magneto dead?

[mike667]

Hey guys
 got a question about my magneto - was out riding, thinking how beautiful the bike was running when she dropped dead in her tracks -  crapola - 1 mile push home, sweating and cursing. Turns out no sparky, which is what i suspected - here's the weird part - thinking the points closed etc i readjusted them and again no joy - when i put my little LED thing on it to ensure the points were opening - no matter what - even with the points obviously opened the led is still reading like they are closed (took points out  of the maggie the led changes with their opening etc)  - i'm thinking i must have a wire touching something and acting like the kill button is always on, but checking it out shows its only  working/conductive when the kill button depressed  - damn- the  lights all work fine, no blowing the fuse  -  can something in the magneto have dumped ? - its not that old of a rebuild on it, but we all known that a rebuild can go south too....

ok thanks as per usual
mike

[Beezageezauk]

Remove both pick-ups and try giving the slip-ring a good clean but not with the magneto rotating.  Then replace one pick-up and try it for a spark at the plug.  If this is ok, replace the second pick-up and try this one for a spark at the plug before you try firing up the engine.

No guarantee...but it sometimes works.

Beezageezauk.

[muskrat]

G'day Mike,
                   if everything else checks ok I would look at the insulating cups (not sure what their called) on the bearings. This was the cause of a similar problem I had years ago. Can't remember how I traced it but I think it was continuaty (not in my dick n harry) between armature and body.
Cheers

[mike667]

hey BeezaG and Muskrat
 thx for thoughts yes cleaning the slip-ring didn't work - thinking something must be bad in the maggie itself check all wires etc w/ stuff off another magneto bike- chap-ola- maybe only 50 miles on the rebuilt

 I have the original one that was in the bike and it worked OK that i was keepin for a spare, guess have to stick it back in and see if it fires up to confirm its the rebuilt mag  - wish it wasn't such a pain in the ass but what else would i be doing on a nice day besides riding and have some nice ales

argghhh

m

[Triton Thrasher]

when i put my little LED thing on it to ensure the points were opening - no matter what - even with the points obviously opened the led is still reading like they are closed

That's normal.

For it to stop so suddenly, I'd suspect the drive gear has stripped and it doesn't turn any more, or for some reason the points spring has started touching the cam ring, or something is open in the low tension circuit, such as where the wire goes onto the condenser.  Earth brush or brushes might be worth a check too.

[bikerjohndavies]

Hi Mike, I had a similar problem except that there was a bit of warning when it started to miss at low revs for a few miles before it died completely. It turned out to be the insulation washer between the bearing like muskrat suggested. This caused the armature bearing to short to the body and stop working. The mag had only done 900 miles since a rebuild so repaired under warranty.

[a10 gf]

To add to the confusion of possible causes... broken winding in armature winding? (or defective capacitor?)

If you have 2 mags, swap the armatures and see what happens. ps, no need to mount mag on the bike to test: with the drive gear on, turned quickly\firmly by hand with pickups removed, you should get a strong spark at the safety gap screws.

[Triton Thrasher]

Broken HT winding or failing condenser is usually a slow, horrible death!

[mike667]

thx for excellent suggestions guys - TT I looked at all bushes etc - they look fine, going to change it for old magneto this afternoon and hopefully she'll fire up - will at least tell me if mag is problem or not.

and i was thinking all my bikes were running perfect just before this - oh well will keep me from combining ebay looking for next project for at least a few days!

[mike667]

Success!
  old maggie back in and started 2nd kick - and all done under 1.5 hrs - damn i've impressed myself!

 thanks all as always - i'll let you know what the magneto guy says was at fault when returned

mike

[wilko]

I'm sure he'll say it needs a complete rebuild no matter what!!