Hello

I’ve been struggling on and off for 2 years with a non-starting M21. The bike ran when I purchased it in 2010 but soon afterwards, I now believe, the timing slipped on the taper and I have since then been unable to start & now time the ignition on the bike. Whilst in my ownership I have clocked up 1 mile in 3 years!

I initially thought the problem was the carb which was a very well worn Amal 76. I replaced this with a new shiny new Burlen 276 but it made no difference. After completing another project I turned my attention back to the M21 but my attempts to get it going have been in vain. I’ve tried all the obvious things such as new fuel, I have a spark etc but I can’t get it fired up.

I’ve tried all the tricks mentioned in Ian and Henks timing guides but each time the timing slips when the pinion nut is tightened on to the magneto. When I go back to check the timing it’s closed up to near TDC rather than the 7/16” BTDC it had been set it to. I’ve even tried setting the timing at various points like 1.5” BTDC hoping it will slip into position but without luck.

I’m now convinced it’s either my lack of skill/knowledge or the bike, which came from Africa, has been cursed by a witch doctor. Either way I’d really appreciate either additional tips to stop the timing from slipping or possibly if someone lives near enough (I’m just West of Reading, Berkshire) some hands-on help even if just to confirm I’m not going mad. Sadly as the bike is immobile I have no way of transporting the bike elsewhere.

Can someone assist before the bike ends up on eBay as parts?

Thanks
Gerard

Is the taper on the magneto in good condition? Another thing to check is if the timing pinion has a hairline crack in it (you have to really look at it closely)this would explain why the timing is slipping. You say you've done a few things to it but you didn't mention if you have drained the oil from the crankcases which after a year or so would seriously hinder easy starting. These are just a few thoughts to start with.

email (option): davmax@ntlworld.com

Hi Gerard,if the timing continues to slip ,there is obviously a problem with the drive pinion.first check that it is not cracked.secondly check that it is not bottoming out on the end of the magneto shaft.thirdly lap the taper with some fine grinding paste until you have a nice grey matt finish on the shaft and pinion.
also of importance is the advance retard system on your magneto.there is a tight wire ,and a slack wire type.IE with the tight wire type,as you pull the handlever towards yourself,the cam plate will turn anti clock,so advancing the timing.
with the slack wire a spring keeps the camplate fully advanced and you pull against it to retard the timing.in this way if the cable breaks you can run as your timing is advanced already.
hope this makes sense
cheers rick

email (option): richardholt@rocketmail.com

Hi Dave & Rick

I haven’t drained the oil, I'll give that a try tomorrow. The bike does have an anti wet-sumping valve but I’ll still check. Even when this is done I’m not convinced the timings not out again.

I have tried another pinion, albeit second hand, but that didn't make a difference. I'll check the original and the replacement for cracks. I’ve tried taping the pinion on, tightening slowly, progressively, quickly using Loctite + tightening slowly over several days all to no avial

The shaft of the mag looks good, I ground the pinion to the shaft. The mag is a recon unit – not that this means anything. My mag is the original type where the cable enters on the right if viewed from the points end. I believe this is the undesirable one should the cable snap.

Gerard

Hi Gerard

I had a cracked pinion & only for Dave I would never had made it to France in 2009

It can sometimes be barely visible

I also took poor advice and used loctite, what a disaster that was

I'm in Datchet jct 5 M4 so if you need to try another pinion or run through the timing, you are not that far away

07762 77219 if you want to call or text

Best regards

Jo'b (job)

email (option): Jonnyob1@googlemail.com

Gerard, I've had similar woes with my own WM20. Ultimately, these things just go back to first principles, so you need to assume nothing and question everything.

You didn't mention the spark plug or the HT lead, for instance. Just because you can see a spark, that doesn't mean the spark is working under load. M20s are low compression, of course, but I've had plugs that sparked in open air, but weren't happy in the engine.

And the carb you bought? Is it clean and operating properly? Just because it's new doesn't make it suitable (although even a poor running carb should get it fired). Is the carb slide too high, thereby admitting too much air?

