Here's what I know about Roberts R2R capstan speed sleeves. I don't know about your 800X, but I have two Roberts 720's. They have a 2 speed switch, high and low, as it appears your 800X does. No capstan sleeve gives you 1 7/8 IPS and 3 1/4 IPS. Install the capstan sleeve, and you get 3 1/4 and 7 1/2 IPS. The 2 720's I have are exactly alike except for their capstan sleeves, and the capstans. One takes a sleeve with a notch at the back that locks the sleeve so it will not spin on the capstan. The other one has the capstan threaded on the end, takes a shorter sleeve with no notch, and a knurled nut screws on the capstan to keep the sleeve spinning with the capstan. I also have the optional larger capstan sleeve that fits the one that needs a nut on the capstan to hold it. It has no notch. This gives you 7 1/2 IPS, and 15 IPS. With the kit, comes a smaller diameter pinch roller to make up for the larger diameter sleeve. I wonder if your 7 1/2 speed issue could be caused by the wrong diameter pinch roller with the sleeve you are using. I don't know if these 720 parts are the same as your 800X, but if you need measurements of sleeves or pinch rollers, let me know. I was a kid with my Dad in 1964 when he bought one of these 720's. I struggle to keep that single motor, single head machine working, but I love the 6 watt tube amps in it. Hope this helps, and doesn't confuse.
