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Author Topic: magneto chain tension issue with all new parts  (Read 271 times)

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Greybeard

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Re: magneto chain tension issue with all new parts
« Reply #11 on: January 16, 2019, 11:58:24 AM »
@ Steve, I wonder if you had to alter your mag chain case, now using a 49 link chain?

Hello, Winold. Sorry for the late reply. No I didn't have to alter the cases and there was no sign of them ever having been altered. In fact the chain that came off was a 49 link. As I said, Sprockets Unlimited also have 49 links recorded as the correct length for my Lion.
As long as you have it sorted now, that's the important thing  :) Good luck with the rest of the rebuild.

Steve
1937 Sunbeam Lion 500cc
1952 BSA A10 Golden Flash
1953 Matchless G9 500cc
1953 BSA B31 350cc
1958 Ariel NH350 Red Hunter
1961 Matchless G80 500cc
1961 AJS M31 De Luxe 650cc
1982 Moto Morini 3 1/2
1992 BMW R100RT
2007 Triumph T100 Bonneville
1960 Rover P4
1979 Triumph Spitfire

Rick Parkington

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Re: magneto chain tension issue with all new parts
« Reply #10 on: January 13, 2019, 07:11:50 PM »
Hi Winold,
Now you know why choosing to rebuild 1920s bikes from hopeless basket cases will never make me a wealthy man!
Glad to  hear you are progressing...sort of!
Cheers mate
Rick 

Winold

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Re: magneto chain tension issue with all new parts
« Reply #9 on: January 13, 2019, 06:51:28 PM »
The mystery is partly solved :D

There were some things going on. The 'ready to fit' restored mag was a bit wobbly, the bottom of the mag had some damages. A little sanding on a glass plate solved it. Then, after measuring the center to center distance from the mag sprocket to the timing sprocket on my restored engine and on a spare early 30's engine I found they are the same. So I fitted the mag on the spare engine and the chain tension turned out to be just fine. After a lot of measuring it became clear that the hole in the mag chain case wasn't high enough. It had to be filed out upwards about 1,5mm. After that the mag fitted and adjustment was easy and perfect.

You would think it would have been easy to see that, but it really wasn't. The mag was sitting flat on its rest, it seemed the sprocket turned freely. And an important part was the confusion, this engine is used, the mag chain case is not molested.. So how is it possible with a new chain and new sprockets that I have to alter the chain case? The only reasons I can come up with is that the used sprocket on this engine had a different outer diameter going through the cover. Or a different chain, not being a morse chain or a  3/8" x 5/32" roller chain.

@ Steve, I wonder if you had to alter your mag chain case, now using a 49 link chain?

Winold

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Re: magneto chain tension issue with all new parts
« Reply #8 on: December 31, 2018, 09:03:45 AM »
The magneto is on the correct height, playing with spacers didn't result in an acceptable chain tension. It couldn't be raised enough without the sprocket touching the chain case.

I thought the solution of the problem would be fitting a roller chain with new sprockets. I would have liked to use the morse chain, and I've tried. But a 50 link morse chain is too long, and a 48 link morse chain is too short. So it needs a 49 link chain, same amount of links as a roller chain. It would mean the morse chain needs a crancked link as well. I'd be interested to know if a 49 link morse chain exists and if someone knows to what bikes the 50 (, 49) and 48 link morse chains have been fitted. Does anyone know when Sunbeam has stopped fitting morse chains to their motorcycles?

wrx03ppp

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Re: magneto chain tension issue with all new parts
« Reply #7 on: December 30, 2018, 11:59:13 AM »
Is the magneto height correct? How much of a spacer underneath would be needed to establish the correct tension?

singleminded

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Re: magneto chain tension issue with all new parts
« Reply #6 on: December 29, 2018, 07:37:52 AM »
maybe there is a difference when changing from a Morse chain to a Roller chain.?

