When mounting, how to tell when mag is correct forward and back. I have moved to where it appears correct. There just doesn't seem to be a definate place for it. The face of the mag is about 1/4 inch from the back of the timing case. I put the gear on the mag, not taping it to where it locks in place and the gear is maybe 1/8 inch farther in than the idler gear it meshes with.
Also on timing it says to set 7/16 inch BTDC + the amount that piston likes reaching top of cylinder. The example used .010. My piston likes .025 reaching top of cylinder. Does that sound unreasonable amount? There is no looseness in the rod bottom end or wrist pin that I can detect which could cause the .025.

email (option): ldj1002@yahoo.com

Hello L.D.

The missing space is not too bad, it's like 0.6mm.
It could be there because of the piston,
(May be the pin is a bit closer to the top in a pattern one)
Or due to a thicker gasket at under the barrel.

The meaning of 7/16" under T.D.C. plus what's left to the top is
Simple: 7/16"under the top reach of the piston,
So you can just take the piston up to its top/highest point,
Whatever it is under the barrel's top face, and use it as your "0" point,
And measure 7/16"/11mm down from there.
At that point under T.D.C, the magneto points should just start to open,
When it is set to the correct maximum gap.
(you can fix it to the correct gap before even starting the timing process, even on the bench table)
All of this should be done with the ignition fully advanced.
(Slack or tight type advancing, depending on your magneto)


Allot on this subject on the technical section of the forum.

http://www.wdbsa.nl/download/Ignition%20setting.pdf

http://www.wdbsa.nl/ignition_timing.htm


Good luck,
Noam.

email (option): noam10@gmail.com

OK I got her timed and attempted to put gear on magneto and it won't seat on the taper enough to stick. I waited to do this till my puller came since I'm sure I'll need to remove the gear several time to get gear mesh right and all. The magneto just isn't stucking through for the gear to go on without hitting seal. How can I tell when the mag is mounted right ie in enough? How far from the gear housing should it be? The way the slots on the engine are, the lugs on the mag could let it move fowward or back. If I get it too far forward it will be raising the mag some as it rides up. Anyway I sure I could figger it out but if someone would give pointers it will save lot of trial and error.

email (option): ldj1002@yahoo.com

Hi LD,are you sure you have the Lucas MO1 magneto? that is the correct one for a BSA WM20.Yes the slots govern the distance from from the timing case.There are
however factory made shim plates to lift the magneto slightly to give some backlash (free play) in the gears.This would have been originally done at BSA,
But as time goes by people mess about with things and bits get lost.
Get the magneto into a position you are happy with by shimming it with paper or card.When you are happy,change the thickness of paper or card for either metal shims,or plastic laminate.As a warning,I have never seen more than a few thousandths of an inch under a magneto.Hope this helps
cheers Rick

email (option): richardholt@rocketmail.com

LD you shouldn't have that 1/4" gap between mag and case. It should be almost touching. Your pinion should be in line with the idler. This is probably why it's not grabbing on the taper. Maybe the pegs on the bottom of your mag are too long? I would take it off and do some dummy runs to get it seated properly before you tighten the clamp. While you have it off, lightly lap the pinion onto the taper with fine grinding paste. Ron

email (option): ronpier@talk21.com

I have lapped the taper with the pinion. I'll check to make sure the mag is the correct one. I now think thosr pegs might be too long or maybe not seated good in the mag. Anyway now I know the mag needs to be nearly touching the timing case. I do what is necessary to fit it there.

email (option): ldj1002@yahoo.com

The mag is the correct one. How do I say this? When I first mounted mag the distance between mag and timing case was not even. I had to pull mag back that 1/4" to get distance parallel. This time I slide mag forward and twist mag so shaft sticks through seal hole centered. The distance between the mag and timing case is now close but looks crooked(see photo). The pinion goes on and locks and all from timing side looks good. There is play between mag pinion and idler gear and no shims under mag. How much play is too much? If too much, what can I do about it.

email (option): ldj1002@yahoo.com