Gearbox Bearings

Post by **alanworland** » Thu May 21, 2009 11:21 pm

Does anybody know what bearings are used in the sidevalve gearbox?
I feel my box after covering 138000 could benefit with some replacements. Looking in the manual I see that the nose of the mainshaft and the laygear use bushes (bronze?) rather than needle roller assemblies.
I was hoping to obtain the required ballraces and bushes before dismantling

Post by **mike.perry** » Fri May 22, 2009 12:26 am

Your best bet is to take the bearings to your local bearing shop and get them to match them up. I believe John Evans (p.10 Minor Matters) has recently done a Series MM box

Post by **tortron** » Fri May 22, 2009 11:19 pm

Let us know how you get on,
i wouldnt mind having a rebuilt box ready to go (once i get around to rebuilding everything else

)

Post by **alanworland** » Tue May 26, 2009 9:24 pm

I spoke to John Evans today and he says the ball races are readily obtainable (I think he has them about £10/12 each)
John also says layshaft bushes are long lasting - he has never fitted any, but he has a limited stock (£5/6 each)
The bush in the rear of the input shaft (called drive gear in manual) some times require changing, but none are available - John will manufacture if required.
It would appear the main problem area with the box is the 'double top hat bush' that the second gear and third gear run on (item 38 in manual) this has a splined bore which fits the mainshaft and according to John out of the 20 or so MM boxes he has worked on 18 have had this bush broken into three pieces! it can be replaced (manufactuured by him) at I believe considerable expense.
The broken bush it seems will survive if left un-disturbed for a long time and when it does give up, difficulty will be experienced with gear changes.
So, John (and I!) think its a case of - if it aint broke, dont fix it!