[s-cars] Yet More Bolt Scientology

[Bill Mahoney]

Guys
Yes there are bolt scientists and to prove list genius, even they can only
offer an "opinion."
It's prolly fair to say it's an educated opinion.
Cheers'
Bill M
95 1/2 Avant -fast, musical and non studded
75 Carrera


-----Original Message-----
From: Bill Eccles [mailto:Bill at boltscience.com]
Sent: Tuesday, October 29, 2002 2:01 PM
To: bill mahoney
Subject: Re: Ask a question of Bolt Science


Bill

Thanks for sending us a question via our 'Ask a Question' feature on our
website.

Sorry for the delay in answering your email.

Obviously what follows is my opinion.

The advantage of a lubricant/anti-seize compound is that more consistent
friction values should be provided giving a more consistent torque-
tension relationship. Also there should be less wear on the threads and
so should last longer in an application like yours.

There are three basic methods for the checking of torques applied to
bolts after their installation; namely, taking the reading on a torque
gauge when:

1. The socket begins to move away from the tightened position in the
tightening direction. This method is frequently referred to as the
"crack-on" method.

2. The socket begins to move away from the tightened position in the un-
tightening direction. This method is frequently referred to as the
"crack-off" method.

3. The fastener is re-tightened up to a marked position. With the
"marked fastener" method the socket approaches a marked position in the
tightening direction. Clear marks are first scribed on the socket and
onto the joint surface which will remain stationary when the nut is
rotated. (Avoid scribing on washers since these can turn with the nut.)
The nut is backed off by about 30 degrees, followed by re-tightening so
that the scribed lines coincide.

For methods 1. and 2. the breakloose torque is normally slightly higher
than the installation torque since static friction is usually greater
than dynamic friction. In my opinion, the most accurate method is method
3 - however what this will not address is the permanent deformation
caused by gasket creep. An alternative is to measure the bolt elongation
(if the fastener is not tapped into the gearbox). This can be achieved
by machining the head of the bolt and the end of the bolt so that it can
be accurately measured using a micrometer. Checking the change in length
will determine if you are losing preload.

The torque in all three methods should be applied in a slow and
deliberate manner in order that dynamic effects on the gauge reading are
minimised. It must always be ensured that the non-rotating member,
usually the bolt, is held secure when checking torques. The torque
reading should be checked as soon after the tightening operation as
possible and before any subsequent process such as painting, heating
etc. The torque readings are dependent upon the coefficients of friction
present under the nut face and in the threads. If the fasteners are left
to long, or subjected to different environmental conditions before
checking, friction and consequently the torque values, can vary.
Variation can also be caused by embedding (plastic deformation) of the
threads and nut face/joint surface which does occur. This embedding
results in bolt tension reduction and affects the tightening torque. The
torque values can vary by as much as 20% if the bolts are left standing
for two days.

In an application that involves repeated re-intallation - my opinion is
that studs and nuts can be a better option since this provides
opportunity to replace worn threads.

One last thought - have a look at the fastenertechnology.com website for
a new type of nut that may be helpful in your application. The Shur-Lok
nut allows very quick installation over worn and damaged threads.

I hope that this helps.

If you need any further clarification on the above or other information
related to bolted joints, please do not hesitate to contact me.

Best regards


Bill Eccles
Bolt Science - Providing expertise in Bolted Joint Technology
Visit our website at www.boltscience.com
Telephone +44 (0)1257 411503   Fax +44 (0)1257 411650



In message <E1844Q4-0007c7-00 at uk-0-a.www.demon.net>, bill mahoney
<wmahoney at disk.com> writes
>Below is the result of your feedback form.  It was submitted by
>bill mahoney (wmahoney at disk.com) on Tuesday, October 22, 2002 at 20:10:24
>---------------------------------------------------------------------------
>
>company: S-Cars.org
>
>question: Our Audi S Car Organization has an ongoing debate with reference
>to proper wheel bolt tightening and torque procedures.
>Specifically during a track event,
>Should anti seize compound be used? Ever?
>How should torque be checked when wheels are hot?
> i.e. Loosen then re torque?
>Is it better to convert to studs and nuts?
>Is one type of nut or bolt better than another for locking the
>wheel in place?
>It seems everyone has an opinion, so perhaps your organization may
>lend us some scientific input?
>Thanks much!
>Bill Mahoney
>wmahoney at disk.com
>
>
>
>
>---------------------------------------------------------------------------
>