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Discussion Starter #1
I do most of my own basic wrenching, but after my wee-strom meets SUV incident in the fall, the bike was in at a shop in Barrie getting the plastics and other bits repaired. For convenience I asked them to do a spring tune up, check up and lube everything as well, as the crash had precluded me from doing it myself.

When I picked it up a couple of weeks ago they charged me for repairing a sheared flywheel key. As I said, I do most of my own work on the bike but there are places I haven't really looked into, and the flywheel is one of those places. A flywheel is one of those things that I know is in there, but only vaguely conceptually. I sometimes think I know what it does, but I probably wouldn't know one if I saw one. And when I mentioned this to my tech-savvy, former DL650 owner, riding friend, he was a little surprised, and suggested "keys" for flywheels are something you find on small, low rev engines, not on a larger higher-revving engine which would need something more robust. While I'm quite sure he'd know a flywheel if he saw one, I don't think he'd been into his DL's engine in that way while he owned it.

Wondering about this further, I opened up my electronic copy of the shop manual and searched "flywheel" and "flywheel key". Funny - "flywheel" doesn't generate a hit, leading me to suspect it is a term of art and there is a proper technical name for it that is used in the manual.

So, I still don't know and I'm wondering what it is, where it is, and whether the shop just charged me for something that's not really there.

This isn't critical, as they didn't charge me much for whatever they did or didn't do, I'd just like to know.
 

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FORUM GODFATHER.....R.I.P. PAT
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See page 3-33 in the service manual. What they are calling a flywheel is the magneto rotor. While it is located with a key, there is a tapered connection doing most of the holding. I don't see how the key could have sheared.
 

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What Kinda Bike Is That?
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See page 3-33 in the service manual. What they are calling a flywheel is the magneto rotor. While it is located with a key, the need for a rotor puller probably means there is a tapered connection doing most of the holding. I don't see how the key could have sheared.
Is it #8 in the diagram below?

 

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Discussion Starter #4
So the key is the little nub sticking up from the generator/magneto (they call it generator in my copy) rotor axle? Interesting. It doesn't seem particularly robust, but I'll otherwise take your word for it that it was odd to have sheared.

The comment from the service manager was that the sheared key would lead to a failure to spark - no ignition. I asked if that was something that could have happened in the relatively low impact crash. He didn't think so.

So I wonder if it happened some time ago, perhaps from a ham handed tech assembling the bike way back when, but the resultant lack of ignition it could have caused was avoided because the axle and rotor were otherwise mated.

Thanks Grey
 

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FORUM GODFATHER.....R.I.P. PAT
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#8 is it. It's really to locate the rotor position. Besides creating the charging current, the rotor signals the Hall effect crankshaft position sensor held in bracket #3 to determine the spark timing. If the key is sheared, chances are the timing would be off. I don't see how that could have happened due to a crash unless the magneto cover was broken. I think you would have known if the timing was off before the crash. What would they be doing in there anyway?
 

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What would they be doing in there anyway?
That's my question also. There's absolutely no part of a tune up procedure that would require pulling the rotor. Further, the key doesn't prevent any rotational movement once the rotor is installed. It is on there with a large amount of torque and the taper is what holds it on. The key is merely for alignment during installation.

Something is very fishy here. I'd be asking why they pulled the rotor in the first place.

Maybe they turn the engine with an impact wrench :mrgreen:
 

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The only explanation that makes sense to me is that during the valve check, they found that the rotor bolt (what you normally use to turn the engine during a valve check -- it's accessed by unscrewing that large plug in the stator cover) was loose. This could only have been caused by a factory error -- normally the bolt would be far too tight to start unscrewing when it's just used to turn the engine.

Instead of just slathering on some Loctite and zapping the bolt back in there with an impact as most would have done, they disassembled the rotor and replaced the key to ensure that everything was lined up all peachy-keen and would stay that way.

The only parts needed would be the stator cover gasket, the key, and a bit of Loctite.

Sounds like good, thoughtful service, actually. :hurray:
 

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Discussion Starter #8
Well, if they did it out of a screw up or trying to screw me over, it wasn't much of an effort, because they didn't charge me much for it. Rather than ordering the part they said they made a new one to fit.

The engine ran well pre-crash and pre-service, it runs well now. I will let it lie and go with the "good, thoughtful service".

Thanks, fellas.
 

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Odd scenario. I suppose that an improperly torqued arbor bolt could reduce the hold on the tapered shaft and allow some rotation to occur and the rotational inertia of the flywheel sheered the key as the accident stopped the rear wheel suddenly. ??
 

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If Sheared

Odd scenario. I suppose that an improperly torqued arbor bolt could reduce the hold on the tapered shaft and allow some rotation to occur and the rotational inertia of the flywheel sheered the key as the accident stopped the rear wheel suddenly. ??
If this key was sheared you'd have damage on the crank shaft and/or the flywheel. I've never seen a key that was sheared do at least some damage. That being said, hopefully their home made replacement was dang near perfect.

Good luck
 

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I've repaired woodruff keys (half-moon shaped like #eight) that sheared without damaging the keyway. When a know-it-all jams something in the lathe the woodruff keys in the carriage may shear and prevent expensive damage. They are often soft steel. It is indeed a mystery how Don's sheared.

So why does this software put up a happy face when I want to put up the digit eight?
 

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Odd scenario. I suppose that an improperly torqued arbor bolt could reduce the hold on the tapered shaft and allow some rotation to occur and the rotational inertia of the flywheel sheered the key as the accident stopped the rear wheel suddenly. ??
I'm not so sure about this. Even when you remove the arbor bolt, you need an impact wrench on a rotor removal bolt to get that rotor off the tapered shaft.
 

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Discussion Starter #13
I was wrenching a little late late Saturday night (actually Sunday morning) and looked at this again. I get a sense the key is primarily for alignment purposes and the tapered shaft does the holding.

DRxDR - nothing about the crash caused the back wheel to stop any more suddenly than say locking the back brake. Actually, except for the part where I hit the side of the SUV at kind of an oblique angle, it was as fairly controlled push-pull stop, and the impact itself was not that hard.

I'll leave the whole thing as a mystery for now. Someday if I'm back in that shop I'll ask about it.
 

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That key breaks quite often on lawn tractors when owners hit the blade into something solid. Think of it like a fuse, stopping the sudden jolt from damaging the engine internals.

Now, as to why it would break on the bike. A sudden difference in the speeds of the engine and the wheel? Seems like the clutch would be the weakest link.
 

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FORUM GODFATHER.....R.I.P. PAT
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That key breaks quite often on lawn tractors when owners hit the blade into something solid.
That's a different story. It's a shear pin, not a Woodruff key. Outboard motors often have them too. As was mentioned, the key is only a locator. The taper is the holding mechanism. Shear pins are to prevent shaft damage and are not on tapered connections.
 
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