I wanted to add a few pics and a little more info in case anyone else was looking to substitute a 20 Series clutch on a Rupp.
I ended up taking a bit more than 1/8" off the clutch. Now that I have a close fit on the belt, the clutch engagement is much nicer. I wish it was at a lower RPM, but unless I substituted some lighter springs on the drive clutch, it wasn't going to happen any better than what I have it at now.
Here's a pic of machining the fixed portion of the clutch. You have to remove material from the hub. If you take more than 1/8" out, you'll have to trim the bushing a little as well. If not, it'll be fine.
Then you have to machine the button. Whatever you take off the hub, you have to remove from the button.
I ended up with a nice fit. No dragging. Engages as soon as I rev it.
The only down side so far is that it likes higher RPMs than I prefer to push my 45 year old HS40. I'm at 4500 RPMs top governed speed, and if I want to top out the clutch I need to go even faster. I'm not a top speed guy, so I don't care about it, but others are. If that's you, you're going to need some more RPMs to get top gear out of this drive clutch. I'm hoping as the springs wear that it will shift to a higher ratio easier.
While I'm on the topic, what is a safe top RPM for a 1970 HS40 with an aluminum flywheel? I'd prefer to stick with the stock 3600, but that's not going to happen with this clutch.
Joe
I ended up taking a bit more than 1/8" off the clutch. Now that I have a close fit on the belt, the clutch engagement is much nicer. I wish it was at a lower RPM, but unless I substituted some lighter springs on the drive clutch, it wasn't going to happen any better than what I have it at now.
Here's a pic of machining the fixed portion of the clutch. You have to remove material from the hub. If you take more than 1/8" out, you'll have to trim the bushing a little as well. If not, it'll be fine.
Then you have to machine the button. Whatever you take off the hub, you have to remove from the button.
I ended up with a nice fit. No dragging. Engages as soon as I rev it.
The only down side so far is that it likes higher RPMs than I prefer to push my 45 year old HS40. I'm at 4500 RPMs top governed speed, and if I want to top out the clutch I need to go even faster. I'm not a top speed guy, so I don't care about it, but others are. If that's you, you're going to need some more RPMs to get top gear out of this drive clutch. I'm hoping as the springs wear that it will shift to a higher ratio easier.
While I'm on the topic, what is a safe top RPM for a 1970 HS40 with an aluminum flywheel? I'd prefer to stick with the stock 3600, but that's not going to happen with this clutch.
Joe