Tight spot magneto drive chain

Singles, twins and fours.
User avatar
alan.moore
Holder of a Golden Anorak
Holder of a Golden Anorak
Posts: 1345
Joined: Sat Jul 19, 2014 1:29 pm
Location: Leicestershire UK
Contact:

Tight spot magneto drive chain

Postby alan.moore » Tue Dec 10, 2019 6:01 pm

Gents
I have just fitted a new Magneto chain to the WNG (endless from John Budgen) and find that there is a significant tight spot. Slackest point I have 1/2" of play and tightest no play. Odd thing is that the tight spot only occurs every one revolution of the sprockets i.e if I mark the top of the sprockets when the chain is tight and then rotate the tight spot only occurs when the sprockets are in the same position. The chain itself is in different position each time the tight spot is reached which leads me to think that it is not the chain.

I have measured the distance between the sprockets / mag spindle / cam spindle for runout and there is nothing significant.

The sprocket teeth appeared OK when I rebuilt the engine but a bad tooth/teeth on one or both of the sprockets is all i can think of to give the symptoms I have.

Anyone any ideas?

Cheers
Alan
1939 VH Redhunter;1942 RN WNG;1951 Triumph 6T Thunderbird;1970 BSA B175 Bantam;1986 Yamaha SRX600 single
http://cloggymoore.wix.com/triumph-pre-unit-6t

User avatar
chris.shearwood
Holder of a Waxed Cotton Anorak
Holder of a Waxed Cotton Anorak
Posts: 495
Joined: Mon Feb 28, 2011 5:28 pm
Location: Sutton, Quebec, Canada
Contact:

Re: Tight spot magneto drive chain

Postby chris.shearwood » Tue Dec 10, 2019 7:38 pm

Bent mag armature shaft?
1946 4G, 1950 NG and 1951 VH

User avatar
alan.moore
Holder of a Golden Anorak
Holder of a Golden Anorak
Posts: 1345
Joined: Sat Jul 19, 2014 1:29 pm
Location: Leicestershire UK
Contact:

Re: Tight spot magneto drive chain

Postby alan.moore » Tue Dec 10, 2019 7:40 pm

Chris,
Nope, mags only just been reconditioned by Tony Cooper and checking with a dial gauge its true.

Cheers
alan
1939 VH Redhunter;1942 RN WNG;1951 Triumph 6T Thunderbird;1970 BSA B175 Bantam;1986 Yamaha SRX600 single
http://cloggymoore.wix.com/triumph-pre-unit-6t

User avatar
chris.shearwood
Holder of a Waxed Cotton Anorak
Holder of a Waxed Cotton Anorak
Posts: 495
Joined: Mon Feb 28, 2011 5:28 pm
Location: Sutton, Quebec, Canada
Contact:

Re: Tight spot magneto drive chain

Postby chris.shearwood » Tue Dec 10, 2019 7:42 pm

Alan,
Do you have another mag sprocket to try?
1946 4G, 1950 NG and 1951 VH

User avatar
alan.moore
Holder of a Golden Anorak
Holder of a Golden Anorak
Posts: 1345
Joined: Sat Jul 19, 2014 1:29 pm
Location: Leicestershire UK
Contact:

Re: Tight spot magneto drive chain

Postby alan.moore » Tue Dec 10, 2019 7:58 pm

Chris,
No spare sprocket. I think I need to get the chain off and check the two sprockets for runout with the dial gauge mounted on the timing chest. I would expect to be able to see enough out of alignment for it to change the chain tension from 1/2" to fully tight but nothing obvious. Strange....
1939 VH Redhunter;1942 RN WNG;1951 Triumph 6T Thunderbird;1970 BSA B175 Bantam;1986 Yamaha SRX600 single
http://cloggymoore.wix.com/triumph-pre-unit-6t

nevhunter
Holder of a Golden Anorak
Holder of a Golden Anorak
Posts: 4091
Joined: Tue May 10, 2011 9:42 am
Location: Victoria.. Australia.
Contact:

Re: Tight spot magneto drive chain

Postby nevhunter » Tue Dec 10, 2019 11:01 pm

You might find there is off centre sprocket machining of one or both. Mount a mandril in the lathe chuck and traverse a dial indicator at the base of various teeth and you might be able to detect eccentricity (not your own) You might be able to just "lick" a few bases carefully with a dremel and correct it. Nev

User avatar
alan.moore
Holder of a Golden Anorak
Holder of a Golden Anorak
Posts: 1345
Joined: Sat Jul 19, 2014 1:29 pm
Location: Leicestershire UK
Contact:

Re: Tight spot magneto drive chain

Postby alan.moore » Tue Dec 10, 2019 11:15 pm

Thanks for the advice Nev. I haven't got a lathe only a pillar drill which i think will have too much play in the shaft.

Club spares have NOS Mag and Cam sprockets so if the Mag and Cam shafts are true (will check tommorow) that only really leaves one or both of the sprockets.

Cheers
Alan
1939 VH Redhunter;1942 RN WNG;1951 Triumph 6T Thunderbird;1970 BSA B175 Bantam;1986 Yamaha SRX600 single
http://cloggymoore.wix.com/triumph-pre-unit-6t

nevhunter
Holder of a Golden Anorak
Holder of a Golden Anorak
Posts: 4091
Joined: Tue May 10, 2011 9:42 am
Location: Victoria.. Australia.
Contact:

Re: Tight spot magneto drive chain

Postby nevhunter » Wed Dec 11, 2019 12:34 am

Might be the easiest way but it doesn't take much maggy shaft runout to give the variation you have. Is it a quality chain? with a matching 1/2 link. Depending on where they end up as it gets turned over, they can cause a variation. I prefer NO joiner, and I do all adjustments on the cam sprocket even though it involves taking the pump off. The maggy shaft is too easily moved out of alignment. ( Magdyno type) Nev

User avatar
alan.moore
Holder of a Golden Anorak
Holder of a Golden Anorak
Posts: 1345
Joined: Sat Jul 19, 2014 1:29 pm
Location: Leicestershire UK
Contact:

Re: Tight spot magneto drive chain

Postby alan.moore » Wed Dec 11, 2019 6:35 pm

Checked runout of mag and cam shafts and they run true. Checked the base and tips of the teeth for concentrically whilst fitted to the shafts, all good. However i did find some burring on the side of the mag sprocket teeth so clearly some wear evident. Have ordered two NOS sprockets from club spares as there were a reasonable price and gives me a known starting point.

Nev, the chain is endless with a riveted half link, Regina make so a branded chain. Have one on the VH and had no issues with adjusting that. I think others in the Club use the same chain (from John Budgen £13) and there has been no adverse feedback.

I agree re using the cam sprocket to set the timing, much easier than attempting to tighten the mag nut without altering the sprocket position.

Cheers
Alan
1939 VH Redhunter;1942 RN WNG;1951 Triumph 6T Thunderbird;1970 BSA B175 Bantam;1986 Yamaha SRX600 single
http://cloggymoore.wix.com/triumph-pre-unit-6t

User avatar
alan.moore
Holder of a Golden Anorak
Holder of a Golden Anorak
Posts: 1345
Joined: Sat Jul 19, 2014 1:29 pm
Location: Leicestershire UK
Contact:

Re: Tight spot magneto drive chain

Postby alan.moore » Mon Dec 16, 2019 6:00 pm

All sorted. Fitted the NOS Mag and Cam sprockets from Single Spares and chain tension is constant. Must have been uneven wear on the sprocket teeth.

Cheers
Alan
1939 VH Redhunter;1942 RN WNG;1951 Triumph 6T Thunderbird;1970 BSA B175 Bantam;1986 Yamaha SRX600 single
http://cloggymoore.wix.com/triumph-pre-unit-6t


Return to “Four stroke”

Who is online

Users browsing this forum: Gui.dorey and 9 guests