The oil in the sump is a likely candidate. I've had that too. It slows down the crank speed and won't help where other things are marginal.

Is the float l level correct or is the engine repeatedly flooding?

Is the valve lifter positioned wrong and losing compression?

As I said, it's first principles. Test everything. Substitute whatever you can. Challenge everything. Then stick it in a box and send it to Ian.



P.S. All this assumes you get that timing sorted first.

email (option): dannydefazio@sumpmagazine.com

I dont want to tell you how to suck eggs but are you timing it on the right stroke

email (option): cooperbaumber@yahoo.com

Symptoms as described can sometimes result from the magneto shaft moving in the armature.
In Magdynos and other "road model" Lucas mags the steel shaft is pressed into the brass end of armature, some competition and all aircraft mags have an integral shaft, usually made from non-magnetic stainless steel.

Prior abuses, such as using a hammer to fit the pinion to taper, can result in shaft loosening (and bearing damage).

If shaft is really loose you may be able to rotate the armature by using your fingers on the points assembly.

email (option): n.gentner@bigpond.com

Thanks for the replies so far, I've got some things to check tomorrow now.

I originally tried to time the bike through the small hole in the head but in the end I took the head off. As such I’m sure I’m on the correct stroke. I even made an electronic timing tool to get the point opening spot on.

I have a new plug, lead and cap. I can't remember the plug number off the top of my head.

The carb is jetted etc as per the hand book and was ordered for the bike. When I ordered it I was told it would be set up for the bike. I haven’t messed with it too much as to be honest I wouldn’t know how to set it up from new any better than Burlen. The starting problem 'started' before Ii changed the carb though. The fuel tank is not rusty or had sealant in it and the fuel is fresh.

One thing Rick mentioned was the pinion not bottoming out on the shaft. How much clearance should there be between these two when seated? If this is worn I would assume the wear would occur on the pinion not the shaft as I'd imagine this is hardened. If it is worn can it be built up or packed out or is it another rebuild with a new armature or possibly another pinion?

John - I'm interested to hear what happened with the Loctite!

Hi Gerard, the pinion bottoming out ,could be that it has been lapped before
numerous times etc and has moved up the shaft towards the end of the taper
therefore when you tighten up,you are locking against the shoulder,not the taper.
if that is the case you will need to remove some material from the end of the pinion,so there is a gap between the shoulder and pinion.
i dont know if the pinion is hardened,so you may be able to skim a bit off in a lathe. if not out comes the grinder .
dont be scared it wont matter if you remove a little too much ,or if its not perfectly flat faced. just dont go into the seal area.
cheers rick,good luck

email (option): richardholt@rocketmail.com

Hi Gerard,
You're almost exactly where I was with my 1939 WM20 last year. Ready to scrap the damn thing and by something japanese (Ok maybe that's going a bit far!)
But I know exactly how you feel and I sympathise. I learnt some good lessons and there are some things to bear in mind:
1. These bikes don't use rocket science - everything is fixable
2. The advice and degree of good will on this forum is unbeatable. There are some real 'legends' and good guys reading our cries for help and they always have good advice!
3. There is a light at the end of the tunnel. You WILL fix it and when you do you can settle down to some great motoring - and hey, summer's on the way (I rode mine in top work today!)
Kep the faith!
Kimble

email (option): Kimble.west@bridgezoneltd.co.uk

The end of the tether has been reached!!

I just spent the afternoon and evening trying to time the bike. Each time it slips when I do up the pinion nut. When I recheck everything the points are opening at about 0.1” BTDC or after TDC. I’ve even tried setting the timing at various points (such as 1” BTDC) hoping it will slip in to place but without much luck.

I got the pinion ground back (it is hardened) as it did seem to be bottoming out but after lapping it for ½ hour it still won’t tighten without slipping despite being a good fit with clearance. I've checked for crack in both pinions by eye and using the DIY white spirit method and they seem to be good.

In reality it can only be the pinion, nut or the mag but I’m so disheartened with this issue and hence the bike I suspect the bike will be up for sale tomorrow, I just don’t want to spend any more time or money on it. I've had it 3 years and it's done 1 mile most of which has been trying to bump start it or moving it around the garage.

