Broken-up Magneto Drive Chain

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Keith.owen
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Broken-up Magneto Drive Chain

Postby Keith.owen » Thu May 09, 2019 6:34 pm

Hi,
I felt as though the timing on my VH was a bit retarded even on full advance, so today I decided to check it, and yes points were opening at about 1/4 inch BTDC on full advance (well approximately because sticking something through the plug hole is not that accurate, but based on the notches on my dipping stick).

So, off with the timing cover and I noticed something in the bottom when I pulled it off - the remains of chain rollers!

The question is knowing what might cause this, since the chain was new under 3000 miles ago and was o.k. when I last tampered with the timing about 1000 miles ago (spring last year).

I think I have been lucky, because nothing got jambed and the rollers (remains of) didn't appear to get very far, but this has been pretty catastrophic from the point of view of the chain which has, quite literally 'had it'.

Assuming the chain was of good quality, what might I have done to have caused it's demise?

Anyone out there had a similar experience?

Naturally I shan't be going out on Betsy until this is fixed and there is no point just sticking in another chain only to have a repeat experience, so, I really could benefit from any suggestions.

Thanks and BR,

:shock: Keith
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Re: Broken-up Magneto Drive Chain

Postby will_curry » Thu May 09, 2019 6:59 pm

High on my list of things to worry about with an Ariel single is how well - or otherwise -
have I aligned the magneto sprocket with the camshaft sprocket. Not only can the mag
not be parallel to the cam it can also be too close to the timing case or not close enough.

When I've got it wrong in the past it's been noticeable as noisy and the sideplates of the
chain have worn rapidly. So far I haven't had broken rollers or for that matter a broken
chain. Where I have seen broken rollers and not in Ariel engines has been where the teeth
on the sprockets have been damaged. Getting the sprockets off without the proper
puller is a good way to damage them.

So my suggestion is to look at the sprocket teeth first.

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Re: Broken-up Magneto Drive Chain

Postby Mick D » Thu May 09, 2019 7:25 pm

Hi

Broken rollers in my opinion would suggest over tension, (or possibly very much under tension, but in this case I'd expect to see contact evidence on the chain case).

Regards Mick

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Re: Broken-up Magneto Drive Chain

Postby paul.jameson » Thu May 09, 2019 9:29 pm

I have had this happen, but on a primary chain. So did Lester Grant, also on a primary chain. Given that I don't think either of us had done anything serious to provoke such a failure, then the manufacture of the chain comes into doubt.

Where previously I would buy chain from anyone, nowadays I always buy from Sprockets Unlimited (as they are nice, helpful people who have never sold me a duff chain during 20 years or so of custom) and I follow their recommendation as to which brand I should buy. Funnily enough, I can't remember the last time I bought a chain marked "Reynolds."
Paul Jameson
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Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.

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Re: Broken-up Magneto Drive Chain

Postby robjameson » Thu May 09, 2019 10:41 pm

I have had this happen on timing chains before.
I have put it down to bent teeth on the cam or magneto sprockets. Sprockets unlimited suggested a few years ago using a chain which is wider (as the traditional size timing chain is no longer available from a quality manufacturer), and the extra width helps with any alignment issues.
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Re: Broken-up Magneto Drive Chain

Postby nevhunter » Fri May 10, 2019 2:53 am

Some chains actually have split rollers from new. Avoid them like the plague and some "industrial" chain is poor quality also. I have never had an Ariel maggy chain cause problems but you need to check the armature is running true as that will make setting the "slack" difficult. People prise off sprockets. Use the correct puller. line everything up carefully. The slotted holes that hold the magneto on may need attention. They get worn on the underneath surface and want to sit in one particular place. Welding it up and carefully remachining it is the only answer to getting it to adjust evenly. Nev

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Re: Broken-up Magneto Drive Chain

Postby Keith.owen » Fri May 10, 2019 10:36 am

Hi All,
Thanks for your suggestions etc.

I have emailed sprockets unlimited to see if they can help me with a new chain. Drags don't have any and further, when they do the chains they now sell have a split link; not sure what to make of that?!

I shall strip everything down tomorrow and take into account all of your suggestions, all of which seem vaild.

I do suspect a sprocket, because I recall seeing the magneto wobbling on its mounts which stopped when I employed the third bolt right up by the engine plates; maybe I missed a sign?

Keith
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Re: Broken-up Magneto Drive Chain - further comments sought

Postby Keith.owen » Sat May 11, 2019 10:48 am

Hi,
I have just removed the sprockets and chain.

Following advice from Jane at sprockets unlimited, I have examined the chain carefully and theer are no scuff marks on the insides of the links that might indicate misalignment. What I have found is that: 1) the rollers that have broken are all on the smaller 'inner' links and at irregular intervals and 2) the chain is partially seized (very stiff) in places.

There was oil in the timing cover when I removed it and the chain is moist with oil.

On the subject of oil in the timing cover, I assume it finds it's way in there as mist through the large diameter hole in the timing chest that is located toward the top and to the left of the cam spindle.

So, for the moment I can only conclude that it was a naff chain - I hope I am right. Hopefully someone can tell me if I'm not, because I don't want to go through this agsin. I guess a aseizure is unlikely, but I don't want to find myself in a situation where I have suffered damage!

Any thoughts will be greatefully received.

thanks and BR,
Keith
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1951 Rigid Ariel NH (under construction)
1973 Norton 850 Commando Interstate

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Re: Broken-up Magneto Drive Chain

Postby alan.moore » Sun May 12, 2019 10:52 pm

Re original spec timing chains I got my last one from John Budgen, it appeared identical to the one I removed which was at least 50 years old...endless with a cranked link as the original correct length chain specification has an odd number of links. £13 madew by Regina.
See photos at end of this post
viewtopic.php?f=4&t=7001&p=52981&hilit=chain#p52981

Cheers
Alan
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Re: Broken-up Magneto Drive Chain

Postby nevhunter » Mon May 13, 2019 12:15 am

Check the runout of the magneto shaft. Nev


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