Losing gearbox pivot stud .

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Richard Tool

Richard Tool

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Let me run this by the readership at large and have better minds than mine weigh in on this ...
Took the Commando for a short ride two weeks ago . When I went to restart at my destination to return home the kickstart felt ” different “.
When I returned home I was cleaning the road grime off the underside when I discovered the gearbox pivot stud was completely missing .
Initially I blamed my self for not tightening the nuts fully and not checking on them . I ordered a new one with nuts from RGM and put the bike on the lift to service it while I waited . When the new stud arrived I went to install it and discovered that it can only be inserted from the timing side because of the primary drive case and at that the right exhaust had to be undone at the silencer mounts in order to deflect the header pipe enough to allow the stud to enter squarely. Job done with some effort to get the holes lined up I wondered how could the entire stud have come out on its own if the exhaust system had to be moved in order to allow the stud to pass.
Chalked it up to all the dynamics involved in a running motorcycle and moved on to re torquing the barrels and head , valve lash etc. and so removed the fuel tank . That is when I discovered the Dave Taylor type head steady had come adrift from the frame because the screws to the frame clamp went missing. In hindsight I recall not using thread sealant on them during the build because I expected to be having to adjust it - my bad .
Now I am wondering ( here’s the part I need opinions on ) if the side to side deflection of the engine/ gearbox / cradle because of no head steady could have imposed a shear load on the pivot stud in some way in order to break it in two and thus have two shorter pieces that could consequently now exit in the space available.
Anyone think this is a sound theory or am I overthinking ?
 
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I can't see how the gearbox pivot bolt could have come out with the exhaust in the way!
By the same token I cannot see how the side to side movement of the engine in the frame could really affect the the gearbox bolt
The engine is bolted to the gearbox cradle
The cradle itself would be under some strain, but the majority of strain would be taken up by the front and rear ISO bolts
 
The gearbox pivot is a stud with nuts at each end. Why couldn't it come out if a nut fell off?
 
i wouldn't put anything past a Norton vibration... they are untamed monsters... and will get the job done... 10min without loctite and the GB adjustement bolt was gone. sothe pivot bolt requires abit more finess and the Norton vibration monster will rise to the ocassion.. no problem!@#$%^&*
 
maylar said:
The gearbox pivot is a stud with nuts at each end. Why couldn't it come out if a nut fell off?
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Because the distance between the cradle and the inside of the right exhaust is less than the the overall length of the stud - the distance between the cradle and the inside of the inner primary even less .
That being said , it seems to have found a way !
 
It's very odd
I have had the top bolt become slack on a couple of occasions but because I have a belt drive I also have 2 gearbox adjusters
This has held the gearbox in place , but the bottom pivot stud remained tight
 
Very odd indeed. On my '64 Atlas, which uses the same setup, it is impossible to remove or install this bottom bolt (stud) without major surgery. I ended up removing the forward engine plate and the four bolts that hold the plate to the frame aft of the gearbox.
I could then slide the whole works forward and pivot the gearbox upwards to enable the necessary clearance to slide the bolt past the bottom frame tubes.
Of course, any thru bolts would have to be removed before trying this. It brought to mind the English version of the wooden interlocking puzzles so common Asia.
 
I've not used loctite on any of those transmission bolts. Nor any of the engine/carrier mounting bolts. No issues.
Also, I noticed a friend's trans pivot bolt missing a nut while at a gas stop. it is captured as mentioned above.
 
I have just been through the same issue, in my case definitely my bad for not fully tightening the bottom stud after replacing a primary chain.
Loaned the bike to a gent who reported a loose gear lever when we got back, but it was the bottom stud which had disappeared.
DT headsteady here too but that is still firmly in place so the engine wasn't swaying around.
Had the same stud install issue, the only way to get the replacement in was to remove the exhaust.
 
I don’t use loctite on eng / trans / cradle fixings either. Moreover I don’t use loctite on any fasteners that require regular checking and tightening.

Its worth remembering that a fasteners job is to apply clamping force to the surfaces it is holding together. When we check for tightness, we’re checking this clamping force.

Loctite doesn’t ensure fasteners are or stay tight. All loctite does is ensure the nut is glued to the bolt! It might feel ‘tight’ but you have zero feel for the clamping force.

The danger here is that when things ‘settle’ the glued nut tricks you into feeling tight when it is not, then the problems begin.
 
Fast Eddie said:
I don’t use loctite on eng / trans / cradle fixings either. Moreover I don’t use loctite on any fasteners that require regular checking and tightening.

Its worth remembering that a fasteners job is to apply clamping force to the surfaces it is holding together. When we check for tightness, we’re checking this clamping force.

Loctite doesn’t ensure fasteners are or stay tight. All loctite does is ensure the nut is glued to the bolt! It might feel ‘tight’ but you have zero feel for the clamping force.

The danger here is that when things ‘settle’ the glued nut tricks you into feeling tight when it is not, then the problems begin.
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I agree that any fasteners that may require regular checking shouldn't have Loctite or any other thread lock applied ... But I don't see what the difference is between Loctite, Nylon type nut, Distorted thread lock, philidas nuts etc.. If for what ever reason the clamping force is lost...stretch bolt/stud, poor component assembly, surface cleanliness etc. then the nut fixing will remain tight at that place on the bolt/stud.
Surely The only type of fixing that apply a positive load (to a small degree) is a spring washer, shake proof washer or Belleville washer??
 
Hmmmm.... I have a complete top stud & fittings arrangement in the "For Sale" section, cheap...
 
olympus said:
I agree that any fasteners that may require regular checking shouldn't have Loctite or any other thread lock applied ... But I don't see what the difference is between Loctite, Nylon type nut, Distorted thread lock, philidas nuts etc.. If for what ever reason the clamping force is lost...stretch bolt/stud, poor component assembly, surface cleanliness etc. then the nut fixing will remain tight at that place on the bolt/stud.
Surely The only type of fixing that apply a positive load (to a small degree) is a spring washer, shake proof washer or Belleville washer??
Click to expand...
“Breakaway torque” is far different for Nylock & Loctite.
 
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Somewhat irrelevant, but on the P11 that stud and two nuts arrangement for the gearbox pivot can walk right out the timing side under the foot peg mount unobstructed. I'm also darn sure the P11 vibrates more than a Commando. Everything is solid mounted.

I use star washers behind all the big nuts holding the engine and transmission in the frame. Not an elegant solution , but I haven't lost any nuts or bolts.

Yes no head steady would probably loosen things up enough for that entire stud (once the drive side nut came off) to find a way over or under the exhaust pipe and on it's way to freedom. Just an opinion, since I haven't had a Commando since around 1984 and don't know what all that looks like down there. I know the motor with those two big slugs pumping up and down would be moving a lot without a head steady.
 
Schwany said:
I use star washers behind all the big nuts holding the engine and transmission in the frame. Not an elegant solution , but I haven't lost any nuts or bolts.
Click to expand...
Nordlocks, if there's enough thread
 
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