I thank all those who offered advice, most of this I haven’t looked at yet (such as oil in the sump or the carb set-up) as the main issue, at the moment, is a slipping pinion.

I’m going to visit a friend tomorrow to see if he can advise further but I think my time with this bike has probably come to an end.

Gerard

I hate to read of a man suffering like this. I have a certain attraction to all pre-war motorcycles so I'm prepared to offer you a hundred quid for it which you could put towards a nice period Norton (They have chain driven mags and the cover is only held on by two screws!)...

A hundred quid for a guaranteed non-runner that almost certainly is possessed, You are a generous man indeed Rik! :-)

I've followed this thread but not contributed due to the speedy and useful posts that always bet me to it with better suggestions. But I do sympathise and identify with the problem - having suffered similar problems on a totally different machine over most of the winter. I have got there now though having followed a similar approach to that suggested. My problem turned out to be a combination of slightly bent camshaft, slightly kinked points backing plate and mounting lugs, a worn cam and inaccurately made brand new pattern points! I've lost count of the full number of days I spent getting to the bottom of things. Even at this stage try not to give up mate! It IS solvable.

I'll go to a hundred and ten :-)

email (option): cruiserchooser@hotmail.co.uk

Is it not time to take it to a bike shop or another experienced forum member, there must be one close to you that would be willing to help, where abouts are you located? I hate to see someone give up when it is probably just something relatively simple that maybe just a pair of fresh eyes would spot quickly. Why not see of someone in your area would help?

email (option): davmax@ntlworld.com

Is the flat washer that sits under the timing pinion nut present?

email (option): spacemonkeym@gmail.com

hi Matt,you beat me to it,i was just thinking that myself.hopefully that is it
cheers rick

email (option): richardholt@rocketmail.com

Hi Gerard

I'm about on Sunday if you want me to pop out to help you sort this

I have all that you might need here, pinion s, points, contact breakers , timing tool etc and experience from doing incorrectly and eventually after time & good instruction, the correct method

You have my number from a previous post

My loctite issue came about as when the pinion was split it spun on the shaft and the locking nut (with loctite) couldn't be undone easily - result a damaged magneto :-(

Don't give up !!

Jo'b (John)

email (option): Jonnyob1@googlemail.com

I'm more than willing to have a look. I just don't fancy the drive from Poole to Reading. Ron

email (option): ronpier@talk21.com

What I found helped was another pair of hands. One person got the points in the right position BTDC and held the points still by hand. The other person then tapped the mag pinion on using a light tap of a hammer and a suitably sized socket. Finally, the lock nut was tightened, but careful use of a very large screw driver was used to lock all the gearing in place.

I used a bent over nail to mark TDC and 7/16th BTDC, though make sure the point of the nail is filed smooth so as not to damage the piston.

I also put the bike in gear and knocked the wheel backwards and forwards to get the correct settings on the nail.

It did take me several goes to get it almost right.

email (option): sacombsashtrees@hotmail.com

patrick i had visions of your mag ending on the other side of your workshop when you friend hit it with a hammer

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

Setting the timing accurately & then everything moving when tightening is frustrating & amature threads that are not free running can also hinder.

I found a fix that works for me.

I set the timing with a SPRING washer only under the nut, When the nut is tightened the spring washer holds everything in place by creating increasing resistance. when fully tightened & the timing checked I simply undo the nut & replace the spring washer with the correct one.
Nothing will change as the tapers should stay locked.

(if it doesnt stay locked while you swap the washers over, the tapers need attention as they alone hold the joint from turning, all the nut does is to stop the pinion coming off).

I had to grind off a mm from back of timing pinion because it was meeting magdyno bearing before tapers lock it.

Kalle

To stop the pinion sliping sprinkle just a little bit of chalk dust,baby powder on the shaft. When you do the nut up it locks the two parts together and they will never slip.

email (option): bbeyer1@optusnet.com.au

Listen to Kalle. Had to do it myself.