Wednesday, May 5, 2010

The Flywheel is at the Shop

That sounds like a pass code phrase you'd hear in a bad spy movie. Anyway, the flywheel is in the shop, and they are going to put it on the machine in the next couple days, to test it and balance it.

While I was there the machinist said something that's got me a bit worried. He looked at the flywheel and said that he'd be surprised if it was out of balance because it was a "zero balance" flywheel. He asked what it's bolted to. I explained how the taper-lock hub mounts to the motor and the flywheel to the hub. He asked if there was any chance the hub was out of balance.

The truth is I have no idea if the hub is in balance. I mentioned yesterday that the motor did vibrate a bit once I'd removed the flywheel. Could that have been caused by the hub being out of balance? I just don't know. There was definitely an improvement in balance when I removed the flywheel. That stands to reason that it was part of the problem.

Let's suppose the hub is out of balance. The question becomes would the flywheel being bolted to the assembly exacerbate the small wobble I saw once the flywheel was removed? It stands to reason that if that were the case, having the clutch plate and disk bolted to the assembly would make it even worse. That's not what I saw. There was no appreciable change in wobble between having the clutch plate mounted and not.

If they find the flywheel is balanced and the problem becomes the taper-lock hub, I'm not quite sure what I need to do to get it fixed.

UPDATE: The shop just called to tell me that the flywheel was indeed out of balance. 6 grams to be precise. I should have it back this afternoon and I can mount it up and see what we get. Stay tuned.


Gam0ra said...

Any balance or perpendicularity problem will be exaggerated more the further the object extends out from the center. So maybe the hub is the problem, but the flywheel being attached makes it that much more obvious by being a longer arm for the motion to move.

That doesn't explain the clutch assembly failing to make it worse though. If the clutch assembly doesn't extend it out from the center (i.e. has the same or smaller diameter) then I don't think it would make things worse to attach it.

Hmmm...there's all kinds of confounding issues there. I would certainly stablize the engine somewhere you can do measurements, strip all the external extras off and do the best you can to determine if the engine wobbles, then build out from there.

There are a couple of different ways you could check for wobble with a simple laser pointer.

Tim Catellier said...

Agreed. I would think that adding the clutch assembly to the flywheel would make a difference. Even though it doesn't extend beyond the radius of the flywheel, it does add mass.

I'm not certain thought. However, I should know more in a few hours when I get the balanced flywheel back :)

Gam0ra said...

I haven't had an engine apart in over 20 years...the clutch assembly bolts directly to the flywheel right?

Is there any way the hub isn't mounted exactly concentric to the shaft? A small amount of variation there is going to cause a big difference.

Tim Catellier said...

The clutch plate bolts directly to the flywheel, holding the clutch disk between it and the flywheel. If it's balanced, it would simply add mass to the flywheel assembly as a whole. It wouldn't add more to the heavy side than the light side. So I don't know if that would manifest as more wobble, or show now change.

The nice thing about those hubs is that there's really no way to mount it off center. There is, however a possibility that it's off balance. But they're made for this type of work, where balance is critical. So it should be balanced. But then I would have said the same thing about the flywheel.