Major flywheel issue

When I took my flywheel off my Grande for the first time (last week) I discovered that the woodruff key holding it to the crankshaft had been sheared right in half. I figured it was old and worn so I put a new one in. When I opened it again yesterday to replace wires on the stator plate (electrical issues) I discovered it had been sheared in half again!

The bike only ran a total of 5 minutes before I opened it again, but I spent a lot more time than that turning the engine over by hand and riding the bike down the driveway to check for spark or see if the engine would start.

As for damage that I can identify, there seems to be some scoring of the flywheel where bits of metal were ground up as the crankshaft spun, and a little "notching" where the flywheel should push up against the woodruff key. It's not much though, the woodruff key still pushes up against the flywheel solid.

Does anyone know if I'm doing something wrong, or why it might be breaking?

Thanks,

Hank

Re: Major flywheel issue

See Ya Moped Army /

Is the corresponding notch in the flywheel stripped? If so, you need a new flywheel. If the notch in the crank is stripped, you need a new main crank.

Re: Major flywheel issue

Hanky B /
hank OP

The notch in the crank is pristine. THe notch in the flywheel has been widened a bit, but it isn't stripped. You can see a dent in the notch where the woodruff key has been pushing against the flywheel. Does that mean I need a new flywheel?

Re: Major flywheel issue

See Ya Moped Army /

If the flywheel is spinning, you need either a new woodruff key or a new flywheel.

Re: Major flywheel issue

Jason Luther /

when the key is in there is there any play, ie can you wiggle the flywheel _at all_ ? is the flywheel dragging on one of the coils or something, like when it gets warm and expands, and then seizing and shearing off the key?

Re: Major flywheel issue

i'm guessing it's a tapered fit on a tapered shaft?

If so, the taper is what keeps the wheel from spinnng on the shaft, not the key or some mechanical fastener..

clean the taper and the wheel's inner taper. Make sure there's not the slightet dirt, bump or nick on either part.

Re: Major flywheel issue

Hanky B /
hank OP

mopedlar: I put a new one in after I found it sheared the first time, and it sheared it again. I'd put another new one in now but I'm afraid it'll just break again until I find the problem

Jason: When I put in a fresh key I didn't notice any play when I spun it by hand, but it may be different when the engine kicks in. Also I don't think it's dragging on a coil because the inside of the flywheel looks clean.

joew: That's interesting about the taper. Yes there is a taper and I did not check for cleanliness. I have a question though, what is the key for then, to keep the magnets aligned with something?

Thanks everyone for the help so far!

Hank

Re: Major flywheel issue

alignment, yup.

Re: Major flywheel issue

Hanky B /
hank OP

Ah, SHIT.

I went to go clean the tapers and I think I found the problem. The taper on the crankshaft is nice and smooth, but the taper on the flywheel is chewed up pretty good. Must be from when the woodruff key disintigrated the first time.

Looks like I gotta get me a new one unless anyone has a good idea on how to "fix" this one.

Thanks again.

Hank

Re: Major flywheel issue

The woodruff key disintegrated the first time because the taper lost it's grip for some reason. Then the taper got damaged when the wheel spun..

you dont need 100% surface contact between the taper and the wheel ..

File high spots down smooth, as carefully as possible, retaining as must of the original taper surface as possible.. You might salvage the crank.

new key

When you get around to fitting a new key, make sure there's no slop. (This has nothing to do with keeping the wheel from spinning. It's about alignment.) Raw key stock is available in lengths, from a good hardware store.

Cut / file a custom key to fit whatever gaps in the damaged slot you need to fill. Use a drop of Loctite to keep the key in the shaft slot.

Re: new key

Hanky B /
hank OP

Thanks Joew, I've already started the filing process. Should the flywheel stick tight to the crank when it's just set on there? Or does it not fully fit until it's tightened down on there somehow.

Also, I found that the coils DID in fact rub up against the edge of the flywheel. Is it ok to sand down the round part of those magnetic plates that get really close to the flywheel?

I think this may work yet!

Thanks,

Hank

Re: new key

if you ever owned a lathe with a morse tapered headstock, etc, you know that if the surfaces are perfect, the taper grabs with almost no applied pressure.. which is why it makes such a good, strong temporary joint for driven rotating parts.

air gap between the magnets and coil armatures should be something like 0.1 inch or less .. as close as possible without rubbing when parts expand with heat or whatever. (Closer means the coils experience a stronger magnetic field)

Sand, trim, cut or file whatever needs it..

Whatever you do, try and maintain the wheel's balance.

Re: new key

Jason Luther /

the coils should be adjustable. if not fill them and dont touch the flywheel

Re: new key

Hanky B /
hank OP

alright, it looks like I might need a new flywheel, it's just not going to grab as well as it needs to. Hopefully the crank is still fine, it looks pretty good, but there is a little scarring. The coils aren't adjustable enough, so I'm working on sanding them, but I won't touch the new flywheel if I get one.

Thanks for all this help and so quickly!

Hank

Re: new key

try this..

Machinists have a special bluing spray. You spray it on two parts, let it dry a few moments and then put the parts together. Then separate the parts.

Wherever the parts touched, the bluing sticks/rubs off and is removed. It's a method of highlighting any high spots on the mating surfaces.

Re: new key

Hanky B /
hank OP

Well, due to excessive gouging of the old flywheel, I got a new (used) one from zippy. The taper on the new flywheel looks great, but it still doesn't really GRAB the crank. I'm about to lose it. Hopefully I can file down anything that's keeping it from making great contact.

Do I want the surfaces to be perfectly smooth, or rough? should I use a certain grit sandpaper to make these guys stick?

If I need to buy a new crankshaft, I WILL cry.

Thanks again.

Hank

Re: new key

since friction is what holds the parts together, ideally you'd want perfectly smooth surfaces... smooth and polished. This maximizes contact area between two parts.

kinda like using slicks on a racecar (as long as the track is dry).

try some sort of "bluing". Use a felt pen on the crank's taper.. that might do it ..

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