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Twin gearbox problems

Jock English

Forum Website User
Non-VOC Member
My 1951 Rapide recently lost all gears except third and I have found a very badly siezed and wrecked selector. When I reassembled the box I fitted the 31 thou shim on the end of the clutch shaft which was missing when I stripped the box.
I now find that that the clutch shaft is very tight and I cannot get neutral, or perhaps I select it and the clutch shaft is locked up by end load. However there appears to be no neutral when I test the box, as the clutch shaft still rotates when I spin the back wheel.
When I have loosened off the large cover plate I can get neutral OK, so I suspect that the shim had been left out previously for that reason.
I have had the bike for about three years but never ventured into the gearbox before, never needed to!
Is it safe to leave this shim out?
Any help would be appreciated, Cheers
Jock English
 

Bill Thomas

Well Known and Active Forum Website User
VOC Member
Hello Jock, This is a shot in the dark, I think we had something like this a few weeks ago and the bloke found he put the layshaft in the wrong way round, If you put the gears on the lay shaft in your hand and then swap the end gears end to end, you will see the gears fit flush with the end of the splines only one way,( the right way ). If they are wrong when you tighten the cover plate it locks the lay shaft. That shim I think should be put in, the fact that you could not find it might be because they get ground up if the clutch nut is not tight, Hope this helps, good luck,Bill. P.S. Try putting the cover on with out the layshaft and it's gears, to test the end float with the shim in on the main shaft.
 

clevtrev

Well Known and Active Forum Website User
VOC Member
Hello Jock, This is a shot in the dark, I think we had something like this a few weeks ago and the bloke found he put the layshaft in the wrong way round, If you put the gears on the lay shaft in your hand and then swap the end gears end to end, you will see the gears fit flush with the end of the splines only one way,( the right way ). If they are wrong when you tighten the cover plate it locks the lay shaft. That shim I think should be put in, the fact that you could not find it might be because they get ground up if the clutch nut is not tight, Hope this helps, good luck,Bill. P.S. Try putting the cover on with out the layshaft and it's gears, to test the end float with the shim in on the main shaft.
Probably the reason for the missing shim, is given by the fact you are binding between the mainshaft and the output shaft.
So it was left out for this reason. It`s the only reason it`s there, to give some leeway to get the right clearance between output shaft and mainshaft.
 

Jock English

Forum Website User
Non-VOC Member
Thanks for your reply Bill, I thought about the layshaft after reading about it in "40 years on", and took the box down again and found it was OK, still worth the effort, at least I know it's right.
With the shim in the cluth shaft is tight enough to transmit drive in neutral, I worry that I may have trouble getting neutral if I leave it there, would it be better with a bit more end play, rather than too little?
regards
Jock

Hello Jock, This is a shot in the dark, I think we had something like this a few weeks ago and the bloke found he put the layshaft in the wrong way round, If you put the gears on the lay shaft in your hand and then swap the end gears end to end, you will see the gears fit flush with the end of the splines only one way,( the right way ). If they are wrong when you tighten the cover plate it locks the lay shaft. That shim I think should be put in, the fact that you could not find it might be because they get ground up if the clutch nut is not tight, Hope this helps, good luck,Bill. P.S. Try putting the cover on with out the layshaft and it's gears, to test the end float with the shim in on the main shaft.
 

Jock English

Forum Website User
Non-VOC Member
Thanks Trev, as it did select gears OK without the shim, I may well rebuild it without, depending on any other replys.
I feel that a bit too much play is preferable to a tightness between the clutch and output shafts, which I have with the shim in place.
Why do they break down when the sun is shining?
Regards
Jock
 

stumpy lord

Well Known and Active Forum Website User
VOC Member
hi,
dont forget that the shim E76 comes in varius thickneses, o.oo5 and 0.o10. It could be that on your engine a 0.031 shim is to thick.
perhaps worth trying with a thiner shim.
regards stumpy lord.
 

clevtrev

Well Known and Active Forum Website User
VOC Member
Thanks Trev, as it did select gears OK without the shim, I may well rebuild it without, depending on any other replys.
I feel that a bit too much play is preferable to a tightness between the clutch and output shafts, which I have with the shim in place.
Why do they break down when the sun is shining?
Regards
Jock

There`s no play in either the ouput or the mainshaft, each are pulled up to their respective ends. Before you tighen up the clutch end try to push back the shaft, and that will tell you how much clearance there is between the two. 5-10 thou is fine. As it will get bigger as the engine gets hot.
Why do they break down when the sun is shining ? That`s because that`s the time you go riding........
 

Bill Thomas

Well Known and Active Forum Website User
VOC Member
Hello Jock, As Trev says the clutch nut holds the shim tight one way and the final drive shaft nut holds that the other way, I wonder if there is a problem the other end ? I have always found that if the shim is worn away G6 is not far enough in mesh with G11 and will round the teeth off, In time.Those bushes in G4 do some funny things sometimes may be worth looking at. Sorry can't be more help, it sounds like a strange one, Cheers Bill.
 

Jock English

Forum Website User
Non-VOC Member
Thanks again, I have now checked and with no shim there is only .022" end play, so it's not surprising that it tightens up with a 31thou shim.
I have just been to Kettering (I live 20 mins away), and bought a selestion of shims which will allow me to set it up with a few thou when cold.
I hope that will work.
Many thanks to everyone who has responded, what a wounderful source of knowledge and help you all are!
Cheers
Jock

Hello Jock, As Trev says the clutch nut holds the shim tight one way and the final drive shaft nut holds that the other way, I wonder if there is a problem the other end ? I have always found that if the shim is worn away G6 is not far enough in mesh with G11 and will round the teeth off, In time.Those bushes in G4 do some funny things sometimes may be worth looking at. Sorry can't be more help, it sounds like a strange one, Cheers Bill.
 
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