Rust on flywheel = no spark?

So Im tearing down this 86 or 88 125 I bought (thats up in the air right now :) ) and I'm tearing it down to correct some issues. Right now I'm chasing a no spark issue. After pulling the ignition cover, I see what I have attached in the image. Would flywheel rust cause a no spark condition?





Generally speaking, no.  Rust on the flywheel won't cause a no-spark problem.


However, what caused the rust (excess moisture) could potentially soak into the windings of the stator and lead to a few wraps shorting out.  Once that happens, then you could easily have a loss of spark.  The flywheel (rotor) is just some permanent magnets that create current flow in the stator (coils behind the flywheel) when it spins.  The rust on the outer part of the rotor won't affect the magnetic field.


The best way of testing electrical components is to swap a known good part in and see if you get spark.  For my money, I would look to the CDI, ignition coil, and spark plug boot first.

Yeah I gotta get that freaking flywheel off. I don't have a 27 mm puller for this thing. I do have a 3 jawed pulled but I definitely don't want to break the flywheel. That nut is on there good too due to the rust. Any tips on removal? I have the head stripped down to the piston. How can I keep the crank from moving? I thought about a 2x4 between the rod and the head but I'm afraid I'll snap the rod.

If you don't have a clutch basket wrench, you can wedge a piece of wood (I have also used a small piece of aluminum) between the primary drive gear and the clutch basket.  That will lock up the crank from the clutch side.


Give the flywheel nut a good blast of liquid wrench or other penetrating oil and let it sit over night.  But, you will definitely need a proper flywheel puller to get it off.  You don't want to use the three jaw, and you don't want to use much heat either.  I mangled a flywheel on a CR80 years ago trying to get it off without the proper puller.  Finally ponied up for the puller, and it all came off with literally no fuss compared to how I was trying.

Edited by USED YZ426F

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