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Dismantling gearbox

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Dismantling gearbox

Posted by john_hadow at January 11. 2018

Ive got to the point   where the layshaft is to be removed and Ive noticed that the sleeve gear is sliding up and down 1/2 inch through the shell. The only reason its not sliding further is that its teeth are fouling on the teeth of gear 3 Lay.

Question 1. Am I right in saying that the sleeve gear is sliding on the inner race of the mainshaft bearing or possibly the whole bearing is loose in the casting?  Maybe a spot of loctite would do the trick in either case ?

Question 2. To investigate further I need to remove the layshaft. I have tried heating the back of the shell behind the layshaft bearing (until spit sizzled) but the layshaft would not pull out. Maybe the bearing has been loctited . Any suggestions on how to proceed?

The only thing I can think of is to  remove the gearbox from the frame and attempting again.

Re: Dismantling gearbox

Posted by ian_soady at January 11. 2018

Have you removed the final drive sprocket? The sleeve gear is pulled up tight to the bearing by this. If it's not still fitted the sleeve gear can as you say move longitudinally (sliding in the bearing).

Re removing the layshaft, have you taken the selector rod and selectors out as they can prevent the shaft from moving? The rod has a pair of flats on the outer end which allow you to unscrew it.

Re: Dismantling gearbox

Posted by john_hadow at January 11. 2018

Previously ian_soady wrote:

Have you removed the final drive sprocket? The sleeve gear is pulled up tight to the bearing by this. If it's not still fitted the sleeve gear can as you say move longitudinally (sliding in the bearing).

Re removing the layshaft, have you taken the selector rod and selectors out as they can prevent the shaft from moving? The rod has a pair of flats on the outer end which allow you to unscrew it.

Yes Ive removed both the final drive socket and selector forks and spindle.

(Surely the sleeve gear should be a tight fit on the inner race of the sleeve gear bearing? )

Re: Dismantling gearbox

Posted by ian_soady at January 11. 2018

It can't be too tight a fit otherwise you wouldn't be able to fit it.....

The outer race should be a close fit in the shell so it doesn't turn but the sleeve gear is locked to the inner race via tightening the sprocket nut as I said. It should be a push fit (ie no play but capable of being fitted with just firm hand pressure).

Have you removed the mainshaft?

Re: Dismantling gearbox

Posted by john_hadow at January 11. 2018

Previously ian_soady wrote:

It can't be too tight a fit otherwise you wouldn't be able to fit it.....

The outer race should be a close fit in the shell so it doesn't turn but the sleeve gear is locked to the inner race via tightening the sprocket nut as I said. It should be a push fit (ie no play but capable of being fitted with just firm hand pressure).

Have you removed the mainshaft?

Yes, the mainshaft is removed.  Im beginning to understand. Perhaps I should  start reassembling the gearbox without  removing the bearings. The bearings seem to run smooth without excess play.

The bike  was built in 1970 and supposedly has 41000 on the clock. So not a terrific amount of wear.

Re: Dismantling gearbox

Posted by ian_soady at January 11. 2018

The main weakness in these boxes is the inner layshaft bearing so my preference would be to strip it and check. The shell can also crack between the 2 inner bearing housings.

My first Commando (an ex-Interpol) which I bought in 1981 had suffered the layshaft bearing failure, locking the gearbox up. Which is why I got it cheap.......

Re: Dismantling gearbox

Posted by john_hadow at January 11. 2018

Previously ian_soady wrote:

The main weakness in these boxes is the inner layshaft bearing so my preference would be to strip it and check. The shell can also crack between the 2 inner bearing housings.

My first Commando (an ex-Interpol) which I bought in 1981 had suffered the layshaft bearing failure, locking the gearbox up. Which is why I got it cheap.......

Ok so how should I proceed getting the layshaft out?. As I said I got the bearing housing pretty hot but the layshaft wouldn't budge. If I was to remove the gearbox from the frame how do I adjust the position of the gearbox correctly when it's returned?

 

Re: Dismantling gearbox

Posted by ian_soady at January 11. 2018

You must already have dismantled the primary drive so all you have to do is remove the top & bottom pivot bolts to get the whole box out. It's a long time since I did this but there's a cutout in the engine plates so that you can rotate the box to remove it without taking the engine out as well.

If you leave the primary chain adjuster where it is then that will be a good starting point for getting it all adjusted properly when you refit it.

Given what you've removed already I can't see any reason for the layshaft not to come out unless someone has used bearing fit or similar on it. As a last resort you could drill a 5/16" or so hole in the casing and use that to drift the shaft out but it should not be necessary. The hole can of course later be tapped and a setscrew used to seal it.

I take it you have removed all the gears from the mainshaft and as many as you can from the layshaft? I would expect the layshaft to feel quite floppy at the outer end.

I take it you have the proper Norton workshop manual?

Re: Dismantling gearbox

Posted by christopher_winsby at January 11. 2018

Look up Old Brits Norton Technical articals. I would remove the gearbox and heat in oven and if lucky the bearing will come out with the layshaft. Then you can remove the bearing from the shaft.

Re: Dismantling gearbox

Posted by norman_lorton at Friday 10:10

John, the casing needs to be near 200 degC for the layshaft bearings to come out, and that sort of temperature is not easy to reach with the case in the frame. A hot air gun in a clamp and pointed at the back of the case for a good 10 minutes or more. A IR temperature readout does help see what is going on.

Better to take the case out completely, then you can be sure that you can heat it and and bits go back in properly while on the bench.

Get a new roller layshaft bearing from Andover rather than a ball bearing from someone else.

Re: Dismantling gearbox

Posted by john_hadow at Friday 17:45

Thanks all for your help, I've decided to go ahead and take the gearbox out of the frame and  pop it   in the oven.  I'll  let you know how it goes !

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