Date: Sun, 13 Feb 2011 19:56:49 -0500
Reply-To: Mike <mbucchino@CHARTER.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mike <mbucchino@CHARTER.NET>
Subject: Re: General engine bolt/nut sizes
In-Reply-To: <4D586C41.5050405@hughes.net>
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These special fasteners are not generally cheap. None of the case fasteners
carry a "one-time use" warning. None of the VW engine fasteners are special
'stretch bolts", either.
They are also not generally re-used several times. Most engines that I've
rebuilt have been used exactly one time, by the factory. And a 2nd time is
no problem.
And most engines that I've rebuilt haven't seen tons of abuse or damage,
those ones don't get rebuilt. They get scrapped.
VW rod bolts are fine for re-use, but the nuts are supposed to be replaced,
due to the flange being staked to lock it into position after torquing.
VW's don't have main cap bolts, but re-usable aircraft-style case tie bolts
with a low torque value. They also don't have head bolts, but reusable head
studs with head nuts that have a low torque value. Only upon engine warm-up
do these fasteners see higher values applied thru the metal's own thermal
expansion or heat growth. None of the VW engine fasteners torque is high
enough to stretch them to or beyond their elastic limits.
Just a clean up and wire wheel of the bolt threads (if not already perfect),
and it's good to go for another million miles. If any thread is worn,
galled, stripped or distorted enough to change the free-running torque above
nearly zero, then you would not want to re-use that bolt. As I said, I
don't see many of those problems on my rebuild candidates. I recommend only
replacing those with another correct good used VW bolt (I have many spares),
or buying new from VW.
The ACVW is different from the WCVW engines, so these rules are specific
to the questions asked for his specific engine.
Mike B.
-----Original Message-----
From: Marc
Sent: Sunday, February 13, 2011 6:41 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: General engine bolt/nut sizes
Fasteners are generally cheap, and there is no way to see if a fastener
is bad or fatigued by looking at it, in most cases. Long ago I learned
the value of using all new fasteners (and the false economy of reusing
old ones). Some fasteners are always one time use, like most torque to
stretch bolts. Some are multi-use. But how can you tell if a fastener
has been reused once too often? With critical fasteners, like rod bolts,
head bolts, main cap bolts, you are risking a lot to save a few bucks.
If it works, great. If it doesn't (and eventually it won't, that's
pretty much a guarantee) then it will cost you big time. Can new
fasteners fail? Sure, but the risks are higher with used. And often the
changes with time/use are not obvious ones, such as changes in torque
specs (thread finish and uniformity has a direct affect on the
relationship of torque to clamping loads for example) or lengthening
that affects fit (such as in blind holes). You pays your money, you
takes your chances.
If a fastener is application specific, buy it from the dealer. if not,
get the same grade generic fastener. Sometimes you can upgrade by going
to a better spec fastener, but a "higher" grade doesn't always mean
better. Sometimes you want a soft, stretchy bolt, sometimes you want a
rock hard bolt. You can't go wrong by matching the original specs unless
there is a known problem (such as with certain rod bolts for example).
As explained, nylock nuts are not suitable for use where the nylon might
get hot enough to soften or melt. Grade C locknuts (all metal grade 8
equivalent) are considered one time use (as is any bolt used with them).
This is because the nut/bolt threads are an interference fit and damage
one another as tightened/loosened. There is more to fastener design than
just thread pitch and hardness. General fasteners often have full thread
or only a short shank. Application specific fasteners often have a sold
shank of a length designed specifically for that application. If you use
a full thread or other non spec shanked bolt instead, you may find the
part or associated components fail because the threading causes
premature wear or fatigue. Sometimes the torque specs can be increased
by using a "higher" grade bolt. Sometimes all that does is lead to the
failure of other parts that could not take the added loads. Generally,
the factory spent a lot of time, money, and engineering brainpower on
the OE fasteners. And generally you are best off to stay with their
choices. You can almost never go wrong using new OE fasteners. Start
changing things, or reuse fasteners, and you just can't say that.
--
Marc Sayer
Journalist, Photographer, Dog Trainer (APDT member #062956)
Board member - Western States Great Dane Rescue Association
Director of Operations& Training - Deaf Dane Rescue Inc.
Oakridge, OR USA
My Homepage - http://gracieland.org
Deaf Dane Rescue - http://deafdane.org
White Danes Yahoo Group - http://pets.groups.yahoo.com/group/whitedanes
Western States Great Dane Rescue Association - http://wsgdra.org
RescueWatchdogs - http://rescuewatchdogs.org
Association of Pet Dog Trainers - http://APDT.com
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