Re-torquing heads

[raz]

When and why would I want to re-torque my heads? Some seem to have the opinion it should be done whenever checking the valve clearance and possibly when topping up fuel . I can understand it could be needed some time after replacing the foot and/or head gasket, but otherwise I don't get why it would be needed at all.

 

Another thing I've read is that you don't just re-torque, but first you loosen all the nuts. That's where you lose me completeIy. Why would I want to do that? Is this something everybody agrees on or is it disputable black magic that will make this a long thread of healthy arguing?

 

 

EDIT: Ouch, I forgot to search the forums. It's all in there already, it seems.

[Greg Field]

On a new bike, if it were mine, I'd re-torque and re-set the valves after the first day or a few heat cycles. I'd check it again at the 600-mile service, and then I wouldn't worry about it again.

[Guest Gary Cheek]

Ditto

[pete roper]

I have a feeling that when they are torqued at the factory they actually over-torque them, there was a rash of broken studs a few years ago which might of been related to this but for whatever reason I've never felt it neccessary to retorque the heads on a *new* bike and certainly when you try to loosen the nuts on factory fresh heads the seem to be a damn sight tighter than 32 ft-lbs.

 

On rebuilt motors I do as Gary and Greg. Heat cycle the engine and let it cool completely, re-torque, then repeat at first service (Approx 800km/500miles.) then forget about it until the heads come off again.

 

Withe the *new* twin plug motors the head and base gaskets are incompressible steel rather than the earlier kingerlite type which will initially compress in service so I don't see any need to ever re-torque these.

 

As to why do you back off the nuts before re-torquing? Sliding friction is less than static friction. Try pushing a heavy object across a floor. It needs a good shove to get it moving but then considerably less force to keep it moving. Same with nuts and bolts on or in threads. The nuts should be backed off and the threads lubricated prior to re-torquing to ensure that the nut can move freely before reaching it's torque point. The lubricant also elps overcome friction on the thrads which will interfere with the clamping force exerted by the fastener.

 

Pete

[raz]

As to why do you back off the nuts before re-torquing? Sliding friction is less than static friction. Try pushing a heavy object across a floor. It needs a good shove to get it moving but then considerably less force to keep it moving. Same with nuts and bolts on or in threads. The nuts should be backed off and the threads lubricated prior to re-torquing to ensure that the nut can move freely before reaching it's torque point. The lubricant also elps overcome friction on the thrads which will interfere with the clamping force exerted by the fastener.

 

Pete

It was the "loosen all before torquing any" I didn't get. Now you say lubricate the threads, and some say loosening just one nut could warp the head so OK, I get it. It would be hard to lubricate the threads after just backing off the nut 1/4 of a turn... Not that I think loosening one nut would warp these heads but I surely don't want to be the one telling you from first-hand experience it actually happens...

Thank you all

[Guest ratchethack]

Raz, not sure if I can add much of anything here, but that ain't stoppin me . . .

 

Just to clarify, y'unnerstand. . .

 

Loosening one head nut fully by itself can, has, and will warp many kinds of heads, and I'd never consider risking it on any kind of cylinder head, even though there are probably certain kinds of heads where you could get away with it without damage.

 

Whenever heads are removed, each nut or bolt is backed out gradually, in series , following a cross-head (or with multi's, a spiral pattern always specified by the mfgr. service manual) to ensure the head will not be stressed to the point of warping. As a rule of thumb, I make it a 3-step process, going about 1/8 turn on each, then start over for the next pass -- I do the same thing when bringing a head up to torque in the tightening process, setting torque to two intermediate settings on the way up to full torque.

 

The only proper way to torque nuts or bolts is to use a thread lubricant as Pete has stated. This ensures a full and uniform tensile pressure at each stud or bolt.

 

At 10K mi., on the Guzzi, I loosened each head nut gradually, in cross-head pattern (not forgetting the "buried" socket-head nut under the cover in the most inboard position) until all were finger-loose. Since they were "automatically" all lubed with pooled-up oil under the rockers and rocker shaft at this point, there was no point in lubing the already-lubed threads, I just followed standard cross-head tightening procedure and brought them up to spec. as described above.

 

BTW - gauging "by feel", when loosening before re-torquing, there were a few on each head that were significantly of lower previous torque than the others. I reckon the effort was well worth it.

 

BAA, TJM, & YMMV