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@duvallvideo.com>
>>To:mgs@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.
>>....
_______________________________________________
Mgs@autox.team.net
Archive: http://www.team.net/archive
Unsubscribe: http://autox.team.net/mailman/options/mgs/mharc@autox.team.net
|