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gearbox rebuild

Hi all..I am rebuilding an M series gearbox. The problem I am having is that there is a slight tight spot in it when the main shaft is rotated. It selects gears ok. I added more gaskets which did loosen it up but still a tight spot and now too much play in the selector arm. The Main and layshafts look straight. I am thinking perhaps re-bushing everything, might fit the issue but the bushes look ok to me. As well does anyone know where I can get hold of some new gear selector dogs as the ones in the box are worn.

Re: gearbox rebuild

Hello Bryce,

I have just finished rebuilding an M20 gearbox from most NOS part,
Including the shafts and a NOS dogs.

I found NOS dogs on eBay. they do come up from time to time.
My gearbox also came out a bit tight, mostly in one spot, (But I could turn it over manually)
And I thought I might have bent it, as I used some real force and heat to fit few of the new gears to the shaft.

I have also asked here, and the reply was that tight gears boxes eventually seizes,
But as I had no choice, I topped it with oil and installed it.
It shifts fine and all looks great.

So far I have done over 250Km on it and all is fine.
My logic is that the more it is used, the less is the probability for seizing,
So I hope it will do fine,
But basically the gearbox should be very free to turn.

Hope it helps...


Re: gearbox rebuild

Thay's interesting, Noam.
Wonder if the box will hold after many more miles.
Let us know how you get on, oke ?

And Bryce, are you sure you have all the many rings and shims inside and on the right place ? It's very important to get the box working properly.

I must say i have rebuild gearboxes of triumph, Norton, Ariel etc, but never had any problem. BSA's need much more care and attention...

Re: gearbox rebuild

Hi Bryce, If you place one shaft at the time you can figure out if its the main- or layshaft.

You can also find tight spots when the sleeve gear is not properly rebushed.

Good luck! Michiel

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