Re-torque head ??

Retorquing is an old habit that's hard to break...and I still do mine.
To check current torque you need to back off the fastener and come up to torque setting. If you achieve the torque at the same position/location then it is still at spec. Your call on whether you want to do them all if a couple check out ok.

Thanks OM for the advice... I'll go ahead and do the re-torque... better safe than sorry.

Pete--do you back off and then come up to the torque because of static friction vs dynamic or maybe perhaps elongation of the head bolt?

Hi Team,
my take on the above discussion is that todays composite materials and the steel shim type gaskets are what is known as Mono-torque gaskets -- ie, one time torque up at instalation only.
The old copper-asbestos type gaskets are re-torque type, ie, re-torque after a few hours of operation. I was always taught at The Dealer to back the fastener - nut/bolt - off about one quarter to one half of a hexagon flat and re-torque. If you wish for interest sake you can mark the fastener position and see where it comes to in relation to your markings after the re-torque.
When the 428B BHL's came out here in OZ I had a programme from Cat of OZ to do the above proceedure on the first few Perkins cyl-heads to see if they were maintaining torque, apparently there had been some issues elsewhere but I found them all to come back to the markings or very close to.
Cheers,
Eddie B.

dependzic

I was always taught that proper torquing was to be done while having the fastener in motion and avoiding static friction. If you try to obtain torque by moving from a static position you will get a false reading from the break away friction. Also want to uniformly load/stretch the bolt/stud.

Don't care what they say, retorquing is a good thing. Gives things a chance to settle out before final tightening. Never lost a head gasket seal and don't intend to.

Seen plenty of so called single torque head gaskets that mysteriously leaked. Usually well after leaving someones shop.

I recall from high school and college physics exactly the point Ole-Magnet has made regarding force to overcome an object at rest as being correct. Makes common sense when you think about a tight or rusty bolt needing to be broken free and once free less force is required to continue the rotation.

Been a heavy equipment mechanic for 20 years and if you do everything right there is no need to re-torque an already stretched bolt or stud.

I really don't like re-using used head bolts, because I have had them break when tightening them to specs. Upon those rare occassions when they must be used, I do so.

On used bolts, studs, and nuts run taps and dies on them and the block. Blow out all dirt, rust and debri from blind bolt holes such as top of block. Do not put any oil in blind bolt holes, there is no place for it to excape to. Oil in a blind hole when tightening a bolt can give you false readings and can even break the block. Oil only the threads on stud, bolt, and nut.

Clean bottom of head and top of block with wire wheel or abrasive wheel used for gasket removal. Lightly do this, don't stay in any one spot long. Clean surfaces with lacquer thinner until rag doesn't get dirty.

For metal gaskets apply copper coat or aluminum spray paint to metal surfaces and gasket. This helps to disperse heat build up and acts as a sealer.

Non-metal head gasket, don't apply anything to them.

Torque setting of used bolts, nuts, and studs; example book specs 120 to 135 foot lbs. Install bolts and draw them up until snug, do not tighten. Set torque wrench to about 75% of torque rating. Tighten bolts according to sequence chart in service manual, if one shown. If non available tighten bolts from center of head outward. Do this equally on the head from out. When finished set wrench for a little less than maximum torque specs, this example 128 to 130 foot pounds. Slightly less than max to avoid breaking one. Tighten in same order as you did before, but be prepared not to bring bolt to full torque. If you feel that you have reached torque and the wrench doesn't click or reading doesn't increase, Stop. The bolt maybe about to break or strip, quit while your ahead. Remove and replace it with new one if it is bolt. A stud you are better off to leave it alone. One stud slightly under specs, won't harm anything. This is a jugdement call. Go over all bolts once again checking for correct torque. You are now done. No need to re-torque.

New bolts or studs and nuts, same example 120 to 135 foot pounds. Same procedure as stated above except final torque is slightly above specs. On this example torque would be 142, 7% above maximum torque spec. Recheck torque and your finished. No need to re-torque. New bolts haven't been stretched and this allows for this.



I

the best advice to this thread is 3TRob's reply. he must read and comprehend the
repair manuals. he understands the importance of bolt stretch and clean fasteners.
i am guessing Rob does not overcharge his customers with unnecessary repairs like
a retorque that is not in the repair manual.

you can be an engineer and re engineer the wheel if that makes you feel better.
caterpillar did not get to be number one world wide by printing disreputable or
bogus repair manuals. it would be a great idea to tear the thing apart every hour
of operation and do a head retorque, completely unnecessary and a wast of time
and energy. follow your repair manuals, cat really does know what they are talking
about. i dont, do not listen to me or anyone else. follow your manual!

I agree basically with the last two posts, make sure everthing is clean, including all threads, to be sure they are free all the way, and tighten to specs, in the late '60's Cat introduced the 'three stage' method which was little more than tightening at final torque a third time. I always used this and would continue going around all bolts, pulling very steadily on the torque wrench in sequence, until the first two in the middle of the head did not move any more. This usually meant going round about five times, but I never had to go back for a re-tighten or repair job. Once an engine has worked, there is no knowing how much friction it will take to move a stud or nut, and loosening cylinder heads to re-tighten always seems madness to me.