Date: Wed, 28 Sep 2011 01:18:03 -0500
Reply-To: Tom Hargrave <thargrav@HIWAAY.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Tom Hargrave <thargrav@HIWAAY.NET>
Subject: Re: Torque Specs - Lug bolts and nuts
In-Reply-To: <00ff01cc7da0$01635c30$6401a8c0@PROSPERITY>
Content-Type: text/plain; charset="us-ascii"
This discussion reminds me of when I worked at Browns Ferry Nuclear Power
Plant.
The facility has three BWRs, Boil Water Reactors for those not familiar with
BWR.
Anyways, each reactor primary containment vessel has a 11 ton lid that's set
on top & fastened all the way around with 6" diameter stainless steel nuts
that spin down onto protruding threads. Some also call it the "tea kettle
lid" for obvious reasons.
Then they go through a torque procedure that lasts for days with a dial
indicator type torque wrench so large that it takes two strong men to lift
it. "From memory" the final torque is 150 ft lb and when this is done each
nut is tightened EXACTLY 90 more degrees.
Also the nuts are so close together that there is just enough room to put
the torque wrench on one without touching the others.
And BTW Cherbobyl is a BWR plant but they had and still have no redundant
safety systems. We do and Nuclear Power is safer here than coal power.
Thanks, Tom Hargrave
www.stir-plate.com
www.towercooler.com
www.kegkits.com
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@GERRY.VANAGON.COM] On Behalf Of
Scott Daniel - Turbovans
Sent: Wednesday, September 28, 2011 12:32 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Torque Specs - Lug bolts and nuts
you always bring things up in steps...
like on head bolts.
what steps are should be used is often specified.
the waiting overnight to torque 928 headbolts , could have been about
letting the head gasket settle..
and not about the bolts so much.
were they stretch head bolts, or non-stretch type ?
but yes..always in steps, that's only logical and natural.
especially when it's multiple fasteners in a group.
like on a cylinder head say.
----- Original Message -----
From: "Don Hanson" <dhanson928@GMAIL.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Tuesday, September 27, 2011 9:33 PM
Subject: Re: Torque Specs - Lug bolts and nuts
> On Tue, Sep 27, 2011 at 8:51 PM, Gary Bawden
> <goldfieldgary@gmail.com>wrote:
>
>> Snipped.
>>
>> I believe the engineers know this, and set torque values to a number that
>> they believe will do the job, without over-stressing the part. And as has
>> been pointed out by others, it's the uniformity of torquing fasteners (at
>> least on parts having more than one) that is probably more important than
>> the actual torque value.
>>
>
> One thing to keep in mind about torquing something to specs....Depending
> on the parts connected by the torqued nuts, bolts, studs, whatever....they
> should often times not be taken right to the specified torque, all in one
> tightening. When I do alloy wheels up to 100lb/ft....I go round to about
> 80 in a star pattern, then I re-set the wrench and do it up the final
> 20lbs.
>
> My engine mechanic used to take two full days to torque the heads on the
> 928 motor....he would (I don't have exact numbers) torque em up to about
> 50%
> and leave em all day, then come back and go to like 80% and leave em
> again.
> then again with a 'resting, settling period' and finally go to full
> torque...
>
> Castings seem like they are pretty brittle, somewhat fragile...If you are
> to torque say a water pump to (out of thin air, this figure) 30ft/lbs....I
> wouldn't feel right just doing it up, one fastener at a time, right to
> 30lbs...I'd probably snug it up, then torque to 20, then go back and go at
> it with 30ft/lbs....minimize and spread the stress.
-----
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