Loose flywheel - Pointy.

Hi peeps,

Bought a low mileage k4 two weeks ago, put about 100 miles on it and it breaks down turns out the magneto/flywheel has came loose, seems the only damage is a broken key and a few scratches on the shaft and magneto bore.

Do you recon its just bad luck and the bolt just worked loose or maybe its worn/faulty tapper on the shaft or magneto?

Also is it worth lapping the shaft and magneto tapper with grinding paste? is the fixing bolt supposed to have a washer? do i use thread lock on the bolt, and what do a torque it up to?

last question, where do i buy the shaft key and cover gasket from??

Thanks fellas..

[yorkie_chris]

Would recommend looking at the parts fiches on robinsons foundry website, also parts source there.
Also a service manual!

I wouldn't lapp that myself, I would stone out any big marks and blue it up to check fit.

Was it just spinning or banging around like a mad thing?

Ok thanks.

There was no major noise the engine just cut out i assume because the fuel injection was no longer getting any power from the magneto, i pressed the starter a couple of times after and it just spun the starter motor but didnt engage the engine.

took the cover off and found the bolt was loose and the shaft key had snapped. i just hope it was caused by a loose bolt and not a knackered taper.

cheers.

[yorkie_chris]

Aye it would have cut out because the signal to fire the sparks comes from there.

If the bolt was loose, this is your issue.
The keys are deliberately made softer than the other two parts so they self sacrifice if you have an issue of this sort.

Loose bolt means the flywheel will rotate clockwise and counterclockwise around the shaft. Whats the only thing stopping it? The key. This is why they're soft so they'll shear without damaging things.
Check things aren't out of shape before you bolt it all back together though, just for sanity.

C.

Well i would think the key's job is orientating the flywheel in the correct position on the shaft so the timing remains correct, its the taper that actually holds that heavy lump of metal on the shaft radially, and the bolt holds it Axially.

Anyway im just gonna clean the taper up and bolt the thing back on with a bit of blue loctite, torque it up and hope it dont happen again.

[squirrel_hunter]

I have had this once before on a Curvy. Short explanation, previous owner had a charging issue and replaced all of the charging system including the flywheel. When this was replaced the owner did the bolt up, but not tight enough. Bolt came loose, spun the flywheel. I replaced the flywheel and woodruff key and did the bolt up correctly 150nm off the top of my head. No Loctite required.

[yorkie_chris]

Originally Posted by jay998

Well i would think the key's job is orientating the flywheel in the correct position on the shaft so the timing remains correct, its the taper that actually holds that heavy lump of metal on the shaft radially, and the bolt holds it Axially.

Anyway im just gonna clean the taper up and bolt the thing back on with a bit of blue loctite, torque it up and hope it dont happen again.

Yeah correct it's friction does all the work really