VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 Understanding stretched bolt threads

Hello All,
With the recent discussion concerning original head bolts and wether they may have threads that are stretched or not, what are the effects concerning the bolt itself and concerning the engine block threads? If the bolt threads stretch, is there also block thread stretch? Can the block stand up to torque pressure better than the original bolts? Also, when replacing old for new head bolts, would using anti-seize compound be recommended? Is working from the center outward using even pressure up to 70 ft lbs in increments be reasonable for head torque, considering smooth surfaces and new gasket. When would it be advisable to re-torque head after initial installation?

In the later shop manuals Chevrolet recommends oiled threads. I would also clean the the threads in the block with a tap.

Anti-Seize works great on the bolt threads as well.

I do no believe the threads in the block will stretch but rather the area on the bolt just above the block mating surface. Checking that area with a magnifying glass view the outer edge of the thread. If it is ragged and cracked then the bolt has stretched. Proper tightening sequence is important so follow the shop manual recommendations and starting in the center and working outward is the usual method. Lubricating the threads with oil or anti-seize is a good practice-just don't over do it- a thin coat is all it needs. Not sure of the proper mileage (check your manual)to re-torque the head but when doing so check other bolts such as manifold and exhaust. Any that are subject to heat and expansion and contraction could loosen after initial assembly.

The area around the taped hole in the block can raise up some. If not decked I run a large flat file on the block. If working on an engine that the tap hole goes into the water galley, I use permatex on threads.

These are some of my bolts seeing daylight after 30 years in the dark. The ones on the pass side look oily and fairly smooth. Their twins on the manifold side look pretty beat, all rusty, dried out. Must be that hotter, harsher environment.
The only thing I'm examining closer right now is a beer.

pass side


manifold side