Ariel Owners Motorcycle Club

I've had the box apart three times now, new bushings new gears, new shift fork. I have no gasket on the cover plate - just yamabond at this point with no leaks -- and the shift lever is moved out a bit from being flush with the gearbox cover I did have 00 grease in the gearbox but I'm running straight 50 weight now. It seems "a little" better -- but when I accelerate hard it jerks and will pop out of gear in second only. The rest of the gears are fine and it runs beautifully well past 75mph.

What am I missing here?

Reading your older posts, I can see you have had some fun with that box!

A few questions:

When you replaced the gears, did you examine the shafts for endfloat? Did you look at the sleeve gear endfloat? Did you replace the sleeve gear bushes?

I'm thinking about the possibility that the shafts (or the sleeve gear) are moving enough to disengage the dogs on the mainshaft/layshaft second gears, or perhaps that the sleeve gear bushes are not fully home & are preventing the adjacent gear from engaging it's dogs fully. I've recently put a 0.75mm shim on a Burman sleeve gear to prevent it sliding about to it's heart's content...

That's the thing. I need a diagram on where to put the shim and what size to get. I keep hearing shim, and I have zero idea about where it goes!!!

Probably worth checking, although you might have done so already. There are two pins that engage with the selector drum, are they worn at all?
(A very long shot might be the drum itself worn, but I've never come across that, only worn pins).

SG

Pins are new from our friend industry hereford.

The usual cause is worn engagement dogs on the gears, also it can be too long a shoulder on the bushes, preventing the gear moving the full distance, worn selector forks or a combination of any or all of these. The dogs do not engage by very much so it only takes something to be slightly out for this problem to occur and sometimes the easiest thing to do is to add shims. How thick and where is difficult to say but somewhere that they will mean that the dogs mesh more deeply. There are places where you shouldn't put shims, preferably not next to rotating splines that could chew it up. Mainshaft end float should be minimal, 1/64 is the figure given. Check also for end float on the layshaft, here you can fit shims under the top hat bushes, renew the bushes or make up one with a thicker top hat rim. Is the positive stop button (3707-52) and spring in good condition?

Gears and selector forks have less than 30 miles on them bushes are new, stop button and spring are new. Taking out the gasket on the cover improved it a little. So did leaving 1/8" gap at the shift lever between it and the case. It doesn't jump out so much...

dgurovich wrote: Tue Sep 15, 2026 7:01 pm Gears and selector forks have less than 30 miles on them bushes are new, stop button and spring are new. Taking out the gasket on the cover improved it a little. So did leaving 1/8" gap at the shift lever between it and the case. It doesn't jump out so much...

If you can get at the gearbox sprocket, see how much it moves in and out. Sleeve gear end float affects engagement of the dogs on the next gear...