Two weeks ago while using the lathe on my Shopsmith Mark V, I heard what sounded like the belt slipping. I’d also been having some problems cutting heavy stock on the bandsaw attachment, so I figured it was time to change the old belts.

I had replacement belts on-hand from Jacob Anderson Shopsmith Repair, so I started watching his excellent videos to figure out how to tear down the headstock and replace the belts, I quickly realized what my actual problem was: The floating motor sheave was stuck open, so when I turned the Shopsmith up to higher speeds, the motor sheave didn’t close in relation to control sheave opening up, so the drive belt had too much slack and wasn’t getting any traction. After roughly 45 years, the sheave got gummed up with old oil, grease, dirt, and sawdust.

The floating motor sheave is number 119 in the diagram:

Since I had to tear down half of the headstock to get the motor out to work on the sheave, I decided to go the rest of the way and replace the upper Poly V belt as well. The whole thing needed some serious cleaning, oiling, and greasing anyway. My model was made in the mid 1970s and I don’t think it had ever been completely taken apart. The putty was still in the quill set screw at the top of the case. I don’t expect that is the kind of thing you replace after scraping it out.

Again, Jacob Anderson’s videos were incredibly helpful in figuring out how everything comes apart and goes back together. If you need Shopsmith parts, buy them from him!

The whole process took longer than I expected. It took me about 20 hours over the course of four days to take it completely apart, clean it, oil the moving parts, grease the bearings, and get it all back together again. I’m including the time I spent watching videos and making various jigs to help me work on it.

A few tricky points:

1. Removing the spring on the motor sheave.

The spring needs to be compressed in order to remove the retaining ring, and that spring has considerable pressure and a washer with it. Using Jacob Anderson’s advice, I drilled a hole through a piece of plywood and carved a groove for the washer to set in, pushed the spring down, and held it in place with some quick clamps. The washer still shot across the room, and it was pretty tricky to get back together again, but I don’t see any way it could have been done without something like this board.

2. Unsticking the floating motor sheave.

This thing wouldn’t budge by hand. I had to use a piece of plywood underneath and one on top, hammering them together to force it open. Once open, I did a good cleaning to remove the grime, then polished the shaft to help the sheave move. It still doesn’t move as easily as the top one for me, but it does move.

3. Putting the idler shaft (number 105 in the diagram) and eccentric bushing (103) back in after replacing the Poly V belt (55). The old belt was stretched out, but this one was much tighter. I also frustrated myself by stupidly putting the idler shaft and eccentric bushing back in once before putting the Poly V belt in and had to take it back apart. What a pain.

4. Calibrating the speed control

First, none of my three sets of Allen wrenches were long enough to get to the tiny screw inside the speed control face in order to take it off. I had to go out and buy some longer ones.

Second, you can’t adjust the speed control without moving the drives, either with the motor or by hand. This is not easy, especially since you probably set the control sheave open as wide as it could go (high speed) when putting the belt on. In order to calibrate it, you need to close down the control sheave to get it back in Slow mode. You shouldn’t start the machine at a high speed anyway, so you have to do this all by hand. Adding the disc sander attachment helps quite a bit by giving you something to turn like a steering wheel.

5. Putting the switch back in

I wasn’t paying close attention to the orientation of the switch and had just assumed it was still in the Off position, despite lots of jostling, so I had to be careful when plugging it back in for the first time. Thankfully I got it right, but I think I might mark it or tape it next time.

Thankfully everything worked as expected when I put it back on the stand and flipped the switch. The difference is night and day. No more slipping belts or the drive stopping when cutting heavy stock on the bandsaw or shaping something on the lathe at high speed.

With regular oiling, I shouldn’t have the issue with the floating motor sheave locking up again. Fingers crossed.