HEAD BOLTS

[douglasduncan]

I talked to an engine remanufactur today and was told they have had success using ridged head bolts and not the factory. They told me that the heating cycle eventually allows the bolts to strech and loosen and that is why the threads go bad.

Any insight??

[mikeal1892]

I could kinda see this happening

Michael -

[acklac7]

This same topic came up over at cadillac owners....Someone appeard to have the answer....

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.

[jhall]

acklac7,

Something is in my head that the caddy guru once said these were torque-to-yield. Maybe I thinking of something else, but I thought it was the head bolts..

Anybody else got a better memory?

[acklac7]

This is one of those times that I can say, with absolute certainty, that the above quote is correct...Lets just say the "force" is with me

[Ranger]

Acklac,

I fully understand "the force", however, I am with Jhall. I could swear I remember him saying that they were torque-to-yield. Infact, that is the first thing that came to my mind when I originally read the above post. If anyone can find an old post one way or the other it is BBF. "Your mission, should you decide to accept it"......

[zonie77]

Acklac,

I fully understand "the force", however, I am with Jhall. I could swear I remember him saying that they were torque-to-yield. Infact, that is the first thing that came to my mind when I originally read the above post. If anyone can find an old post one way or the other it is BBF. "Your mission, should you decide to accept it"......

I'm sure he said that to me when we goofed up installing some (got interuppted and weren't sure where we were). He may not have said they were, but I don't think he said they weren't when I asked.