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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?
 
#27 ·
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.
 
#28 ·
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.
 
#29 ·
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.
 

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#30 ·
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.
 
#31 ·
chevelle said:
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.

chevelle said:
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.

chevelle said:
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.

chevelle said:
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.
 
#32 ·
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.
 
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