: Northstar stud problem



'90 Eldo
07-18-05, 03:37 PM
I just learned of a car for sale that has a Northstar engine with a problem where the studs are pulling out of the block,apparently someone overtorqued them? Can this be fixed? If so can it be dependable?

dkozloski
07-18-05, 04:36 PM
There must be a thousand posts on this subject by now. Do a search on headbolts, head gaskets, Time-Serts, and blown gaskets. By the way, it is bolts and not studs that have thread problems.

'90 Eldo
07-18-05, 05:29 PM
Thanks for the input. I just heard the guy say it had studs I don't know much about the engine. I will look up the info you mentioned on it . I'm a newbie so I appreciate your patience here.

zonie77
07-19-05, 12:59 AM
Look in the tech section for the head gasket post. There is a link to an illustrated article on installing timeserts.

dkozloski
07-19-05, 01:43 AM
'90Eldo, to answer you question in a nutshell, some Northstar engines have problems with pulled threads and blown head gaskets. They can be fixed good as new by a reasonably handy mechanic that can follow directions. Some of the tooling required is an added expense.

peteski
07-19-05, 01:59 AM
90 Eldo - if your car is same as your name: 1990 Eldo, then it doesn't have a Northstar engine. So, you wouldn't have the "stud problem"

'90 Eldo
07-19-05, 11:52 AM
The car I'm referring to is a newer Sedan DeVille that is about to be towed. The car is nice other than the engine problem. I thought it would be worth fixing and reselling if it can be dependable. Is the problem symptomatic of the engine itself or is this something mechanics are doing to the engine when they are r&r ing the heads? At any rate I appreciate your input and I will look into it further with a mechanic,thanks again.

nota
07-20-05, 11:41 PM
has any one found a source of studs to replace N* head bolts?? in proper grade ect
yes I know about time-certs still I like the idea of never ever removing the studs
from the problemmatic alloy block, just undo the top of stud nuts
IF any of my extra N* blocks are lucky enuff to unbolt without pulling out threads
btw main cap studs would be a good idea tooo

dkozloski
07-21-05, 12:19 AM
It's much trickier than it seems. Do some searches on this subject on this forum and you become Bbob educated like the rest of us. Basically; the heads, the head gasket, the crankcase, and the torque to yield bolts are all together a highly engineered and tested system that is not to be modified by the unwashed masses without serious risk of disaster.

STS 310
07-21-05, 08:34 PM
It's much trickier than it seems. Do some searches on this subject on this forum and you become Bbob educated like the rest of us. Basically; the heads, the head gasket, the crankcase, and the torque to yield bolts are all together a highly engineered and tested system that is not to be modified by the unwashed masses without serious risk of disaster.

Well said dkoz....

'90 Eldo
07-22-05, 12:29 PM
Experimenting with a replacement stud sounds tempting. I have had some experience in aluminum engines where the studs themselves will "stretch" I suppose more likely under higher compression ratios. This is a problem in Porsche engines which are being fixed using Dilivar (whatever that is) studs as a replacement. But as you stated there is the head gasket,and probably clearance problems to contend with,and this is a very expensive engine to be playing with.

Thanks for your input.

odarodle
03-20-06, 07:15 PM
You can re tap using a boot or Check with a machine shop, They have the equipment to do the job right.......

denscor
03-20-06, 11:08 PM
has any one found a source of studs to replace N* head bolts?? in proper grade ect
yes I know about time-certs still I like the idea of never ever removing the studs
from the problemmatic alloy block, just undo the top of stud nuts
IF any of my extra N* blocks are lucky enuff to unbolt without pulling out threads
btw main cap studs would be a good idea tooo


I called ARP today and inquired if they carried Head Studs for the N* to my surprise the rep I spoke to new exactly what I was looking for.
He said they have a Kit but it's not labeled for the northstar but for a VW 16 valve DOHC and the part number is: 204-4204 and you will need to of these kits.
He also mentioned that he has been selling these kits to Cadillac dealers for several years. Hmmmm interesting.
The kit has 10 studs, molylube & 10 twelve point nuts. I looked into the specs of these units and they have the M11 x 1.5mm thread and are 6.5" long (165mm) for the block side.(Stock bolts for mine are listed at 152mm) Didn't get the specs for the nut side thread, Sorry.
These babies are rated for 190,000 PSI tensile strength. WOW! ARP
mentioned Timeserts were a necessity.


