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Crankcases assembled but can't select gears

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McCabe-Thiele (Ted):
Don't rush into splitting the crankcase take your time & try suggestion on here. I was going to  taking my cam cover off as I was sure I had made a mistake when setting the valve timing - as it turned out and thanks to advice here I could check valve timing it was okay. Weeks later I found a photo on my project site showing all was OK.

philward:



--- Quote from: philward on May 26, 2022, 08:55:31 PM ---To isolate the problem - ie, whether its the selector mechanism or the internal drum/forks/gears is the problem area, can you not remove the external selector mechanism and try to turn the drum/plates/pins assembly with a large adjustable pair of plyers (with suitable cloth protection on the drum selector mechanism plates) - you may need to turn the output shaft to help gear selection (mimiking the gearbox moving). If this works, you will know its the assembly of the external mechanism.
It may save you needlessly splitting the cases.

--- End quote ---



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Oddjob:
The drum is in the wrong position, it’s almost certainly got one of the dowel pins locating the forks stuck down a slot in the drum instead of inside the track where it supposed to run. As you can’t see or get to these pins without splitting the cases you’re going to have to do that.

Learn the lesson, always check for gear selection before you seal the cases. You made a mistake but luckily you spotted it before you put the engine back in the frame, it could have been a bitter lesson to learn but it wasn’t that bad in the end.

ebmbiker:
Good afternoon guys, found the problem. The 4th gear on the layshaft was on the wrong way round!

Because the engine was disassembled when I bought it, I just put the layshaft assembly in as I found it in the box. At some point in the past, the previous owner must have taken off the 4th gear and put it back on the wrong way. Anyway, I can now put the crankcase halves back together.

This leads me on to another question. Do you apply gasket sealant to the big end-bearing joint faces? The ones that house 2, 3 and 4 main bearings? I didn't the first time I assembled it but was thinking it might need it?

Cheers,

JB

MrDavo:

--- Quote ---Do you apply gasket sealant to the big end-bearing joint faces? The ones that house 2, 3 and 4 main bearings?
--- End quote ---

No they should be dry and clean, that's all. My CB750 crank was completely ruined by a previous owner painting the cases all over, including behind the shells. The tolerances are very fine, after painting they were zero or less, ruining the crank and shells.

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