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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 January 12. 2018

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 January 12. 2018

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 !

Re: Dismantling gearbox

Posted by john_hadow at January 22. 2018

I heated the shell in an oven to 200 C. The sleeve bearing fell out  and the layshaft bearing came out after a hard whack onto some wood. Luckily no signs of cracks in the shell. I put the new bearings in the freezer and heated the shell again..The new sleeve bearing dropped in easily with a clunk and I assumed  it would be the same with the roller bearing. I tried pushing it in with a 1 and 1/8 AF socket but it jammed and wouldn't come out so I had to drive it home with socket and club hammer. In retrospect I should have got a special drift made  up

When cool and oiled up the roller bearing showed a tiny amount of resistance when revolved so I guess the housing has shrunk the bearing by a thou or 2??

Not good news so my plan now is to remove the bearings again and use some 800 grit? emery to clean up the housing.

My question is  how hot do I dare get the shell up to, before I whack it down on to some oak wood. Is 250 C or more safe? What's the maximum anyone has got away with ?

What temp does the aluminium start to be affected?

Re: Dismantling gearbox

Posted by norman_lorton at January 22. 2018

That sounds like bad news John. We are all with you and feel the grief!!

Once the bearing goes out of true in a hot case it easily sticks, and the extra problem with a roller layshaft outer sleeve it that it stays there when the shaft and roller set are pulled out!

I think you are right saying that if you had the right size of mandrel, and a nice big bench press, then you could have pressed it all true. Perhaps the problem now is that thumping it has knocked it a fraction of a thou out of true and you can feel that on the roller set when rotating. Getting it hot and pressing it again will not fix that. Also, there might be some swarf scraped off behind the bearing outer.

The aluminium could be heated to 400 degC without harm, but that bearing outer is not going to come out without some push from behind. I think you are going to have to drill two, or better three, 2.5 mm holes in the casing behind the bearing (use a jig and flat bottom the holes with a milling cutter) and make a press tool with three pins set from the same jig. Then when it's all hot (oven at 250 degC) you need a nice 1 or 2 ton press. Three pins will make it a stable push.

Clean out the seating and make it an EASY push fit for the sleeve. Assemble partially and check that all is nice and free and you have the correct few thou of end float when the kick start housing bush is fitted with the outer cover. If the bearing outer is buggered then you can get a new bearing. If all is good then you can disassemble, clean, and fix the bearing outer with permanent, sleeve loctite. Hopefully, if you drilled them accurately, the holes will be obscured by the bearing and the loctite will seal them. You could also plug the holes from the outside with JB Weld or similar.

I have not done the above, but I did fit a roller layshaft bearing a couple of months ago and it is what I would do if I was in your pickle. I do have a workshop so the tooling to make would have come simply. If you have not got a press and can't make the tooling then give the job to a small engineering firm.

best wishes, norm.

Re: Dismantling gearbox

Posted by david_evans at January 22. 2018

Sound like your effort with club hammer have pushed the bearing home on the piss as they say. In which case it needs to come out and be refitted straight. More heat required and try and clamp the main shaft bearing in with a bolt and large disc or washer to avoid disturbing that again. the lay shaft bearing should just drop in all the way to the bottom of the hole. There is a deep groove ball bearing available for the layshaft that eliminates the need to shim the layshaft end float. (sometimes required with a roller bearing)

Re: Dismantling gearbox

Posted by john_hadow at January 26. 2018

Try and imagine the following.

I fixed a slab of 1 and 1/2 inch oak to the face of the shell. Then heated  the shell up to 250 C. Then suspended  the whole thing in mid air with multi strand wire suspended from ceiling and from the floor. I gave my son a club hammer and   he whacked the wood from below as hard as he could.

Good news !

I wasnt expecting the layshaft bearing to fall out so easily but it did and shot out of the  mainshaft housing having ricoched off the wood !

I cleaned up the swarfe in the housing with 240 grit and  now the bearings are finally home and dry. The gears are all in place and working ok so now im going to shim the kickstarter spindle.

Re: Dismantling gearbox

Posted by robert_tuck at January 27. 2018

You will have to open out the shim bore and I would not attempt to closely shim the shaft , I would measure the float then take some out leaving a minimum of 10 thou. Don't be surprised if all your calcs come to nothing and you have to leave the shims out after all to get things to work. Hemmings says don't shim the box!.

Re: Dismantling gearbox

Posted by john_holmes at January 27. 2018

Hemmings used a ball bearing with a special cage so no need for shimming, if you use the roller you need to shim to keep full dog engagement in first gear.

Re: Dismantling gearbox

Posted by robert_tuck at January 27. 2018

I agree with you John, but still had to leave out most of my carefully calculated (dial gauge used) shims before the box worked nicely!. Perhaps the gaskets compressed with time and use?.Logic would seem to say that as the play is developed at the drive side with the introduction of the roller then shimming should be at the drive side. shims at the cover side can only move the parts to somewhere they have never been.Perhaps we shim the coverside purely because ISO shims are easy to get?,if RGM supplied some 5,10,and20 thou shims to go between roller and fixed gear, a better solution? or maybe Hemmings route is best,no shims needed.

Re: Dismantling gearbox

Posted by norman_lorton at January 27. 2018

Well done John! impressive employment of kinetic energy and a fit youngster.

When I fitted the Andover Norton roller it required no shimming. I would guess that the roller bearing is designed to take exactly the same space as the ball bearing?

Re: Dismantling gearbox

Posted by robert_tuck at January 27. 2018

The roller I fitted many years ago left me with about 60 thou end float , And I shimmed the layshaft from both ends as I thought it likely that there was some wear on the KS bush shoulder.

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