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2-stroke Magnet Freeplay on 80cc Chinese Bicycle engine

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2-stroke Magnet Freeplay on 80cc Chinese Bicycle engine

Post by Fabian on Thu May 31 2012, 10:32


This video shows why some Chinese 2-stroke bicycle engines run better than others. It all depends where the magnet sits when the crankshaft nut is tightened on the magnet.




Last edited by Fabian on Tue Dec 25 2012, 07:43; edited 1 time in total

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Re: 2-stroke Magnet Freeplay on 80cc Chinese Bicycle engine

Post by kavid2012 on Thu Jun 14 2012, 01:18

are you saying the crankshaft can turn???
because magnet has key way and can't move as you know.

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Re: 2-stroke Magnet Freeplay on 80cc Chinese Bicycle engine

Post by kavid2012 on Thu Jun 14 2012, 01:23

and also do you know what is that thing he got in the video?
that round 360 degree paper thingy and how do you know where is the correct position for magnet?
do you know how to do it?
can you show me ?
thanks Very Happy

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Re: 2-stroke Magnet Freeplay on 80cc Chinese Bicycle engine

Post by Fabian on Thu Jun 14 2012, 02:06

Undo the nut holding magnet onto crankshaft - you will easily be able to feel the freeplay.

Where the magnet sits when tightening the nut will determine the ignition timing, based on how much freeplay there is between magnet and crankshaft and keyway; some engines have more and some engines have less.

The Jaguar CDI eliminates this issue because it has 4 selectable ignition curves.

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Re: 2-stroke Magnet Freeplay on 80cc Chinese Bicycle engine

Post by kavid2012 on Thu Jun 14 2012, 18:19

my crankshaft on the magneto side spins off the crank from turning the nut hard.
have you experienced this? do you think it's ok?

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Re: 2-stroke Magnet Freeplay on 80cc Chinese Bicycle engine

Post by Fabian on Thu Jun 14 2012, 18:32

It sounds like you have a stripped thread on the magneto side of the crankshaft.
Realistically in such a situation you have little choice but to replace the crankshaft.

I have seen this happen before.
At the end of the day, the magnet does not need high tension to hold it in place; only medium pressure is required combined with use of a medium strength thread locking compound like Loctite 243.

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Re: 2-stroke Magnet Freeplay on 80cc Chinese Bicycle engine

Post by kavid2012 on Thu Jun 14 2012, 21:19

i'm sorry it was clutch that was rotating lol Smile

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Re: 2-stroke Magnet Freeplay on 80cc Chinese Bicycle engine

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