Contour Enthusiasts Group Archives Forums Modifications General Mods Masters of the Wrench, technical question for ya!!

I have an automotive technical for all you guru's out there! No, it's not a Duratech question this time so dont kill me! :p ... Anyways, I'm re-torqueing the head bolts on my 87 Supra Turbo as the torque was set *too low* from the recent head job done 5k ago. The head was milled and *new* gaskets (felpro) and head bolts (toyota) were used. The question is, should I *back off* the head bolts before torqueing? Some people say no, as you run the risk of putting to much pressure on the head and run risk of mixing coolant/oil or damaging the head gasket. Others say, it is nessicary to back off the bolts to overcome the *static friction* between the threads of the fastener and the block. Torquing the bolts without releaseing them first will give wildly inaccurate readings and some bolts *may* stay put at the orginal torque value despite the torque wrench being set at a higher torque value.

The orginal torque on the head was 62lbs. With my Craftsman *click* style torque wrench, I used factory torque pattern and set my torque wrench to 72lbs. *Without* backing off the head bolts, only *one* of the 14 bolts budged and all the others clicked indicating the torque was already 72lbs or higher. Do you think that static friction is giving the torque wrench a *false* reading? What is your opnion?

P.S. I realize the head bolts are *torque to yeild* but lab reports using the ASTM A370 tensile test show that these head bolts could be as high as 68 ft. lbs. to 72 ft. lbs. without putting the bolt into the plastic region. In short, the bolts should be fine for re-torque... or so I am told.

If it was my car: I would remove the bolts, clean the sealer off the threads and put them back in. Use new sealer,a nd re torque. If you are careful you will not breeak the seal between the head and block (have you ever pulled a Toyota head without a dead blow hammer?). Reinstall the fasteners with new sealant and re torque.....but that is what I would do
YMMV, void where prohibited by law.....

Torque to yeild bolts should not be reused, at least the Ford torque to yield bolts are not reusable. When they are torqued to yield, they are streched and are no longer usable.

On the Ford system, the bolts are streched beyond use. After torquing to spec, they are turned an additional something like 1/4 turn (the "torque to yield"). Torque to yield is common on engines with iron blocks and aluminum heads.

You best be checking a Toyota shop manual before you go any further.

On non torque to yeild bolts, the threads are to be clean and dry (or at the most, very lightly oiled). The torque sequence pattern in the manual needs to be followed (usually starting from the middle and moving outward). Do not back off when moving to the next torque setting.

JUst use what we used at the Mercedes shop....German torque!Goodentite!
What I would do is not even worry about it,but if you must go buy a whole new set of head bolts,remove and replace them one by one in a scattered pattern.this will keep you from having to worry about the gasket and any mixing of fluids.
Really though after a period of time you cant go back and retorque a set of head (torque to yield)bolts.