I’m in the final stage of re-doing my M20, preparing it for mothballing: replacing some pattern parts by NOS ones, new wiring and LED-lights, the magdyno rewound etc...
But I have a - hopefully not too serious - problem with that magneto: I fear that the taper on he shaft is too short, and it shows when the nut is tightened. Then the magneto driving pinion 65-2334 is about 1/8" shifted inwards from the idler pinion 66-2250 , so they engage for about 60%. I suppose that should be enough...

That's strange Hans,
what was it like before you took the ignition off ?
Cant you just move the ign over a little bit ?

Han's I agree with Michel! There are slots in your mag platform to enable you to get the mag in the correct position. I don't think the taper shaft can be too short as the pinion wouldn't lock onto it......Take another look at the position of your mag..... Maybe even the pegs underneath? Ron

email (option): ronpier@talk21.com

Hans,

I have had a magneto drive pinion that was split at the taper. So it you tightened it the pinion would move towards the magneto by opening the split. it took me ages to find this but in the end the timing went off every time because the pinion turned when the engine kicked back. I have since then found one other pinion with a similar split on the taper.

Kind regards,
Leon

email (option): leonhop33_at_planet_dot_nl

No Ron, it's so close that I can't get a feeler blade in between....
Perhaps I need another armature; pity, it has just been rewound

Well I just measured a spare mag with a vernier and the taper including thread is about 23.3mm. I don't understand how your pinion can lock onto the taper if it's too short. Plus the pinion is nearly butted up to the mag at the end of the taper, so don't know where you are losing 40% of your meshing.

Ron

email (option): ronpier@talk21.com

No Leon, no split ! I tried my spare NOS one, same result

I measured also: 22.9 mm, threaded lenght 11.4 mm. But looking at the taper there are signs it has been tampered with...
Now, what can I do? I can butcher two pinions: one to use the taper and make a bush, and reaming out the other pinion to receive that bush, and loctite/solder it 3mm protruding to the magneto.
Nice bodge, I have the tools and the time (I hope so at least) and cheap but no guarantee it will hold on forever.
The other solution: find a good used armature, and have it rewound. Anyone ...

Forgot to ask: what's the taper on the armature? Do reamers exist for it, like the Morse taper ?

Hans in my opinion the "bodge" that you speak of is not going to help anyone in the future. Maybe be better to swallow the pill and find another armature.

I've just taken a look at another spare armature I have. Total length of thread and taper to the inboard threads is about 24mm with the thread at about 11.5mm.

I'm not looking to part with it, but would do for you Hans if you're stuck. You could have it as is or I could get a price for my guy to rewind it. However there is always a 6-7 week queue with him. Ron

email (option): ronpier@talk21.com

PM send !
Hans

['Forgot to ask: what's the taper on the armature? Do reamers exist for it, like the Morse taper ?']

The taper on the mag armature is 1 in 10 or expressed in degrees 11.42 degrees inclusive...Ian

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

Thanks Ian, I'll make a note in my documentation

Hi Ron,
This morning I compared my magdyno with one of a friend, and it shows exactly the same shift (about 3 mm) in meshing of the magneto and idler gears. And the magneto driving pinion is about half a mm from the magneto body.
So, unless somebody shows us a magneto with the pinion about 3 mm from the body, and 100% meshing of the gears I take it that this is a normal situation...

Well I said that yours looked ok to me Hans. Unfortunately I don't seem to have a picture of the inside of my timing chest to remind myself what mine looks like, and not about to take it apart till I need to. However I don't remember any miss meshing. Maybe your first estimate of only 60% meshing was a bit pessimistic Ron

email (option): ronpier@talk21.com

Stupid me....
I forgot that reinforcing ring between the magdyno and the carter; thick 1/8" which explains the 3mm shift in mesh of the magneto pinion and the idler...

Hello Hans.
I also have one motor with this fix of plate lie somewhere,
But as far as I remember, the plate is flush with the engine's body,
And anyway, the thread seem very short inside the nut in your photo,
And it has nothing to do with the plate, as the mag gear/sprocket
Does not touch anything but the oil retainer around it...
Strange...

