Magneto chain wear

I can remember having to  do the same on the  coil ignition Atlas  that someone had fitted an old mag to.   

It's a nice oily dust free environment so they should last pretty well. But anyway...there were some out of tolerance cam chains (by Renold) some years ago. One I bought measured up fine with the crude means at my disposal but it would not fit. It was bar tight. Hopefully those have gone by now. The Dommie cam tensioner is just steel. It doesn't last forever and the steel bits must end in the engine oil! I really must buy a magnetic sump plug one day....some keen Commando owners fit an automatic cam tensioner. I worry that an eccentric sprocket plus temperature changes might lead to them becoming too tight?

Hi David,  Now I am worrying about my cam chain that I have not seen for 25 years !  .  I think this Pandemic has turned  me  (us?) into  a worrier.  Lets us all try to get out more on our bikes  this  summer. We need it. .  

If any chain wears badly its links will have stretched and the sprockets need to be looked at for wear.  The worst chain for wear is the rear driving chain which is exposed to all things nasty!  If that stretches, and has been run for quite a few miles, you are likely to need a new rear sprocket/brake drum (Ouch!) and a gearbox sprocket.

A slack chain will also wear out the sprockets more quickly too.  Of course, worn sprockets will wear out chains.  A vicious circle!

Does anyone know if you can chain the older plain steel tensioners for the rubber-faced type?  If so, is it worth it?

Hi Peter, 

Knowing that you have timing 'issues' and a mag rebuild has been encouraged, what state is the sprocket/ATD unit? Is this where your chain issue is? Have to say that is just a guess as I went electronic on mine so have no experience of a mag. Hope you find out what the cause is.

To answer Lionel's question, the "rubber" (ok, may not be rubber, but it is black and  not fully hard) cam chain tensioner is a straight swap on a dommie (well it was on mine), only minor issue with it is having to retension the chain after 3-400 miles or so as the chain 'beds in' to it, which would take forever with the standard one. Once done, no chain noise from the timing chest anymore, and as was intimated above, no  bits of steel coming off the tensioner.

Regards, George 

My mag chains have not stretched as far as I have observed. I bought a new one for the Dommie after about 25k miles before I took the cover off. Waste of money. But that's just one anecdote.

Glad you've solved it Peter.  I realise you were talking about the cam chain in particular and I was bringing in the general subject of chains, but it's always worth checking the sprockets for hooked teeth - even if only mild.

Thanks George for info about the rubber faced tensioners.  I had figured that there would need to be some slack whilst bedding in.

Jaguar XK Series engines also use rubber-faced tensioners on their timing chains but most parts for those engines are cheaper than Nortons!  E.g. Valves - £6.40 exhaust, £4.30 inlet!  Oil pump £53.59.  Sadly it won't fit a Norton!