Re-torquing head question on twin cam

[vteuropa]

I want to re-torque the head on my TC. I found the specs which indicated 60-65 lb cold. It didn't mention if that was wet or dry. Also am curious as to sequence.

Thanks in advance.

[BDA]

Normally, torque values are dry values unless specified otherwise. When retorquing, you want to go by the sequence, loosening the bolt and then tightening it to spec (as you note, 60 - 65 ft-lbs). You need to loosen the bolt first because of the difference between static friction force (effort to move something at rest) and dynamic friction force (effort needed to continue movement).

Here is a snippet from the TC workshop manual that gives the torque sequence.

[jbcollier]

One at a time.  Mark each fastener's position.  It has to at least end up in the same position.  Check the timing chain tension and, if adjusted, check the ignition timing as well.

[vteuropa]

Excellent, thanks all for the answers.

[BDA]

It has to at least end up in the same position.

I'm not disagreeing with this, but what would you do if a bolt didn't at least end up in the same position? Would you assume the head was warped?

[4129R]

It could be because the bolts have stretched.

If you think of 1 complete turn of the bolt = the thickness of 1 thread on the bolt. If the thread is UNC, and say the thread is about 1/16" across, then each 10' of turn of the torque wrench equates to 1/36th of 1/16" = 1/576", which I make about 2 thou.

My numbers may be completely wrong, but I think my theory is correct, in the fact that a significant amount of turn on the torque wrench equates to not a lot of movement of the bolt/head/gasket.

Here is the threads per inch chart, so I wasn't too far out.

http://www.carbidedepot.com/formulas-tap-standard.htm

[BDA]

Good point, 4129R! I'd heard of being concerned about rod bolts (and maybe main bolts) stretching. In fact I think I remember that in the past some would determine the proper tightness of a rod bolt by how much it stretched (or maybe they would determine whether it was good any more ?), but I didn't consider head bolts would stretch. Since I never bothered to check that, I don't know, but I would think it would be a rare occurrence. Thoughts?

[jbcollier]

No, you would assume that there is an issue: excess friction, torque wrench, etc.  Speaking of friction, the bolt heads and washers should be lubricated.

Most "older" engines have head bolts that stretch very little and able to be reused over and over again.  These engines typically require the head bolts to be re-torqued at least once after the head has been disturbed.  Newer engines use special bolts designed to stretch quite a bit and do not have to be retorqued.  They are also single-use.

[Grumblebuns]

I have a junk TC head that was warped. One thing that is instantly obvious is the amount the head bolt washers have recessed into the head surface. Did TC heads ever have a hardness issue?

In torqueing the head bolts, is there any benefit to applying oil under the washer to keep it from rotating as the head bolt is torqued or am I being overly cautious?

Joji Tokumoto
Fallbrook, Ca

[jbcollier]

Bolt heads and washers should be lubed.

[BDA]

I have never heard any reference to lubricating just the bolt head and washer. The reduction of friction by lubricating the bolt head and washer while using dry torque values would increase the stress on the bolt, but given whom I'm hearing this from and considering that the contribution to the total friction from the friction between bolt head and washer would probably be small relative to that from the threads when tightening the bolt, it sounds like a a good idea.

[jbcollier]

The block's cast iron has some natural lubricity for the steel bolt.  The steel on steel of the bolt head and washer does not and they will gall sometimes without lube.