Forum

[JTL]

Hi all... as part of a 35000 km gearbox overhaul I'm replacing both the layshaft and the bushes for the layshaft (new ones: our hosts phosphor bronze counterparts). The bush for the kickstart spindle is already replaced, and now the layshaft doesn't fit. Bush inner diameter is 18,15 mm; new layshft kickstart spindle end is 18,25 mm. What should the optimal tolerance be? And how do I fix it? Shaving off some material from the bush or the layshaft? And how to do it? I'm planning to do the case end bush next week. Anything in particular I should be observant about... After Bullet Whisperer mentioned a gearbox lockup at 100 mph because of a too tight bush/layshaft combination I'm pretty determined on getting this right. So, advice is much appriciated... regards Jacob

[PeteF]

I would teams the bush with an adjustable reamer untill you achieve an easy sliding fit.

[PeteF]

Damn spell checker, ream the bush.

[JTL]

Hi Pete... thanks for reply. The reamer thing was my initial thought, but where to get such a tool. I have never seen them before this small here in Denmark. Well, the internet might come in handy once again for this search. What about tolerance? Is it just a question about feeling an easy sliding fit or does it have a value in mm's?

[Tim NZ]

The bushes are finished machined to be the correct fit once it has been pressed into the Kickstart.


I have never encountered a tight one, more often and more likely to be too loose as a result of wear to the layshaft itself. In which event the new bush does not last long.
I usually replace the lay shaft at the same time and occasionally get the old shaft refurbished. Metal sprayed and reground, but new ones are cheaper...

[JTL]

Hi Tim... as written in my intro to the problem both bush and layshaft are new. The layshaft is a RE factory part and the bush is our hosts part # H15. Before fitting the bush to the kickstart spindle it had a tight fit to the layshaft and now it doesn't fit. The bush for the case end has a nice fit before fitting. I plan to replace the case end this weekend. After this I know if it still has a nice fit. I have tried to upload pictures, but don't know if it works... Jacob

[JTL]

Well, the pix upload was no success, but they are pictures of the new and old layshaft (kickstarter end) and the new bush in the kickstarter spindle. I happen to have another kickstarter spindle with a new oem bush lying around. The new layshaft has a nice fit in this one. I guess some careful reaming can do the job.

[papasmurf]

[JTL]

Papasmurf, thank you for helping me out on making the pictures visible. I hope the one on the old layshaft shows why I had to do something about new bushes.

[Adrian]

The trick for the pictures is to copy and paste the HTML code and NOT the image code, which is what most forums use, but not this one...



I think your 18.25mm is actually 23/32" of an inch, and if the blades of an H7 parallel expanding reamer (21/32"-23/32" range) won't reach far enough into the blind hole you will need a plain reamer with cutting flutes going right to one end. I had a quick internet search last night, and while there seem to be no hand reamers the correct size which you can use with a normal tap wrench, they are available on ebay UK as machine reamers with a morse taper fitting for use with drill presses and lathes, so a machine shop could help you out if you get one - unless you already have a morse taper to tap wrench adapter lying around!



A.