Noam.

email (option): noam10atgmail.com

There are 'long' and 'short' versions of the magneto nut...The M20 should use the short one to be correct...but perhaps Hans has the longer nut fitted?...Ian

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

Stupid me....
I forgot that reinforcing ring between the magdyno and the carter; thick 1/8" which explains the 3mm shift in mesh of the magneto pinion and the idler...

Helped by friends from the M20 scene (Thanks Erik and Adrie !) we attacked the Magdyno problem again by carefully setting the ignition, ending with a firm rap on the pinion, but without tightening the nut yet. This seemed to be enough to securely lock the pinion and magneto tapers together, as they should. But turning the rear wheel slowly, there was a slight wobble visible in the pinion, and surely, the pinion had worked loose and could be removed by hand.
There were signs of rubbing on the pinion and the reinforcing ring.

Conclusion: although the magdyno is securely against the case, that 3 mm reinforcement ring is enough to prevent both tapers to lock together.

So I have these options to get my M20 on the road againn:
1- use the appropriate type of Loctite on the taper, to move the pinion that fraction of a millimetre to prevent the pinion from rubbing the oil seal seat. This is the kind of Middle-East and Asian bodge; the only advantage is that it is not permanent, pinion can be removed by heating, but will it be sufficient in the long run?.
2- use a thin sleeve that fits the tapers to move the pinion sufficiently (about 3 mm), and glue it either inside the pinion or on the magneto taper with Loctite. Making such a thin tapered sleeve is not impossible but beyond my capabilities.
3- find another crankcase, without that d*****d reinforcing ring, transfer all those parts and then get it in the frame again . Advantage is clear, but spending another winter in the garage, getting the gearbox and engine out and in again, and always with the risk that I kick the bucket (I am now 85!:innocent: ) before the final adjustments are done.

I have the intention to leave this bike to my grandson Stan, age 17, who is in the final year of secondary school, and has no time at all to learn the finer points of M20 mechanics. He has to wait until the age of 21, for riding a motor of up to 11kW and 500cc capacity....
Fortunately, both my daughters have the right papers and are eager to fill his place in the saddle, but both have to learn even more than Stan about the BSA.

Hans I can only think that, that REME modification must have worked satisfactorily every time with a standard mag, pinion and tapers? Ron

email (option): ronpier@talk21.com

Ron, is this a standard modification by RME ? Are there others known ? Noah has one, but it is flush with the engine face. Any suggestion is welcome to cure this !

Hans I'm fairly sure that Ian has mentioned this REME mod in previous posts. Didn't your bike always have a functioning mag with this engine case? Ron

email (option): ronpier@talk21.com

Ian, where are you when I need you....:scream:

Until now, no reactions whatsoever....
Is my carter the only one in the world with that reinforcement ring for the magdyno? Could it have been for a special model: stationary, agriculture, with another magneto? Any info is welcome !

This is indeed a REME modification that was carried out to repair a worn magneto seal housings...I've had a number of WD crank cases with this worked done...Sometimes the plates are steel and sometimes brass but the dimensions and fitting procedures are broadly the same....

I don't quite understand how you ran the bike previously with this fitted, or did you just ignore the misalignment of the gears?..Have you changed the crank cases?...Ian

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

Thanks Ian, but where these reinforcements flush with the crank case, or did they stick out for about 3mm, as can be seen on the photo of August 17th ? This sets back the magdyno for the same amount, and causes my problem...
I changed the crank case some 4 years ago, since it was in better condition than the old one. Shortly after that, I got health problems and since then I have not ridden the bike.:cry:

If the back of the magneto drive gear is engaged with the oil seal OK and there are no other problems I wouldn't worry too much about the gear alignment....The Gold Star runs a much narrower idler wheel as standard without any issues and I've thinned down all the gears in the past when tuning OHV engines....(that make a lot more power)

I can't say I paid much attention to how far the 'repair piece' protruded from the back of the crank case...I guess you tend to look at these issues when you have to...

I'll have a look to see if I currently have any cases with the part fitted and if I have I'll post the results later...Ian

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

Here is another one of those REME repairs. I can't remember who's engine it is though? Ron

email (option): ronpier@talk21.com

One thing that nobody mentioned yet? is that you can put all the spacers/shims on the bearings on the magneto armature on one side, so the shaft sticks a bit more out.

Might just do the trick!

Cheers,

Lex

email (option): welbike@welbi(XX).net (think about this!!)