[Mgs] loctite question - (Mgs Digest, Vol 68, Issue 5)

[Clayton Kirkwood]

That's interesting. But so often the stud or bolt in similar applications
gets chemically welded in - rusted. Nuts the same way. So, should the
threads be coated with an anti-seize or oil, or should they be "dry"? I
don't think loctite works very well with any anti seize.

Clayton



-----Original Message-----
From: mgs-bounces at autox.team.net [mailto:mgs-bounces at autox.team.net] On
Behalf Of Barney Gaylord
Sent: Tuesday, January 08, 2013 6:41 AM
To: Glenn Schnittke; mgs at autox.team.net
Subject: Re: [Mgs] loctite question - (Mgs Digest, Vol 68, Issue 5)

The answer for seating torque on the stud (any stud) is finger tight, not to
exceed 5 lb-ft of torque.

The recpetical is a deep threaded hole, and the stud has a shorter thread.
The stud screws in until it runs out of threads on the stud, at which time
the last incomplete thread on the stud will bind in the first thread on the
receptacle.  Applying more torque at that time will damage the top female
thread, raising a burr and possibly damaging a casting.  Too much torque on
the stud could crack the casting.

Most studs (not all) will have course thread on the bottom end and fine
thread on the top end.  The steeper ramp angle on the bottom thread will
prevent the stud from turning while the nut is being tightened.  Otherwise
prevailing torque on the last incomplete thread is all that prevents the
stud from turning.  Binding on the incomplete thread is also all that keeps
the stud from unscrewing when the nut is being removed.  This is why
self-locking nuts have a tendency to unscrew the stud when being removed.
That also makes it difficult to back the nut off 1/4 turn if you want to
re-torque it later.

If you back the stud out a little in attempt to synchronize location of a
cross pin hole, chances are pretty good that the stud will rotate again and
end up in a non-predictable final position when tightening the nut.

Barney Gaylord
1958 MGA with an attitude
http://MGAguru.com


At 09:13 PM 1/7/2013 -0600, Glenn Schnittke wrote:
>I've been working on this same question on an XPEG. The response from 
>the old hands I've talked to has always been ' rearrange the nuts to 
>best fit and  then shave the bottom of the rest on  a glass plate to 
>fit'.
>
>My thought on that is 'what keeps the stud itself in place'? There's 
>never a torque value for bottoming the stud into the block. And there's 
>no mechanical device to keep the stud from backing out, so what's 
>keeping the whole assembly from backing out even with the cotter pin 
>through the castellated nut or nylock or whatever you're using on the 
>top side?
>
>It's just one of those things that has puzzled me through the years
>- what keeps a stud from backing out when the nut holding whatever it 
>is in place has a VERY specific torque value?
>
>Moss's answer seems to be nylock nuts. I don't trust them. On top of 
>having to figure the friction value onto the eventual torque value, I'm 
>concerned about how the heat will affect the nylon over time. If I have 
>to go to a locking nut I should rather trust an aircraft nut which has 
>a metal-to-metal contact and I'd still have to factor in the friction 
>to the eventual torque value.
>
>I've seen all kinds of discussion on specific torque values for heads, 
>main caps, conrods, etc. I've found nothing in any manual or discussion 
>about the proper torque for bottoming a stud. I'm sure I'm going to 
>excite all the engineers on the list by bringing this up, but why can't 
>I just back off the stud just a little bit to move the cotter pin hole 
>to meet the castle nut?
>....


>>From: Duvall Video Productions<mike at duvallvideo.com> 
>>To:mgs at autox.team.net
>>Subject: [Mgs] loctite question
>>....
>>
>>Anyone use red loctite instead of mechanical fasteners on main cap nuts?
I
>>have an MPJG engine from a TA when I torque down the mains, the holes
don't
>>line up to the castle nuts for the wire.   I don't want to over torque and
if
>>I back them up to match the hole, I loose my torque.
>>....
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