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6K views 31 replies 14 participants last post by  chevelle 
#1 ·
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?
 
#5 ·
'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.
 
#7 ·
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.
 
#8 ·
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
 
#9 ·
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.
 
#10 ·
dkozloski said:
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....
 
#11 ·
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.
 
#13 ·
nota said:
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!!!!!!!!!!!!!!
 
#17 ·
Zorb750 said:
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.
 
#19 ·
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.
 
#21 ·
#22 ·
JaxxMan said:
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!
 
#23 ·
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
 
#24 ·
denscor said:
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.
 
#25 ·
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.
 
#26 ·
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!
 
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