set which I purchased directly from Timesert.com was $294 + ten extra inserts @$2.58 ea, for a total of $319.80.

Always do all of the bolts. If yours was Helicoiled and they are failing, you may need to have the large size Timesert kit.

-George

Timesert Link
http://www.timesert.com/misc.html

Timesert FAQs
http://www.timesert.com/FAQ.html

Night Wolf
10-03-04, 01:20 AM
what was the reason you bought 10 extra inserts? you need them, or just to have extra?

I am going to have to do the time-sert when I go to put the heads on my N*.... ugh... $320... almost twice what I paid for the enigne... but it has to be done... that will be a couple weeks of saving up and not spenidng much this winter....

Is it a difficult process? I was reading thru the directions... I have a cordless drill, is it somethign I could do myself? I know that the time-sert needs to be done.... but I don't know *how* it is done...

Rob Benham
10-03-04, 03:20 AM
Hi,

My 94 SLS seemed to need a specific coolant, could anyone confirm the type as it seems quite critical. I have had conflicting advice (and written data) in the past.

My days of Toyota Supra head gasgate replacements seemed a lesson in always having the head skimmed. RB

Night Wolf
10-03-04, 07:26 AM
in '94 it uses regular green coolant... but you need the GM supplment tabblets... get them at the dealer...

growe3
10-03-04, 11:49 AM
what was the reason you bought 10 extra inserts? you need them, or just to have extra?

I am going to have to do the time-sert when I go to put the heads on my N*.... ugh... $320... almost twice what I paid for the enigne... but it has to be done... that will be a couple weeks of saving up and not spenidng much this winter....

Is it a difficult process? I was reading thru the directions... I have a cordless drill, is it somethign I could do myself? I know that the time-sert needs to be done.... but I don't know *how* it is done...

The Timesert kit comes with 10 inserts, to do all of the head bolt holes you need to get an additional 10. This is so you can do all 20 head bolt holes.

You will more than likely pull out threads when the bolts are removed. Other holes will have been weakened. If you try to skimp and not do all 20 holes, you will probably strip a few when tightening them up. Skimping here is a big mistake.

The Timesert part of the head gasket repair alone usually cost about $450 -$500 at a dealer.

It is not particularly difficult for anyone with a good background working with power tools, and will follow the directions with care.

I would not try using a cordless drill. This process will take about 5 hours or more.

You will need a 1/2" drill motor, compressed air to blow out the holes as you work and after. Spray brake cleaner to flush all of the oil out of the holes after they have been drilled and tapped. The holes most be clean and dry before screwing in the Timsert with the thread locking glue on it.

A good set of normal mechanics hand tools will get the job done, along with patience and a helper.

Caution:
Removing and replacing the heads on a Northstar is not for the partially informed. You most have the proper tools or you will likely damage many parts. The most important tool is.....a set of factory service manuals!! Then read and understand the procedures, before just unbolting the easy to get at bolts. Failure to do so is setting yourself up for a failed repair job.

I have fixed and rebuilt many engines. After gaining experience in them, the only thing I needed from the manual were the bolt torque specs. The Northstar is different in that special tightening and assembly methods most be followed correctly for success. A number of these methods changed between engine generations and are not obvious to the casual observer.

There are a number of special tightening methods that must be followed to prevent damage to critical parts. There are some not so obvious differences from year to year. If you do not follow the methods for you car, you will likely break or damage something.

-George

growe3
10-03-04, 11:54 AM
Hi,

My 94 SLS seemed to need a specific coolant, could anyone confirm the type as it seems quite critical. I have had conflicting advice (and written data) in the past.

My days of Toyota Supra head gasgate replacements seemed a lesson in always having the head skimmed. RB

As Night Wolf said; use the green coolant only.

The supplement is Bars Leak Gold Seal, readily available at many stores. Use two tubes (or 6 pellets) placed in the radiator hose at the water pump. Do not place it in the surge tank!! It will not circulate from there.

-George

Ranger
10-03-04, 12:45 PM
Hey Night Wolf, timesert kit for sale.
http://caddyinfo.ipbhost.com/index.php?showtopic=3539

Night Wolf
10-03-04, 02:58 PM
The heads are already off of my engine.... I bought it that way.

hmmm, it dosn't seem like I have all the correct tools needed... I will have to see...

chevyorange
10-25-04, 10:56 PM
in '94 it uses regular green coolant... but you need the GM supplment tabblets... get them at the dealer...

So, if I buy the '94 STS I'm looking at tomorrow, when I do/add/change the coolant, I have to get some supplement tablets? I can't use DEX-COOL when flushing the WHOLE system?

Thanks,

Adam

growe3
10-25-04, 11:14 PM
So, if I buy the '94 STS I'm looking at tomorrow, when I do/add/change the coolant, I have to get some supplement tablets? I can't use DEX-COOL when flushing the WHOLE system?

Thanks,

Adam

Change the coolant soon, so you know it is fresh.

The supplement is Bars Leak Gold Seal, use two tubes, or 6 tablets, added to yhe upper radiator hose, not the surge tank; the supplement is available at many stores.

Stay with the green coolant. The engine was designed to work with it. The green coolant helps prevent corrosion by depositing silicates. Using the orange coolant won't hurt, but you also will not get the longer life from it. It uses a different method of corrosion protection and the silicates already in your engine will prevent the orange coolant from providing a longer change interval.

Replace using a 50/50 mix.

-George

chevyorange
10-26-04, 10:23 AM
George, thanks for the info. Now I just have to drive to look at the car this AM. My brother is driving me up just in case I like the car!