B
Bogstandard
Guest
Now I have your attention, I am talking about flywheels, not body parts.
I was reading Chucks great post about his making of an open column twin, and Hilmar's comment about wobbly flywheels.
There are lots of ways of mounting flywheels, from keyed shafts, the way Chuck has done it with tapers (there are a few tapered methods) but the most general one, and the easiest to do is the humble grub screw stuck in from the side. But it is this grub screw method that causes the worst of the shakes.
If you can get the flywheel hole to be a 'wringing' fit on the shaft, there is usually no problems with runout, but with just a couple of thou clearance (like I usually get) the problem rears its ugly head as soon as we tighten up.
I have done one of my crappy sketches to show you what happens.
I have exaggerated it to show what happens when you use one grub screw from the side, it basically doubles the error on the fit of shaft to hole and 'kicks' the flywheel over to one side and gives you a pronounced side to side wobble.
The cure for this is fairly simple, stick another grub screw in the other side, as in the pic. You will still get wobble, but only up and down, which is much less noticeable and easily dressed up true, unlike with one grub screw, which can be dressed true, but move the grub screw and retighten and you will find the wobble comes back due to the unstable mounting contact points.
This is of course assuming your axle hole is concentric with the rest of the flywheel.
John
I was reading Chucks great post about his making of an open column twin, and Hilmar's comment about wobbly flywheels.
There are lots of ways of mounting flywheels, from keyed shafts, the way Chuck has done it with tapers (there are a few tapered methods) but the most general one, and the easiest to do is the humble grub screw stuck in from the side. But it is this grub screw method that causes the worst of the shakes.
If you can get the flywheel hole to be a 'wringing' fit on the shaft, there is usually no problems with runout, but with just a couple of thou clearance (like I usually get) the problem rears its ugly head as soon as we tighten up.
I have done one of my crappy sketches to show you what happens.
I have exaggerated it to show what happens when you use one grub screw from the side, it basically doubles the error on the fit of shaft to hole and 'kicks' the flywheel over to one side and gives you a pronounced side to side wobble.
The cure for this is fairly simple, stick another grub screw in the other side, as in the pic. You will still get wobble, but only up and down, which is much less noticeable and easily dressed up true, unlike with one grub screw, which can be dressed true, but move the grub screw and retighten and you will find the wobble comes back due to the unstable mounting contact points.
This is of course assuming your axle hole is concentric with the rest of the flywheel.
John