Hope this helps!!!!!!!!!!!!!!

davesdeville
03-21-06, 06:30 AM
^^Hmm I read that on a Fiero forum awhile ago. Nice to know that ARP itself says the same thing.

parts68
03-21-06, 08:33 PM
thats funny when I said the same thing about head studs on another post I got flamed.
How are they torqued?by measuring stretch? torque to yeild?

Zorb750
03-21-06, 10:42 PM
Torque to a spec then torque in number of degrees turned, in specific steps and in a specific order.

chevelle
03-21-06, 11:01 PM
Torque to a spec then torque in number of degrees turned, in specific steps and in a specific order.

That works for the production head bolts but if the studs are a different metallurgy then the production tightening specs will be wrong. The production head bolts stretch considerably and are designed to stretch under load and with thermal changes in the engine. If the bolts are replaced with studs (that are presumably stiffer and stretch less for the same load) then the joint will be overloaded if the production tensioning specs are used. Guaranteed. That will cause the head gasket to fail quicker than anything.

If the problem is the aluminum threads in the block failing what good would studs do?

Read the info from ARP again. They recommend timeserting the holes in the block if studs are used. Duh. Once the holes in the block are timeserted the problem disappears. The production head bolts do not fail. Why replace them with studs...???

Using studs is addressing the wrong thing if a thread repair in the block is required.

davesdeville
03-22-06, 04:04 AM
Would the factory head bolts fail under heavier stress from, say, forced induction? Would studs not be a solution if that is the case?

denscor
03-22-06, 06:01 AM
When you use studs it puts the pressure on the nut and stud as opposed to a bolt which stresses the threads of it.


Yes forced air will lift heads, so head studs are needed. I run 11 psi on my vette and at first I used factory bolts and it lifted and stretched the bolts,changed to stud and have not lifted the heads.

JaxxMan
03-24-06, 04:58 PM
Hey denscor
Copying my post almost word for word I see, at least give me the credit. LOL!

original post:
http://www.cadillacforums.com/forums/cadillac-tech-tips/62473-arp-head-stud-option.html

My engine is going back together weekend,(part time project) will let you know how it works out if you want.

denscor
03-24-06, 07:40 PM
Hey denscor
Copying my post almost word for word I see, at least give me the credit. LOL!

original post:
http://www.cadillacforums.com/forums/cadillac-tech-tips/62473-arp-head-stud-option.html

My engine is going back together weekend,(part time project) will let you know how it works out if you want.


Sorry about that!! LOL It was a good post I even bought some for my head gasket replacement!

96-deville-man
03-24-06, 07:40 PM
Hey denscor
Copying my post almost word for word I see, at least give me the credit. LOL!

original post:
http://www.cadillacforums.com/forums/cadillac-tech-tips/62473-arp-head-stud-option.html

My engine is going back together weekend,(part time project) will let you know how it works out if you want.

wow thats pretty bad you caught him red handed and theres nothing he can do but say sorry. lol

on a more serious note. are these studs goning to hold up to say 10-12psi of boost? that is with some motor work!

JaxxMan
03-25-06, 12:03 AM
ARP themselves should know everything about your application.

If you don't have luck with them contact this company http://www.chrfab.com/ Just be aware they tend to prefer to give out advice if you buying stuff from them.

I got put in my place for asking too many questions last time I called. I only purchased some performance MLS headgaskets so I guess it did warrant the amout of questions I had. (There was a lot of e-mails also)

I don't blame him he's protecting his interests.

Good luck with your project!

P.S. just noticed on their site: http://www.chrfab.com/Engines.htm 20lbs of boost 800 HP

chevelle
03-25-06, 12:28 AM
When you use studs it puts the pressure on the nut and stud as opposed to a bolt which stresses the threads of it.


Yes forced air will lift heads, so head studs are needed. I run 11 psi on my vette and at first I used factory bolts and it lifted and stretched the bolts,changed to stud and have not lifted the heads.


Have you ever heard of the saying "for each force there is an equal and opposite force..." ???

It is rediculous to think a stud doesn't put the same load into the threads in the block as the conventional head bolts do. Yes, the "force" is on the stud and nut. And the SAME force is then trying to pull the stud out of the block just as with the head bolts.

