Rebuilding my Navigator gearbox, which very occasionally jumped out of first.
I have 2mm of free travel on the kick start, and therefore also the first gear on the layshaft when assembled just with the layshaft, and kickstart shaft as per attached pics.
I've tried P26 of the lightweight twins compendium but the numbers are not clear to read, (point 43 on the exploded diagram)
There is a hardened washer behind the kickstart shaft. 2mm seems a lot to take up with shims, I do have a bit of phosphor bronze and a Myford, but is something else missing here?
Thanks
Further pics
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Jumping out of first
Hi David,
Sadly, jumping out of first is not uncommon on Jubilee & Navigator models after all this time.
Over the years, there is wear on the the thrust faces of the two bushes at either end of the layshaft, both in use & when kickstarting. Engagement of the ratchet teeth relies on a pushing motion!
The 2mm of play you detect is enough to let the kickstarter 1st gear (48) float that little bit more than it should, I suspect if you took it off the shaft and looked on its back, you would see witness marks where the dogs from the adjacent selector gear (47) slipped out & back in. The numbers in brackets are the numbers of the gears in the 1961/62 Parts List Booklet.
I have used your photo to show you where to place a shim to take up the 2mm of slack. You should shim it such that that you can't detect any end float - but the kickstart is free (and the back wheel spins freely in neutral).
While you have the gearbox apart, there is one other item you must check. Failure to check this could be disatrous. The layshaft spins in a bush at the far end. Sadly, this bush is not pegged to prevent rotation. If/when it moves, it blocks the oilway and compounds the problem. Once the bush 'picks up', it can damage the crankcase very quickly, as brass is tougher than ally.
I advise removal of the layshaft and check the condition of the bush. Quite often it comes out on the end of the layshaft, of if you insert your pinky into it. If you deem it is in good condition and have the facility, I would strongly suggest (if you were able to remove it) you Loctite it with Bearing Retainer, ensuring the oilway is lined up & then, if you can, pegit in place. If you are convinced all is well with the bush, then peg it in place to future proof yourself.
Attached is (1) your picture, showing where to shim, and (2) showing the layshaft bush pegged in place an later bikes. You should try to do the same to protect your bike - but its not an easy task!
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1st gear shim
Hi David,
The shim can be a plain steel washer just under 2.0 mm thick. You may have to adjust the ID and OD in the Myford. It doesn't take any thrust loads.
Peter
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The kickstart shaft