Fitting magneto to crankcase

Hi All

Thanks for coming back. I will leave the bronze washer out. I do have the correct chain I bought it new one from RGM it's a Renolds Mag/Distributor chain and it is thinner than the Cam chain. The tension on it is correct.

Can anyone tell me if there is anything fitted behind the magneto sprocket that will move the sprocket away from the inner timing cover slightly?

Regards Pete

Thanks i will try that tomorrow. I do have a cut out timing cover. Thanks again Pete

Happy new year.

I have tried Jonathan's method of fitting the magneto etc. This did make the advance and retard a little freer but when I took the slack out of the chain the advance and retard became too tight again. When I fit the sprocket to the magneto without the chain being attached the advance and retard is perfectly free, it is only when I attach the chain that it locks up. I cannot see any misalignment of the magneto chain. I have tried a spare advance and retard mechanism but this had the same result. The complete mag and advance and retard mechanism were overhauled by Brightspark and they have done a very thorough job. I am at a loss - any further suggestions would be appreciated. Regards, Pete

Hi

Thanks for your thoughts on this. I have just now fitted the magneto in place but without the chain, and tightened everything up. The automatic advance and retard mechanism is perfectly free. When I fit the chain and leave it loose it's better, but of course when I tighten the chain to the correct tension, which I believe is 3/16 approx, the A/A locks up.

I have been looking at the intermediate sprocket and that area all appears fine. I think tomorrow I may dismantle all of the timing sprockets and see if I have made any schoolboy errors while fitting them earlier.

You say the centre bolt may be too short which could then cause the A/A to be pulled in and bind but I don't think in this case that is happening as everything works correctly without the chain being fitted.

I have spent an awful lot of time on this problem and am getting to the point where I may end up fitting a manual advance and retard. I have all the necessary parts for this apart from a new chain, as I think the chain will have fewer links. The only thing stopping me from doing this is that for my own peace of mind I would like to find the explanation. Also if I can't sort this problem out there may be a knock on effect with the manual advance and retard.

Thanks again for your help.

Regards Pete

Hi Mike

The mag ia in really good condition. Brightspark did a complete overhaul on it. I know it had new bearing and anything else it needed.

Thanks anyway Pete

Hi Jonathan.

I did check that lower waisted stud a little while ago and again this morning and it isn't touching the chain. I have attached an image which shows this. I have loosened off the chain so it can be seen better, but even at the correct tension the stud hasn't touched the chain.

I am sure now that the Mag is in very good condition thanks to Brightspark and that the mag is mounted correctly. As the problem only occurs when I add the chain I think it may be an alignment issue. Even though it all looks right. Tomorrow I will strip down all the timing sprockets with particular attention to the intermediate sprocket. I do have two other intermediate sprockets I can compare with. If all this fails to cure the problem I will fit a manual A&R and admit failure.

I will up-date these notes tomorrow evening. Thanks very much for all your contributions. This is such a straightforward problem that I feel bad that I haven't been able to solve it.

Regards, Pete

Attachments
mag-1-jpg

Hi.

The hardened thrust washer is fitted and the large grey washer came with the A/R unit and is shown in my Haynes Manual. I have removed the washer but it didn't make any difference so I am not sure what it does.

Regards Peter

Hi.

My son in law found the same problem listed in this message pages dating back to Sept 2014. I have now adjusted the Mag chain tension to allow the AA&R mechanism to work freer. The chain tension is not as tight as the manual spec. but I feel it is an acceptable compromise!

I have taken the liberty of adding the reply from Jim Hill

"Sept 2014: I had the same problem with my dommie following a rebuild and it took me a bit of time and thought to realise: the AAU is not malfunctioning, it has stopped in the fully advanced position and in reality the bob weight springs are trying to turn the whole engine to catch up with the magneto which of course they are incapable of. When you remove the timing cover don't take off the AAU but just rotate the engine forward slightly and you will find that the mag doesn't start to turn until the bob weights are back in the retarded position, ready for the next start. The above assumes the chain tension/alignment is good, if you think about it long enough you will see that it was always thus; your starting problems are elsewhere ..... good luck, Jim Hill"

It will be a month or two before I run the engine so I will not know if this has worked until then. Thanks to everyone for your contributions/suggestions. Pete

Hi

Just to finish this one. As I said earlier I adjusted the chain so that the AA&R moves freely without the mag. chain being as tight as the manual shows.

My bike is now complete and the engine runs very well with no problems from the AA&R.

Regards Peter