Retorquing tires?!

[Jerome Stanek]

My buddy has a semi with aluminum rims and the maker won't stand behind them if you don't use a special impact torque socket.

[Larry Edgerton]

All this talk about torquing reminds me....I met a fellow who is a superb engineer. Does aftermarket work and analysis of top notch NASCAR engines here. Puts the engine up on a stand in the lab, runs tests, looks @ the oil filter under a microscope, etc, Really cool stuff.

We were talking, and he tells me that when you get down into such fine tuned area as the engines he analyzes, that for torquing, since you also have the lubricants to consider, and the force/friction of the flange/bolt head against the block/whatever, that what they actually measure is the amount that the bolt stretches. I had no idea.

You are correct. If you think of a bolt as a spring you are thinking correctly. On a high dollar engine that costs more than a new car each bolt should be measured for bolt stretch before it goes together and any that do not fall within parameters tossed. ARP built their business on the inaccuracy of normal bolts.

Torque sticks work, but they are not science. They are over torquing the wheel to a somewhat controlled number, so no failures and no snapped lugs. Most shops do it this way, and for most cars/trucks this is just fine. On high performance vehicles I will stick with the torque wrench. Retorquing only takes a couple of minutes.

[Wade Lippman]

Although these are my first new tires on my car, they have had the tires rotated maybe 8 times at several different garages, and no one wanted them checked. Presumably there is no difference between getting new tires and having the old tires rotated. This guy is just showing a bit more caution (or maybe he knows from experience his employees can't be trusted). Is that about it?

In event it is the latter, I suppose I would be negligent not getting them checked.

[Mike Lassiter]

If something bad should happen:
1. if you did NOT have them retorqued that would be their reason for the failure. YOU failed to follow their professional recommendation to have them retorqued. The neglegence is yours and therefore you caused the issue.

2. if you DID follow the "required" retorque, you or another party are now the last hands to touch them and therefore you failed to do it properly. They cannot be held accountable for what others do coming after them.

in the automobile world I don't believe the issue is the cause for concern that some would have people to belief. It was most likely developed by lawyers like all the other standard disclaimers of responsibility.

[Mike Henderson]

You are correct. If you think of a bolt as a spring you are thinking correctly. On a high dollar engine that costs more than a new car each bolt should be measured for bolt stretch before it goes together and any that do not fall within parameters tossed. ARP built their business on the inaccuracy of normal bolts.

I used Larry's message for this question but the question is to anyone who knows. How do you measure bolt stretch when you're torquing a bolt? On something like an engine head, the bolt is fully buried in the engine - that is, you don't have access to the end of the bolt. So how do you measure stretch?

Or am I missing something?

Mike

[Mike Lassiter]

rod bolts often are tightened with a special tool that allows measuring the stretch while tightening using a dial indicator. Those you mention would be torqued to a value or angle torqued which is tightening to a specific torque, then turning an additional number of degrees to give the stretch like the head bolts. torque to yeild or angle torque are the same thing just different wording.

[Larry Edgerton]

I used Larry's message for this question but the question is to anyone who knows. How do you measure bolt stretch when you're torquing a bolt? On something like an engine head, the bolt is fully buried in the engine - that is, you don't have access to the end of the bolt. So how do you measure stretch?

Or am I missing something?



Mike

The bolt is measured before and after it is torqued in a fixture before the engine is assembled.

[Ole Anderson]

Working on my son's Saturn Astra (Opel) some of the rear suspension's bolt torque spec said 87 ft-lbs + 45 degrees + 15 degrees. Never ran across that before.

[Larry Edgerton]

Working on my son's Saturn Astra (Opel) some of the rear suspension's bolt torque spec said 87 ft-lbs + 45 degrees + 15 degrees. Never ran across that before.

.


Its becoming fairly common on production cars and has been used on race engines for years. The 87 pounds is to the theoretical point that will start to stretch, and the 45 degrees is the amount of stretch that they want. It is supposed to be a more accurate way