Greybeard

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Re: magneto chain tension issue with all new parts
« Reply #5 on: December 28, 2018, 06:43:56 PM »
Yes, mine did come as an endless chain with a cranked link, Winold. It was the spec that Sprocketsunlimited already had for it. Perhaps it's the parts book that's wrong  ;)

Steve
1937 Sunbeam Lion 500cc
1952 BSA A10 Golden Flash
1953 Matchless G9 500cc
1953 BSA B31 350cc
1958 Ariel NH350 Red Hunter
1961 Matchless G80 500cc
1961 AJS M31 De Luxe 650cc
1982 Moto Morini 3 1/2
1992 BMW R100RT
2007 Triumph T100 Bonneville
1960 Rover P4
1979 Triumph Spitfire

Winold

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Re: magneto chain tension issue with all new parts
« Reply #4 on: December 28, 2018, 04:21:26 PM »
Hi guys, thanks for your replies

@kbryt; the magneto moves freely between the slackest and tightest position

@ Steve; Your chain has the same specs as mine, a 3/8" x 5/32". The parts books say that it should have 50 links, which is what I have now. 49 links sounds like a 48 link chain with a crancked link, so I'll order a crancked link somewhere and see if that works on my engine as well. Still a bit weird that this spec doesn't match the parts books.

Thanks a lot! I'll give an update once I received the crancked link.

Cheers, Winold

Greybeard

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Re: magneto chain tension issue with all new parts
« Reply #3 on: December 28, 2018, 12:34:45 PM »
Hello, Winold. I've just checked the receipt that I got with my new chain from sprocketsunlimited.com and they supplied a 49 link 3/8th x 0.155" Iwis chain (cost was £14.28) which fitted perfectly. My bike is a 37 500cc SV Lion. I doubt whether Sunbeam's product development included much of a redesign in that area ;)

Steve
1937 Sunbeam Lion 500cc
1952 BSA A10 Golden Flash
1953 Matchless G9 500cc
1953 BSA B31 350cc
1958 Ariel NH350 Red Hunter
1961 Matchless G80 500cc
1961 AJS M31 De Luxe 650cc
1982 Moto Morini 3 1/2
1992 BMW R100RT
2007 Triumph T100 Bonneville
1960 Rover P4
1979 Triumph Spitfire

kbryt

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Re: magneto chain tension issue with all new parts
« Reply #2 on: December 28, 2018, 11:04:24 AM »
Can you not move the actual magneto back?

Winold

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magneto chain tension issue with all new parts
« Reply #1 on: December 27, 2018, 09:45:17 PM »
Hi everyone,

I'm looking for some help in thinking about a solution and a cause for a magneto chain tension problem. I am working on my 1926 model 7 with a 600sv engine. The problem is that with the adjustment the magneto has, the chain can't be setup with the correct slack of about 1/4". In the tightest position, the slack is about 1", see photo 1. This is a beautiful 20's original Sunbeam chain and it could well be worn. I ordered a fresh new set of sprockets and a new chain from Chris Odling. Super quick delivery to Holland made me very happy. Thinking this would be the solution I fitted them, just to find that also this new set couldn't be setup right. The minimum slack is now about 3/4", a bit better but still no good, or is it?

Thinking through all possible causes for this problem: Chris Odling has restored the engine, so it should be assumed that's all perfect. The magneto is done by a Dutchman and should be allright as well. Magneto spindle is true. The hight of the magneto sprocket is exactly in the middle of the unmolested chain cover. And now, sprockets and chain are new.

The chain has 50 links. In the slackest position for the chain it seems that 49 links could be the solution, see photo 3. So a crancked link might just do the job, but it seems a little tight. And in the parts books is written that 50 links are needed. Also a cracked link from the factory seems a bit weird. A solution could be making a spring tensioner, but before that, I'd like to here about your thoughts about this.

Have there been any more types of sprockets and chains on 20's Sunbeams and could this engine need a different chain setup? I only know of the 2 types shown in the photos.

Hope you can help. Many thanks from Holland, Winold