I've been struggling with a nagging vibration ever since I replaced bearings and belts in my old belt drive Grizzly lathe. Nothing I tried would make it go away, and it was having an impact on my surface finish. I also suspected that the new spindle belt was mis-marked, all the tension adjustment I had wasn't enough to get the belt very tight.
Well, I finally had enough, but I didn't really feel like pulling the spindle again to try another belt. So, I ordered enough of the Fenner Power Twist link belt from McMaster-Carr to replace both belts on my machine. What a difference! Not only did it eliminate virtually all the vibration, it also runs much quieter, and there's no squeal when I start it up at top speed. I also think it's running a little bit faster. Maybe the new belts are running higher in the pulleys?
Also, that spindle belt I was questioning? I had to cut it to remove it, same as the original belt, which I still have on hand. The brand new belt, with the same B33 marking on it, was a good 3" longer than the old, worn, stretched belt. No wonder I couldn't get it tensioned properly! So much for "industry standards", guess I won't be relying on belt numbers in the future.
Not sure why I put this off so long, I've used these belts before and been very pleased with them. My only concern was/is running them in reverse, but the only time I really need to do that is if I'm doing metric threading, and that will be at very low speeds anyway, so I'm not going to worry about it.
Anyway, just thought I'd pass this on for any of you that might still be on the fence about trying these. I'll admit, I haven't tried turning anything yet, but I'll be heading out to the shop soon, if my surface finish doesn't show a marked improvement, I'll let ya'll know. Later.