Studs are advantageous for two reasons. If you are going to be tearing the engine down a lot (like a race engine) then the wear on the threads inside the block from repeatedly torquing the head bolts can become and issue. Particularily with an aluminum block. So studs are often used on race engines since with the stud the wear from repeated assembly goes into the nut and upper thread on the stud and the stud and nuts can be easily replaced when worn.

When stronger/stiffer'different length headbolts are needed it is easier to fabricate studs of an unusual length. Studs can be easily machined from bar stock to whatever length is required. Lots of shops can makes studs. Making a new bolt is very expensive and time consuming. The tooling for forming the bolt is very expensive in itself.

Functionally a head bolt can be made just a strong as any given stud. It is just the size of the bolt and the metallurgy. There is nothing inherently stonger about a stud and nut compared to a bolt if both are of the same material and metalurgy. Manufacturers building thousands of engines always use bolts as they assembly is much easier and the cost of the tooling for the special bolts is inexpensive when you amortize it over hundreds of thousands of engines.

If an engine was failing head gaskets under boost, for example, and was "fixed" with studs then the fix was due to the superior metallurgy and stiffness of the chosen studs, not because of the stud itself.

Zorb750
03-25-06, 05:16 AM
The only stress the stud would save would be the stress of the twisting under pressure. Once the stud or bolt is tightened, there would be no difference in stress, other than the fact that with a stud there would now be two places for the threads to fail.

I was under the impression that the general consensus regarding studs was negative anyway.

denscor
03-25-06, 05:52 AM
A good set of stud work great. I have built many race motors from mild to wild and always used studs believe me, it stresses the thread in the block if you use bolts.With this being a problem with the northstar I don't see any reason why it could not benefit from it! Another reason the newer bolt are a problem is because they are torque to yield which makes them confusing to put in and they stretch and you have to use a special wrench for proper repair!

Zorb750
03-25-06, 11:12 PM
No special wrench.

Tighten to a specific value with any old torque wrench, then in a specific order in a specific number of degrees. You could use a breaker bar for the degree part if you wanted to.

You stress threads whenever you put force on them. Studs put just as much force on threads once they are tightened as bolts do.

dkozloski
03-25-06, 11:39 PM
Because neither the stud nor the bolt draws the head on to the block over distance like the threads of a gear puller might, there is no difference in the dynamics of the two types of fasteners. Once again we find ourselves stomping on pissants while elephants are running up and down the halls. If the head to crankcase joint fasteners are the problem, the solution is to redesign the engine so it is assembled with through bolts with nuts on each end like some older engines with barrel crankcases. All the rest of the discussion is pontification on bolts vs. studs.

JaxxMan
03-26-06, 07:48 PM
Other than easier repeated reassmebly when using studs there are some additional things to consider.

I was unable to find any strength rating for the head bolts. Anyone else have luck finding a strength rating ?

Studs are reusable vs. bolts but are not recommended to reuse because they can stretch out of spec. I read posts here where bolts stretched causing the dreaded gasket failure, so if I can avoid it I will try.

In my oringinal post, I stated they are rated for 190,000 PSI tensile when I went to the ARP website today I found them speced at 200,000 PSI. Page 72-73 of http://www.arp-bolts.com/Catalog/Catalog.Images/2005ARPCatalog.pdf part #204-4204. ARP studs have a lot of engineering behind them and are contructed differently than most products and claim be 10 times stronger than other products.

My opinion is, use studs if you are planing on using things like NOS, supercharger or a turbo, or even a combination of these like in the NDRA drag cars. Remeber this part is for a VW DOHC motor and just happens to fit our application. Their motors are running turbos or superchargers with NOS. You would also need a MultiLayer Steel headgasket for those types of power adders. I ordered mine from www.chrfab.com

The studs cost more (about 3 times) than bolts but if you want the peace of mind your motor can handle the extra punishment you might dish out, then it's worth it. Just my 2 cents. Jaxx
Here are some pics, sorry about the bad quality I misplaced the cable to my good camera.

chevelle
03-26-06, 09:39 PM
The Northstar head bolts are not torque to yield fasteners. They are recommended to be used only once since they are coated with a microencapsulated thread locking agent that acts as a thread lubricant during assembly and a locking agent once the bolt is installed. There is no practical way to reapply these coatings on the threads and under the head of the bolt so new bolts are recommended when the head must be removed. Otherwise, the bolts themselves are fine.

