Hi all,and a belated Happy New Year,
I'm well on my way to sorting out an oil leak and broken kick start return spring on my wm20 gearbox,with the box out and jigged on the bench and being striped down(Whilst getting the gearbox out found that the cush drive spring was broken ,didn't expect to find that).I've got the service sheets to work from but i was wondering if there were anything to watch out for or any top tips that aren't in the books,as i've never touch this job before.Most parts are to be found at Russells motors,but i'm not sure of the part number for the oil seal at the sprocket end?
As i've got my typing head on,does anyone know what these carbs fitted and if they would be any good on My M20:-
276/014R (1 inch)with a IAU(7 degree angle)float
276/024R/ (1 1/16th inch)(170 jet)with a 1B float M21?
276/410R (1 inch)
Any advice will be gratefully recieved,
cheers ,Phil

Hi Phil...If it is a military M20 with the correct box there is no oil seal fitted at the sprocket end. If you have a later box, with the seal, the part number is 65-3508.
It would require a very large posting to cover the gearbox in detail and there are numerous items that need to be checked and set up correctly during refurbishment.
Factory worksheets give a good guide to the basics but as far as I know there is nothing in print that details everything that is relevant.
Key items are..
Correct shimming of the shafts within the gearbox case (end float)
Sleeve gear bushes in good condition and within tolerance.
Mainshaft unworn where it contacts sleeve gear bushes (shaft and splines)
Selector forks, tracks ,pins and dogs in good condition without excessive wear.
Indexing plunger and spring and self centering plunger and spring in good condition.
Location in ratchet plate for self centering plunger in good condition.
Ratchet teeth and pawls and gearchange return springs in good condition.
Layshaft bushes in good condition.
Layshaft selector dog set correctly on assembly.
Kickstart ratchet assembly set correctly on assembly.
I would suggest you examine all the components with the list above in mind and then post about each thing you are unsure of..Ian

email (option): julie@wright52.plus.com

Hi Ian ,
Thanks for the help.The box is the early military one 1938-48 for a 1943 WM20.With no oil seal,that asks the question how and where is the oil getting out and how to stop it?I did find part no.24-4232 sprocket oil seal for a 1938-1948 M group box.Everything was working fine when i started(apart from the leak and kick spring),so unless there is something obviously worn/broken,i hope to not have to replace to much,but your list is a great pointer.Being a carpenter with no training as a mechanic i get a bit lost if it gets to technical,so please keep it simple,i promise i have some spanners etc and not working with my hammer and chisels.
cheers again,Phil.

The big bearing on the drive side of the box is a metric bearing that is easily available from bearing suppliers, you can fix the leak by purchasing one with a rubber seal on one side, or get one with 2 rubber seals and simply pop one out of it, then simply place the bearing in the case with the rubber seal on the out side of the box

email (option): davmax@ntlworld.com

Hi Phil, the best solution to gearbox leaks is to have the sleeve gear bushes/mainshaft in good condition and to replace the gearbox main bearing with a sealed type. These have rubber seals fitted as standard.
You can obtain one easily from any bearing stockist...part no. 6207 2RS.
The '2RS' stands for 2 rubber seals. I remove the seal from the side nearest the gears before fitting to allow gearbox oil to lubricate the bearing...but I believe some don't do that. The seal can be prised out quite easily with a small screw driver or similar...Ian

email (option): julie@wright52.plus.com

Or what Dave said while I was typing my post ..Ian

email (option): julie@wright52.plus.com

Thats just the help and advice i was hoping for that i can understand,cheers.
I shall continue stripping down the box tomorrow ,wonder what i'll find?

I found that the Kick start spring did not fit in the ratchet as neatly as I would have liked. Due to the cast land in the gear that the spring hooked into has square edges and the spring is rounded. So I filed a radius in the gear for the spring to hook onto. less chance of damaging the spring I thought.
Regards
Michael

email (option): michael@nammech.aom.au

Did you have a look at the technical info section of the website? Lots of tips about the gearbox!

email (option): viaconsu # planet dot nl

Hi all,
Thanks Micheal,i'll look out for the fitting of the spring onto the kick starter.Well reminded Hans on the tech pages,I've printed them of so that they're infront of me when working on the box,with the work sheets.I've got to get on with the box and refit it as i have to MOT it soon,so off down the shop,i'll let you know if i succeed or i'll be asking again for help
cheers Phil

phil there is nothing in an MOT that says you have to have a gearbox i was have one of my classic bikes MOT ed there was a chap in front of me have his classic bike pass the MOT he trailered it there as it didnt run

email (option): roger.back@node6.com

Hi,
The gearbox is out,in bits and on the bench.I've gone through the parts of the box and everything seems ok i.e wear etc of Ian's check list.The one thing i'm not sure of is the bearing (sprocket end)appears not to be tight up to box casing as the thin washer between bearing/case seems loose.Does the bearing need seating to the case/tighter,as this may be why there is an oil leak?I'm going to get the parts ordered in the next day or two,so i can get on with putting it all back together before i forget how goes(i did take loads of photo's for ref).
If i don't get it back together before the MOT is due and i had a trailer,i might give it ago with no box in it,as you say Roger.I guess if the lights, brakes,bearings and horn work ok maybe you don't need a functioning bike with gearbox.Some MOTers can be a bit picky,as one made me tape up my lights as i did not have a dip switch fitted.Could you try it with a car?
That's the update so far so good,I shall let you know how it goes,thanks for all your input to date,
Phil.

Hi Phil, the shim fits into a slight recess in the gearbox case so is free to 'float' even with the bearing fully in...Ian

email (option): julie@wright52.plus.com

Thanks Ian,That answers that one.I intend to replace the bearing with the one you recommended,as it is a bit worn.
Cheers for now,Phil.

My own MOT guy who is very friendly and quite lenient. Always insists that the bike must run, so he can check the exhaust for sound and leakage. Ron

email (option): ronpier@talk21.com