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Old April 24th 17, 02:53 PM posted to rec.bicycles.tech
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Default torque wrench issues

On Sunday, April 23, 2017 at 5:19:49 PM UTC-7, wrote:

Torque specs vary considerably by application. Some are given as
clean and dry, some are given as lubricated with oil - some are given
cold, and others hot. That said, I personally have never run across a
torque spec that was so "close to the edge" that torqing with "stray
lubrication" would cause immediate failure of the bolt by twisting off
the end.
However, that said, most of my wrenching has not been on bicycles but
on automobiles and agricultural and construction equipment which may
be slightly more "overengineered" or "overbuilt"
Also, some of the wrenching I have done on bicycles has revealed some
terribly poor quality materials (can anyone say "flying pigeon"?)

There have been tests done which indicate oiled threads do not affect
bolt tension and give the most consistent torque /tension results
(10W40 oil).Anti-sieze can increase the tension on a bolt by up to 71%
at the same measured torque.
Moly paste used as a lubricant was somewhere in betweeen - but
antiseize was non-linear in it;s results as the friction of the
threads did not increase with the tension on the bolt.

See http://benmlee.com/4runner/threads/threads.htm for the complete
results.

Even the difference between a cadmium plated bolt, a shiny zinc
plated bolt and a black oxide finished alloy bolt can be measured and
MAY be more significant than the difference between oiled and dry.
Also the existance or non-existance of a washer under the head of the
bolt or the nut can affect the tension on a bolt at a given torque -
or even the difference between a mild steel or a hard washer.

For a VERY accurate "torque spec", the rod bearing bolts, for
instance, on a high performance racing engine, are torqued to a
pre-determined stretch. The bolt is measured before installation, and
then is torqued until it measures a precise amount longer than the
initial measurement. This requires precision bolts - and the bolts
MUST NEVER BE RE-USED.
Under torquing (insufficient stretch) on these bolts will cause the
bolts to break in use.

I'm not aware of any "torque to yield" bolts in use on bicycles.


Now that you mention it I do remember that on cars, way back when, you would torque them them to a low setting and then run the engine until warm and then torque everything down to prevent the BMW problem of blowing off head bolts from heat expansion causing the yield of the head bolts to be exceeded.

It seems to me I can even remember engines blowing head gaskets if you didn't follow these procedures.

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