Head bolts have always been overlooked on the level of importance, but have played a major role in constant head gasket failure through out the entire production days of the 5.7L Diesel. The head bolts on the early engines had major problems, stretching and sometimes, and most of the time, literally breaking. These bolts would break by either popping the top of the bolt off or breaking in half completly...either way, this would cause that area in the head to loose its clamping force, and naturally, the head gasket would leak...Just imagine installing the heads and forgetting to put one of the bolts in...same thing. At this point, when repairing the engine, only the broken bolts where replaced, others, including the stretched ones that where overlooked, were re-used...which would probrably work just fine on a gas engine..but not this engine. Everyone scratched their heads when the same engine returned 15,000 miles or so later with a blown head gasket.
Some of the joys that go along with running an engine with stretched bolts is the surface of the cylinder head becoming irregular...or in other words, warped. This is explained more thouroughly in the Cylinder Heads section...so back to the head bolts...
In 1982, the head bolts where updated by GM, but still werent any better, the same problems occoured. As GM Goodwrench began remanufacturing the 5.7L Diesel in 1983, the head bolts where again updated...and the problem of snapping bolts seemed to go away...The head bolts would hold torque fairly well untill the timing was advanced to try to achieve better performance. The bolts would then stretch, and the head gasket would eventually fail..but then again, the engine was regasketed and the heads torqued down with the same stretched bolts, that appeared to be ok...
It is very important that the head bolts are measured..they should all be the same length. If any are longer then others, then it is infact stretched, and is probrably the reason of head gasket failure. An engine running after it has stretched a bolt would be the same as loosening one head bolt and running the engine.
I dont suggest the use of OEM head bolts for the 5.7L Diesel, but if you must use them, then be sure to replace them all at the same time..even if they appear and measure out to be ok. The head bolts are supposidly TTY (torque to yeild) bolts..meaning that the bolts cant be re used and should all be replaced in the event that the cyliner head is removed.
To prevent head gasket failure, the timing must not be advanced more then 2 degrees over stock when running with OEM head bolts.
To see the aftermarket options for head bolts for the 5.7L Diesel, see the 5.7L Performance section.