Just took the bike for a 50 mile run.

Was pinking a bit and the plug suggests it is running really lean (would too much additive in the petrol do this - measuring was never my strong point).

However, 5 miles from home it coughed, spluttered and banged and now the points are not turning (though they turn by hand, but don't seem connected to the engine).

I have not had time to take the timing side case off yet, but guess that it is some timing cog that has gone.

Regards

Pat

email (option): sacombsashtrees@hotmail.com

The nut that holds the mag pinion to the shaft of the mag had come undone.

So timing needs to be done.

Which way is advance and which way retard on the advance/retard lever? The lever pushed away from the bike or pulled towards the handle bar?

Also, I am guessing that there are no marks on the mag pinion, so as long as the valve timing gears are aligned, the mag pinion can go in without any notches being aligned?

Thanks in advance.

Kind regards

Pat

email (option): sacombsashtrees@hotmail.com

Hi Pat...Look on the 'technical section' of the website. There is a comprehensive guide to the theory and practice of ignition timing there..(under 'Ignition Timing')...Ian

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

Check that your gear on the end of the magneto hasn't got a crack in it, they sometimes crack and this could cause it to come loose. If it is cracked I have a couple of spare ones

email (option): davmax@ntlworld.com

Have any of those gears ever been made of metal?

email (option): unpob@yahoo.com

Pat if you have the correct mag fitted to a WM20. The adv/rtd cable will be at the back nearest the battery. In which case you pull the lever towards you for full advance. If your cable is at the front nr cylinder, then you push it away for advance.
But Ian's instructions on the technical page will give chapter and verse. Ron

email (option): ronpier@talk21.com

Thanks again guys!

No crack in the Mag Pinion, so I guess it wasn't lapped in.

Next step order an extractor as I guess I wont get it right first time.

I will be using the depth bit of my micrometer to check 7/16th BTDC as I don't want to take the head off again.

Again, thanks for all your help.

Kind regards

Pat

email (option): sacombsashtrees@hotmail.com

I've found the best thing to use as a gauge is an Allen Key. Mark it at the top of your cyl head hole with the piston at TDC with a junior hacksaw. Then mark it again 7/16" above. The L shape prevents it falling down the bore. If you get it spot on first time......."You are a better man than me Gunka Pooch" Ron

email (option): ronpier@talk21.com

The cable is at the left hand side of the MAG with the points turning clockwise, so I pushed the adv/ret cable away from the handlebars.

Bike started third kick......though I am not sure if this means the timing is spot on!!!!!!

email (option): sacombsashtrees@hotmail.com

In that case you have what we call slack wire advance. Actually it's a better idea. If the cable snaps you will automatically be at full advance and therefore carry on regardless. The points should just release a fag paper as the piston reaches 7/16" BTDC. If you are unsure, it's best to double check. Ron

email (option): ronpier@talk21.com

When you are very close to this fag paper point but not exactly right, you can tinker a little with opening or closing the point gap a little to get there. But don't make the gap either to small or big.

Easy trick I use myself every time and often I get it right in one go.

Henk

email (option): ahum@quicknet.nl

I can't help but ask how on earth did you go on a 50 mile run without knowing which way advance & retard is on your handlebar lever... anyway
.. the simple way to rule out all confusion when determining which way is advance on an M20 is to look at the points Cam plate while moving your lever & when the Cam plate is moving anticlockwise your advancing the ignition.

In answer to your question Cycle Fred, I just did.

email (option): sacombsashtrees@hotmail.com

: D ... was only showing concern for your engine its really bad to run in retarded position.