Magneto

General electrical problems
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robjameson
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Magneto

Postby robjameson » Sat Jul 28, 2012 7:42 pm

I have been suffering with some issues with my newly rewound mo1.

I cannot achieve a consistent spark, most noticeably on the plug side of my vh. I have been able to get the thing sparking
Properly holding the end of the ht lead on the right hand side of the head, but as soon as I move it to the left where the plug is it stops consistently sparking. I have looked at the pick up and there is no obvious problem, I have also replaced the ht lead, but to no avail. Any ideas? Could the mag clutch be slipping?

Help!
Rob Jameson
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1957 Ariel VH
1956 Ariel KH (LARGE project!)

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john.nash
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Re: Magneto

Postby john.nash » Sat Jul 28, 2012 9:34 pm

Is this the "mag clutch" that drives the Dynamo (on top) ?
The symptoms of that not working would be that your dynamo won't put out a charge with a load (i.e all the lights). It will charge fine with no load. Been there.

I assume that when you move the lead around to where the plug is, the HT lead now passes close to the head ?
Can you ground it on something else without going near the head, and get a spark ? Might mean a longer lead ........
John "Josh" Nash
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brenton.roy
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Postby brenton.roy » Sun Jul 29, 2012 3:11 am

Hi Rob,
If moving the lead to a different position affects whether or not you have spark, and you have changed the lead, it suggests the pickup. There is nothing else you can affect by moving the lead.
Damage inside the pickup wouldn't necessarly be visible, but might show up when you open and close an internal crack by moving the lead about.
The carbon inside the pickup can crack.
Is the base of the lead (where it screws in to to pickup) in good contact with the carbon block just below the threaded section?
There are a couple of things you can do to check.
Put the bike somewhere dark and either start it or kick it over. Watch around the pickup. You might see spark leakage.
If you have a multimeter, and the pickup out of the bike, you could test for continuity - or at least resistance. I'd try whilst moving the lead about, then between the carbon ends. A bit of Jiggling should show up any problems.
Nice looking bike by the way.
Brenton
'51,'56 Squares, '48 VH, '27 Model C, R67/2, Mk IV Le Mans, '06 Super Duke and Ariel projects.

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robjameson
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Postby robjameson » Sun Jul 29, 2012 5:42 pm

Thank you for the advise both.

As it turns out, it seems to be down to a bad earth between the mag and engine, even though the mag is earthed to the engine plates this doesn't seem to have been good enough, and running an earth to the barrel stud seems to have worked perfectly.

This has obviously perplexed me because no smoke escaped from the electrics so I thought they were okay!
Rob Jameson
AOMCC Member Number 4068
1957 Ariel VH
1956 Ariel KH (LARGE project!)

robin.parker
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Postby robin.parker » Mon Jul 30, 2012 5:37 pm

Aha, Don't be fooled Rob, High Tension smoke is an entirely different proposition, and obeys it's own peculiar set of rules. I'm presently looking for my college notes on the subject, when I find them I might be able to offer an explanation.


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