Tight spot magneto drive chain

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jj.palmer
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Re: Tight spot magneto drive chain

Postby jj.palmer » Mon Dec 16, 2019 6:25 pm

Alan, have been awaiting your solution, I have a similar situation but not has severe, the sprocket with the uneven worn teeth had possibly been previously mounted on a shaft that was running out of true and thats how the teeth had became uneven.

Regards,
John P.

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alan.moore
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Re: Tight spot magneto drive chain

Postby alan.moore » Mon Dec 16, 2019 11:27 pm

John, I think that is the most likely reason
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Re: Tight spot magneto drive chain

Postby Ian.Taylor » Tue Dec 17, 2019 5:27 am

I never had a problem on my VHA but I did on my 31 VF.
Same issue a tight spot then a very loose spot.
New sprockets & chain ordered , installed and the same !
Upon further investigation I came to realize the mag when pulled back was slightly crooked.
I now make sure the mag is even with the platform when adjusted and no more issues.

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Re: Tight spot magneto drive chain

Postby jj.palmer » Tue Dec 17, 2019 12:10 pm

Ian, to ensure that the mag. sprocket/spindle is correctly positioned a tool can be made to lightly clamp the assembly square whilst also controlling the tensioning of the chain with a pusher block (the wooden block with the square headed alumi. screw), see attached.

Another thought why sprocket teeth become unevenly worn, could it be that the engine power stroke creates more pressure/wear between
the sprocket teeth and chain with the other 3 engine strokes basically free wheeling, this assumes that the power stroke and the same
sprocket teeth are synchronized ?

John P.
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Re: Tight spot magneto drive chain

Postby Ian.Taylor » Tue Dec 17, 2019 4:15 pm

John
Great idea Thanks for sharing

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Re: Tight spot magneto drive chain

Postby alan.moore » Tue Dec 17, 2019 6:05 pm

John,
I made a clamp and pusher block after you posted it some time ago and it works a treat. I have noticed that the 5mm thick rubber seal sold by Drags, which fits in a metal 'top hat', is very hard and cannot be compressed to any significant degree unlike the old felt washer. The same washer/top hat seal is usually supplied by tony cooper when he recons a Mag. The 'top hat' fits into the recess on the back of the timing case. The 5mm seal thickness appears to set the mag at the correct offset so the mag and Cam sprockets line up. Being 'solid' it makes getting the Magneto square to the timing case a lot easier than with the felt washer.

Regarding the chain and power strokes I noted that, when the engine was turned by one revolution, the chain ended up in three different positions, relative to the sprockets, as the engine was rotated each revolution. i.e it took 3 revolutions to get the chain back to the same position on the sprockets. So in theory that should even out any chain stretch.

Cheers
Alan
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