3.1 MPFI head bolt torque spec question

[Guest TurboSedan]

i just got my TGP cylinder heads back from the machine shop. i am using new Fel-Pro head bolts and Fel-Pro 9471PT head gaskets. my Haynes manual says to tighten all of them down to 33 ft/lbs in sequence, and then and additional 1/4 turn in the same sequence. well i torqued them down to 33 ft/lbs, but before i tightened the bolts another 1/4 turn i adjusted my torque wrench to 90 ft/lbs (i wanted to see if 1/4 turn was enough to reach 90 ft/lbs). well the first head bolt i turned it exactly 1/4 turn when the torque wrench clicked indicating 90 ft/lbs. the same thing happened on several head bolts; right at 1/4 turn past 33 ft/lbs the wrench would reach 90 ft/lbs. soooooo....i went ahead and tightened all of the head bolts down to 90 ft/lbs.

 

does this sound right or is 90 ft/lbs too tight? it seems to me that 1/4 turn past 33 ft/lbs = 90 ft/lbs....

[Regal_GS_1989]

When I replaced the heads on my regal, that is exactly what I did. Except, I used and angle gauge on my socket to find 90*

[DaveFromColorado]

Torque to yeild bolts will stretch to make their max holding force, it's the point just before they break.

 

the thing is, you aren't looking for the holding force in this situation, you are looking for an exact distance between the block and the top of the bolt, and the bolt will* stretch, where on average they will reach a certian force needed to turn (as seen on your torque wrench) but that's not always the correct distance, and you may "over-stretch" or even "under-stretch" your bolts, in which case, you'll have a weak spot somewhere across your head.

 

that's also why you cannot reuse these bolts.

 

--Dave.