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

[Charley & Peggy Robinson]

Now, that's darned interesting!  I have always wondered why some head 
studs were coarse thread on the end into the casting  and fine thread 
for the nut.  Just never bothered to look it up.

Thanks for the post,

CR
On 1/8/2013 8:40 AM, Barney Gaylord wrote:
> 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.
>>> ....
> _______________________________________________
>
> Mgs at autox.team.net
> Donate: http://www.team.net/donate.html
> Suggested annual donation  $12.75
> Archive: http://www.team.net/archive
> Forums: http://www.team.net/forums
> Unsubscribe: http://autox.team.net/mailman/options/mgs/ccrobins@ktc.com