Head re-torque debate

[SIVAllan]

Correct. Simply ensure that the wrench is at the correct setting, put it on and twist until it clicks (or reaches the proper setting if a dial type). Usually after a few hours following the initial torquing the wrench will turn a fraction before the click.

By the way, torque wrenches, especially cheap ones, can be inaccurate, and in any case even a good one can change its characteristics with time and use. It's a good idea to check it against a known accurate one, or if you aren't certain that even the other one is accurate, against two others (to average out any error).

Shop guy said to ALWAYS set a clicker torque wrench back to Zero when not in use, or it will loose accuracy.

We've been working with my wrench which was not cheep, but is a 4% wrench. I had no luck finding a 2% wrench locally.

Allan

 

[sunbby]

Stiction is a threshold, not a continuous force. However, the act of moving the fasteners in order to reach the desired torque setting by definition is measuring dynamic friction and stretch, so I see no reason to back off and retorque to overcome stiction.

Nick, I think you described the exact argument for backing off before retorque. For example, a torque spec of say 50 ft-lbs would be measured while turning the bolt or nut. When 50 ft-lbs is reached a clicker type wrench "clicks". It will now take more than 50 ft-lbs to get the nut turning again.

Now imagine the bolt tension reduces for some reason; but not enough to reduce the torque needed to overcome the static friction to a value below the torque spec, that 50 ft-lbs. In this case the wrench will click immediately, without turning the nut at all and you have not regained the desired bolt tension. If you back off and "start over" you will then measure the dynamic friction induced 50 ft-lbs, which will undoubtably be past the previous point.

 

[Jim E]

Just do not get a warm fuzzy backing off a fastener holding down a head gasket. I could see where imperfections on the washers could cause a bad reading though.

 

[Nickodell]

Todd: Stiction is the product of the coefficient of friction, compressive force between the meeting surfaces, and area of contact. As the area under a nut or bolt head is small, the increment due to stiction over dynamic friction is tiny, especially when washers are in use, and probably less than one lb/ft. - well within both the margin of error in the design of the assembly and the errors of the wrench. You're agonizing over a nonexistent problem.

 

[sunbby]

Todd: The increment due to stiction over dynamic friction is tiny, especially when washers are in use, and probably less than one lb/ft. - well within both the margin of error in the design of the assembly and the errors of the wrench. You're agonizing over a nonexistent problem.

Yes, I doubt it is really a problem too, but theoretically it could be an issue. And if the bolt turns when you retorque, as Jim said it usually does, it is a moot point.

I also agree with Jim, just doesn't seem right to back off on a head gasket, especially if you've sprayed on copper coating and such.

 

[jumpinjan]

Try to keep this going about head gaskets & head re-torque. the rest of it was moved.

 

[Pumpkin]

Shop guy?

O K OK,, I have been gone for a while. Did I miss something on TV? Or do we have a newby on by the name of Shop Guy? I've read several posts that mention this one.
Hmmn
Chuck

 

[SIVAllan]

O K OK,, I have been gone for a while. Did I miss something on TV? Or do we have a newby on by the name of Shop Guy? I've read several posts that mention this one.
Hmmn
Chuck

The SIV went into a shop that has opinions. A couple of those have been expressed here, for comment if interested. The shop remains unnamed but has been referred to as shop guy.

Alan