Magneto Axle Play

SkyenX

New Member
Joined
Sep 3, 2019
Messages
26
Hi all, I've been having some issues with the bike ever since moving to a different frame. The engine will rev up just fine all the way to 25mph, lots of acceleration, perfect fuel mix etc
But as soon as I try to go faster, the engine makes a really high pitched, pinging noise and bogs down as if it's losing spark. I've changed plugs and checked all connections but it still bogs down. (Oh also, it will sputter and cut out at idle sometimes, which confirms it's an electrical issue)
I noticed the Magneto has axial play, could this have anything to do with it? Video:
Thank you!
 


Greg58

Active Member
Joined
Jun 3, 2012
Messages
442
That a lot of movement, I have had one engine with that but it was not as bad. The only way I know to correct it is to add spacers on each side of the crankshaft, this would require a total breakdown of the engine. Maybe someone else has a better idea.
 

HumanPerson

Member
Joined
Oct 12, 2019
Messages
38
Is the small bevel gear on the other side fully seated and tightened down?
That is alot of play, are the bearing sets bad?
This is an old video but might be worth watching:
 

GreasyChris

Well-Known Member
Joined
Jan 3, 2019
Messages
789
That is excessive play for sure. Like @Greg58 said shims on the crank will fix it but requires a total teardown. Bad bearings as well will cause that. Again a teardown is required to fix it. How did it run on the old frame? The pinging noise sounds like preignition and could be related to the magnet but it could be your cdi is beginning to fail and changing the timing curve on you causing the preignition. You could try a different cdi before tearing down the engine
 

SkyenX

New Member
Joined
Sep 3, 2019
Messages
26
Thank you for all the advice, it's really helpful
The engine ran fantastic on the old frame, perfect performance up to 35-40mph
Did a compression test and it made 170psi which is stupid high. Dunno if the guys gauge was calibrated right but that could explain the pre-ignition. I'll try a new CDI first before tearing down the engine
 

SkyenX

New Member
Joined
Sep 3, 2019
Messages
26
Oh also! Could a dodgy killswitch cause this behaviour? Shorting out from the vibrations or something?
 

LewieBike

Active Member
Joined
May 21, 2014
Messages
685
You could try filing the magneto key and replacing the lost material on the oppoite side of the key slot with strips of shim metal, that would effectively reduce your ignition timing a couple degrees. You might also pull your head and see if your engine has built up a bit of carbon deposits on the piston top and inside of the head, that can cause pinging. IIRC 170 PSI seems a little high for a 6:1 compression ratio engine, so it's a good chance it's carbon. Carbon will also act as glowing hot spots, pre-igniting the fuel and causing pinging after the engine has warmed up.
 

SkyenX

New Member
Joined
Sep 3, 2019
Messages
26
Thanks Lewie,
I pulled the head when I changed frames and both the piston top and head were both completely black with carbon deposits. I assumed this was normal so I didn't clean it off because it would just come back again.
How should a perfect engine look on the inside? (FYI it has around 400 miles on it by now)
 
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