Well, the head gasket has been replaced, the head retorqued, and all is well
(almost - the valve cover gasket is weeping a bit).
I had asked the proper routine for re-torquing the head, and weather it was
necessary to first loosen each net prior to retorquing. Someone replied
that this wasn't necessary, and wondered why this would even be considered.
I still can't say it is necessary, but here is the logic behind it.
Fastener clamp load is what we are after. Torque settings are the typical
methods used to ensure that appropriate levels of clamp load are developed.
There are many factors which also affect clamp load - thread forms,
lubrication, etc. (i.e. a lubricated thread will develop a significantly
higher clamp load for a given torque). All fasteners also have a
"break-away" torque, which requires a higher apparent torque to overcome,
but that has no affect on clamp load. Hence, with a torque wrench, to get
accurate reading, the fastener should be rotating. You back the nut off a
bit, then torque with a smooth rotation.
I spoke with John Twist on this as well. His method is as follows:
Loosen the valve cover bolts. Run the engine to operating temp, and shut
off. Slacken the head nuts until loose (in order). Lubricate each stud
liberally. Torque to 50 ft.lbs. in graduated steps, following the proper
order. He performs this procedure immediately after installing a new head
gasket, and said that he does not feel it necessary to repeat the process.
FWIW-
Chris Delling
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