Author Topic: have i fried my magneto ???. i hope not  (Read 1400 times)

Offline chicago

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have i fried my magneto ???. i hope not
« on: 18.09. 2012 00:15 »
hi fella's, just wanted some opinion's. pulled the top end off my bike, put it back together and now no spark at all. i didnt mess with any wirring, just took head barrels off. while i had the head off i started to kick the bike over and forgot to hold the engine cut out button down, i'm sure ive read on here that if the plugs are out of your bike and you kick the bike over you have to hold down the cut out button or you damage the magneto. so do you think i have knackered my magneto.
thanks in advance fella's, chicago
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Online Brian

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Re: have i fried my magneto ???. i hope not
« Reply #1 on: 18.09. 2012 00:58 »
No you havent damaged your magneto, disregard whatever you have read about that.

First I would disconnect the cut out wire at the magneto and see if you have spark. I assume you have new or good spark plugs. If still no spark run a piece of fine emery paper between the points and check their gap (.012").

Check the pick ups to see they are sitting correctly and you havent inadvertantly damaged a HT lead.

Let us know how you get on.
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Online groily

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Re: have i fried my magneto ???. i hope not
« Reply #2 on: 18.09. 2012 06:36 »
And here's why Brian's right to say you haven't damaged it, assuming you have your 'safety screws' fitted (which I'm sure you have): http://www.brightsparkmagnetos.com/faqs/FAQs%20about%20magnetos%20generally/What%20do%20safety%20screws%20do.htm
More than likely it's the kill button arrangement, dirty points or a lead/plug thing at the root of your problem like he said, unless there's been a series of unlikely coincidences and the thing chose this very moment to expire.
Cheers, Bill
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Offline fido

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Re: have i fried my magneto ???. i hope not
« Reply #3 on: 18.09. 2012 07:04 »
Usually the plug leads are different lengths so you can't get them mixed up but if incorrect fitting is physically possible on your bike you could check by swapping or the more scientific approach: Remove the front magneto pickup and turn over the engine until the metal segment in the slip ring is visible though the pickup hole. Now take off the valve covers to check which cylinder is on compression stroke. The front pickup lead should go to the cylinder on compression. You may need to use the pencil down a spark plug hole method to get top dead centre, as you no doubt did when you checked the valve clearances during re-assembly.
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Offline chicago

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Re: have i fried my magneto ???. i hope not
« Reply #4 on: 18.09. 2012 09:13 »
cheer's for the replies fella's.

upto now ive disconnected the cut out wire from the end of the magneto, ive took the pickups out and cleaned them, ive cleaned the slip ring, new plugs,
i didnt check the points as it was getting dark, not changed the ht wires, but will check them today.
the safety screws, where exactly would they be fitted, ive had a quick look but couldnt see any screws, i just hope it's got some fitted.

set tappet's, all a ok, i fitted the ht lead's with the pickup that sits closest to the cylinder/barrel going to the kick start side, im pretty sure thats the way it was fitted.
last night while trying to start it i did notice that the carb flooded due to a sticky float needle i think, and maybe petrol has got inside the points, would this cause the no spark ??.
cheer's for the advice guy's, at least ive got a few more idea's to try. just hope i can get it going without having to buy a magneto. i will let you all know the outcome, all the best fella's, chicago
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Offline chicago

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Re: have i fried my magneto ???. i hope not
« Reply #5 on: 18.09. 2012 11:45 »
UPDATE.......
you guy's have once again got me out of the dog doings, cleaned the points with a bit of fine wet n dry and sparking again, what a relief.
a really big thank you to all, if it wasnt for the collective knowledge and help of this forum and it's member's i think i would have give up on the bike age's ago.
i think what must have happened is with the bike being stuck in a damp garage without being run for the last month or so the points must have got damp and started to corrode a little.
i'm thinking maybe i should replace the points with some new one's.
once again fella's thank you so much. all the best, chicago.
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Offline fido

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Re: have i fried my magneto ???. i hope not
« Reply #6 on: 18.09. 2012 18:58 »
Only change the points if they are very worn or badly pitted. Remember that there are a lot of dodgy new parts available so new does not necessarily mean better. The points faces should be of an extremely hard material so it should take ages to polish out any pits. If the marks are easy to polish out you have rubbish points.
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Offline warmshed

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Re: have i fried my magneto ???. i hope not
« Reply #7 on: 19.09. 2012 09:12 »
If the points get damp its not unknown for the return spring, which runs close to the cam ring, to short out to the cam ring with a drop of moisture. this will stop any spark. As mentioned new points can be a problem, the contact faces often don't line up properly and the spring can be wrong and short out to the cam ring.
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Offline KenF

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Re: have i fried my magneto ???. i hope not
« Reply #8 on: 19.09. 2012 21:53 »
Good point, Warmshed. The shorting issue only applies to the later 'low-inertia' steel contact breaker assembly, where the moving point and the spring are live. In the earlier brass CB assembly, the moving point and spring are earthed, so if the spring touches the cam ring, it's no big deal electrically. But of course rubbing of spring and cam ring causes wear and breakage, so something to be avoided.

Ken. Brightspark Magnetos.
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Offline chicago

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Re: have i fried my magneto ???. i hope not
« Reply #9 on: 24.09. 2012 10:12 »
cheer's fella's.
did buy some points and they do look like nos but not sure as im no expert. i did have a quick look at the points that are fitted and they look ok with no pitting, i didnt go any further than just clean them with a bit of wet n dry, i did notice that it had the brass type backing plate.
all the best fella's, chicago
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Location: north west madchester.
Preferred location: somewhere warm and dry.
Bike: 1953 plunger Longstroke engine.