Torque to yield bolts will stretch permanently when they are properly tensioned. If you measure the bolt, install it and then remove it you will find that it is now longer even when not under load. Those types of bolts cannot be reused as they keep stretching and then break. The Northstar head bolts are not like that despite common rumor.

The Northstar bolt tensioning is spec'd as a torque and angle. Torque and angle provides a much more accurate means of tensioning a fastener compared to a pure torque spec. Just because the fastener is spec'd for torque and angle does NOT mean that it is a torque to yield fastener.

Torque and angle specs even work great on studs as the torque and angle spec, once properly developed, is far more repeatable and accurate than pure torque. Ask ARP.

Any one who thinks that the Northstar head bolts stretched and caused the head gasket to fail is nuts. They didn't measure the bolts originally at the factory so how on earth could anyone suppose that the bolt "stretched" (since they didn't know how long it was originally...) I think they dreamed up this idea of the bolts stretching to explain something and posted it as fact.

Zorb750
03-27-06, 07:52 AM
The Northstar head bolts are not torque to yield fasteners. They are recommended to be used only once since they are coated with a microencapsulated thread locking agent that acts as a thread lubricant during assembly and a locking agent once the bolt is installed. There is no practical way to reapply these coatings on the threads and under the head of the bolt so new bolts are recommended when the head must be removed. Otherwise, the bolts themselves are fine.


:wtf:

Yes they are torque to yield. My Northstar engine design whitepapers and service books say they are.



Torque to yield bolts will stretch permanently when they are properly tensioned. If you measure the bolt, install it and then remove it you will find that it is now longer even when not under load. Those types of bolts cannot be reused as they keep stretching and then break. The Northstar head bolts are not like that despite common rumor.


The stretch need not be measurable after the bolt is removed. You torque it until it stretches, then remove it and it may contract a bit. The stretch may be less than 1mm anyway. Metal does NOT usually usually stretch THAT far before it weakens significantly.



The Northstar bolt tensioning is spec'd as a torque and angle. Torque and angle provides a much more accurate means of tensioning a fastener compared to a pure torque spec. Just because the fastener is spec'd for torque and angle does NOT mean that it is a torque to yield fastener.


Yes it is more accurate, and yes, it doesn't necessarily mean it's a torque to yield fastener if tightening is specified in degrees.



Any one who thinks that the Northstar head bolts stretched and caused the head gasket to fail is nuts. They didn't measure the bolts originally at the factory so how on earth could anyone suppose that the bolt "stretched" (since they didn't know how long it was originally...) I think they dreamed up this idea of the bolts stretching to explain something and posted it as fact.

Yeah, I wouldn't think the bolt would suddenly stretch more after tightening.

chevelle
03-27-06, 04:32 PM
Not sure of your references there but I assure you that northstar head and main bearing bolts are NOT torque to yield. Trust me.

You miss my point about the bolt stretch. When the bolt is torqued/tensioned it stretches, yes. That is what generates the load in the bolt. When the bolt is removed it returns to its original length UNLESS it is a torque to yield bolt. A torque to yield bolt will YIELD PERMANENTLY. In other words, it will stretch quite a bit when tensioned and, when removed, it will now be longer than it was before it was installed. Read up on torque to yield fasteners. This is how they work. If you measure the length of a bolt before installing it, torque it to the correct tension and then remove it and measure it again and it is the same length as it was before then it is NOT a torque to yield fastener. That is what you will find with a Northstar head bolt.

Measuring the bolts when they are installed will tell you how much it stretched during tensioning and will allow you to calculate the load on the bolt based on the bolt metalurgy. That is why critical bolts like ARP rod bolts are spec'd to be tightened until they stretch a certain amount regardless of the torque required.

With the proper ultrasonic equipment the head bolts in the Northstar engine (or any blind bolt in any engine) can be measured very accurately for length with the bolt in place. This is how the correct torque angle procedure is arrived at. Those measurements show over and over that the Northstar bolts are NOT torque to yield as the bolts do not permanently yield .... they return to their original length.