electrics

[fallenmikethebike]

O/K the sh!!tty stick is firmly in my hands at the moment , i went out to put a few miles on the the top end after the rebuild .
Bimbling along nicely , when bwoooar , nothing , but not as i feared a repeat of Scrubs troubles , no , just no electrics , not even enough to light up the neutral , so having got back home i have taken the mag cover off, and it smells quite burnt in there , what or where can i test to confirm that the mag is toast .
their is a tiny voltage on the two terminals that go to pick ups , there doesn't seem to be any voltage at the main 5 amp,fuse[which i have tested ] i have taken out the plug ,and can spin the the rear wheel in first gear to turn the engine , but no reading or power is evident .
Is it still west country windings that are the top dogs for rewinds .
thanks Mike

[Furnuts]

magneto's usually have 2 windings, a primary (thicker wire) and a secondary (thinner wire but many more turns)

the primary should measure Very low like < a few ohms

the secondary should measure very high like > a few thousand ohms (depends on application) but not open

u can use a spark plug to test it, as a Voltage meter will usually get fried from high current produced by the mag.
connect the lead of the spark plug to it and then use a wire to connect the outer metal of the plug to the outer case of the mag (ground) and give it some turns, you should see a spark (you might have to turn out the lights to see it)

you also may have condensation in the mag

you can bake it in the oven on about 250 degrees Fahrenheit for an hour or so and let it cool off (let cool in the oven)
then test it again make sure no plastic parts go in the oven with it as you dont want to melt them or start a fire (i havent looked at my mag so u may not be able to bake it, use common sense)

ill take a gander at mine a bit later and let u know what it should read.

[fallenmikethebike]

Thanks Furnuts , i think it has more or less confirmed the fault as it has now started to work again , intermittent, the mag sounds like the culprit , but while the body work was off recently i went through all the connector blocks to check for muck ect , should have left well enough alone .
I will take out the bike again and see if the same problem recurs ,when its got hot , which would indicate that the windings are fecked .
regards Mike

[Furnuts]

what does a mag cost for a crm anyway? ... on your side of the pond that is...

cheaper to buy new or get rewound?

[chris356]

i have a good secondhand one of mk2 £15 (thats what i paid for it) plus postage if that helps & nowing my luck if i sell it mine will fick up while out in middle of nowhere thanks chris

[fallenmikethebike]

So now the quandary is ,run with it and take a chance , or just go for the rewind , reason being ,i have just been out again and put 15 miles of mixed running on it , and it never missed a beat .
i stopped it a few times and it burst back into life straight away .
Well ,i will just have to go out again tomorrow .

[kernow krusty]

Hi Mike,
Before ripping it apart, just try a hot air paint stripper gun on the windings...that will allow you to warm it up whilst stationary, with the engine running..
You could even plug your multimeter in and watch the volts to see if they vary as you warm the windings up. Dodgy windings may break down as the heat rises..and the volts would drop away.
My Mk2 would generate up to 14.2v in neutral on the sidestand, with a few revs.
Dont go too mad with the heat gun, as they can generate quite a bit of heat.
Regards KK

[fallenmikethebike]

Thanks KK i will try and give that a go tomorrow .

[Furnuts]

if you get the condensation out (if that's the issue) then try and spray it with a lacquer after to seal it good (nail polish works well also) i have seen the guys at the Rewind shop do that when they didnt feel like winding a motor.

[fallenmikethebike]

The cheating barstewards, , but thanks for the tip anyway .

[Furnuts]

yeah, but all the equipment ive ever done mag work on or seen it done to was either the old tractor, or on the naval base... none of those things traveled far from the shop, so when they finally did go it was a simple fix as they werent capable of traveling down the highway and stranding us on the other side of town

[fallenmikethebike]

Well , i went out again today and can report that the bike ran absolutely fine .I put about 60 mls on it today , again of mixed lanes and roads and no hint of any problems , so , on balance , and hoping i will not regret the decision next week i will run with it like it is .
KK you mentioned putting a test on the electrics whilst the engine was running ,is it the two terminals above the mag that i apply the probes too ? or do i need to break into the loom at some point ?
Regards Mike .