I posted this some time ago about ARP or Toyota head bolts (not studs). Newer ARP head bolts come spec'd for 90ft lbs... refer to the manufacturer's specs for your bolts of studs (if Toyota, 75ft lbs is within spec for that size fastener and materials).
Quote:
Originally Posted by cre
Stock is 58 ft lbs. The recommended torque for our size head bolts with aluminum heads is 72 or 75 ft lbs. Studs are torqued to about 90, IIRC. BOTH values vary depending on what lubricant is used for the install. I only remember some of the reasons for the differences so I'm not going to try to get in depth with this as I'd just be guessing at the end.
A retorque is good medicine for any new fasteners or gaskets (especially composite gaskets). You need to back off the fastener anywhere from one quarter of a turn to up to a full turn... you don't want to over do it though, just enough to free up the fastener. Then retorque to spec. If striction is encountered back the fastener off a little more than the first time and then torque again. When torquing ANY type of fastener you want the fastener to move smoothly and steadily the whole way... striction can cause big variances in torque readings. Also, when backing them off it isn't a bad idea to back them all off and then retorque uniformly.
As long as you properly tend to the threads in the block, lubricate with a high grade lubricant (not just one that claims to be good  ) and retorque PROPERLY either type will contribute to a seal which may very well out live the car; Depends on how well everything else was tended to.
Studs do allow for a higher clamping force (accuracy is more to do with the installer IMO) and definitely gives you a better piece of mind (especially with certain types of head gasket construction).
Quote:
Originally Posted by oregonjoe
I have wondered if you can torque down a composite gasket too much? to a point that the crush rings expand too much into the coolant and oil passages? Don't think metal head gaskets have the same issue.
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Not really, no; Not at this level of torque. I've gotten that answer from people much smarter than I. It is possible to compromise an old composite head gasket with too much pressure after a retorque, but whether that's what the cause of a BHG after a retorque or if the gasket was already blown prior is too difficult to say. |
EDIT: You can compromise an old HG by torquing As for how often it happens... hard to say. The persons HG may have already been on the way out and the retorque made it worse or earned them another 5000mi OR the retorque may have been entirely to blame.