bad rotor after all these years

crassius

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Sep 30, 2012
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finally found a bad rotor on a motor that sat for 5 or 6 years - replaced rotor and all was well

motor ran before sitting all those years so sitting may be a cause of that weakness over time
 

2door

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Sep 15, 2008
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Littleton, Colorado
We're talking 'magnet', right? I call it a 'rotor' too but not sure everyone else does.

The magnet is the rotor, the magneto coil/frame is the 'stator'. At least if you use proper terminology.

Easy way to remember between the two. The 'rotor' rotates. The 'stator' stays where it is.

Tom
 

crassius

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Sep 30, 2012
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yeah, it got so weak that it wouldn't stick to my toolbox on one side

got a lot of them around here, so may start storing them as a circular daisy chain to keep them all fresh

somewhere packed away I have a magentizer to restore magnets in 1950s BHT magnetos, but not wanting to dig it out
 

allen standley

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Oct 22, 2011
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Bangor, Maine
What would symptoms be for a bad rotor? Weak little spark? Hard Start? I got a bike that simply falls all over itself at the top end. Could a weak rotor do that? Got an NT on it. Tweaked and fussed and messed with it all last year. I run a pocket bike exp chamber exhaust, I stuffed a male battery terminal cleaner into the end for positive back pressure. It Does run better under a load but still seems to fall flat when I wind it up on level ground. Hmm.. Food for thought. Thanks Crassius.
 

crassius

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Sep 30, 2012
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a weak rotor has a weak spark at low speeds - expansion chambers can make more power, but it happens only at certain speeds - the reflected wave always takes same time to reach cylinder, so only scavenges at the RPM that has that amount of time between firings