[AT] Torque for bolts vrs studs in cylinder heads?--followup

[Jim & Lyn Evans]

It is not done because they wanted to use smaller or cheaper bolts.  What
you really want is a specific clamp load on the bolt.  The torque really
doesn't matter.  The problem is it is nearly impossible to measure clamp
load, but fairly easy to measure bolt torque.  Friction is a big part of the
torque measurement and the friction torque does nothing to help your clamp
load.  The amount of friction varies widely because of oil, dirt, etc. To
help make the clamp load more consistent is why in a lot of applications
they use the torque-turn method.   You torque to smaller amount and then
turn the bolt a set amount farther. The bolts that yield also help make a
more consistent clamp load.

Jim Evans


-----Original Message-----
From: at-bounces at lists.antique-tractor.com
[mailto:at-bounces at lists.antique-tractor.com] On Behalf Of charlie hill
Sent: Saturday, April 28, 2007 1:32 PM
To: Antique tractor email discussion group
Subject: Re: [AT] Torque for bolts vrs studs in cylinder heads?--followup

John,  some of the new light weight auto engines use head bolts that are
"torque to yield"  which means they are tightened to where they are just at 
the point of failure.   When you remove the heads on those engines you MUST 
replace the head bolts.  Those first GM diesel car engines (the 5.7 built
from a gasoline block) were that way.

In other words they used the smallest, lightest head bolts they could get by
with and they won't stand up to being re-used.

Charlie


----- Original Message -----
From: "John Wilkens" <jwilkens at eoni.com>
To: "Antique tractor email discussion group" <at at lists.antique-tractor.com>
Sent: Saturday, April 28, 2007 1:22 PM
Subject: Re: [AT] Torque for bolts vrs studs in cylinder heads?--followup


> Many thanks guys for educating me about head bolts!   To be sure,
> I'll stick with studs!    John W.
>
>
>
> At 08:08 PM 04/27/2007, you wrote:
>>
>>John, There are a whole bunch of GOOD reasons to stay with all of the OEM
>>parts and torque specs on head bolts! You may get away with some
>>non-OEM parts
>>sometimes but it is like gambling with your engine's life span. Granted it
>>varies from engine to engine, usually older engines have more room
>>to play with
>>and more modern engines have tighter specs with almost no room for error.
>>Some  head bolts are TTY and can only be used once. The headgasket
>>thickness also
>>  matters on some engines especially if you have had the head resurfaced.
>>Sometimes the OEM manual will give 2 torque specs with the head bolt
>>dry or oil
>>on threads. Studs or bolts of the same grade should be the same spec I 
>>think.
>>If  you lower the grade of bolt you may be asking for problems. Just my 2
>>cents.  Willard Smith, Tacoma, WA.
>>
>>About how much more torque would be required for using bolts in an
>>engine head vrs. the regular studs?  (One for the  experts!)   John W.
>>
>>In the wide-open spaces of NE  Oregon
>>
>>
>>
>>
>>
>>
>>
>>************************************** See what's free at 
>>http://www.aol.com.
>>
>>_______________________________________________
>>AT mailing list
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>
>
>                    In the wide-open spaces of NE Oregon
>
>
>
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