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1942 BSA M20

Can anyone e mail me a picture of lever positions for starting this bike cold and I am also looking for the best way to stop oil from leaking main gain seal that are cork! I live in USA nw Chicago area looking for other old bike riders!

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Re: 1942 BSA M20

Magneto wire at full retard
If you have a choke, choke closed.
Rotate the engine using the valve lifter till it has just past TDC on compression stroke ( you can hear the air being sucked through the cab )
Return the kickstart to the top then depress t firmly all the way till it hits the stop .
This is just a little further forward than vertical.
Hold it there for a second or two till the engine either starts or stops rotating.
This prevents kickbacks.

The tin chaincase leaks like a seive.
It did so from new and they do not get any better after their 70th birthday ( much like people ).

Start by knocking all of the bolt holes flat.
usually they will be dimpled in from being over tightened.
Get a new soft 1/4" thick gasket.
On mine I fitted washers behind every bolt.
These need to have an edge ground off them to clear the curves in the chain case.
Next is the foot peg holes.
These get worn oval and deformed over time
The solution is to weld a washer inside the holes to make them round again.
Same story with the spacer inside the chain case ( which is often missing ).
I weld some thick washers to either end.
Originally there were cork gaskets either side of this but I found O rings work a lot better.
Finally there is the sliding plate behind the clutch.
That has a large felt ring and these need to be replaced at regular intervals.
Felt does not stop oil, it just slows it down so if a felt is full of oil it either needs to be replaced or washed.
There is also a gasket between the chain case & crank case which stops the oil leaking from the front.
On other models there was a stiffening plate inside the inner chain case to prevent the chain case distorting .
M20's do not have this so making one will help keep this area flat so it can seal.

Finally do not over do the primary oiling and watch fr wet sumping.
WM20's do not have an oil seal between the engine and the primary chain case.
If the oil drains from the oil tank into the sump, as soon as it gets to the height of the bearing it trickled through and over fills the chain case.
Put some rubber tube on the end of the copper breather pipe and run it well down the frame .
A lot of leaking chain case oil is actually coming from the breather.
And like the chain case over filling when the bike wet sumps, the breather will blow a lot of oil out if the sump is full of oil.

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Re: 1942 BSA M20

I took Trevor's advice & ran my engine breather line to exit to the rear of the primary chaincase. I'm surprised how much cleaner the bike stays.

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