I am finishing up a retrofit of a Boss 3 with a variable speed head. Everything works well and I am pleased, but there is an intermittant high-pitched whine and grinding noise at certain speeds. This happens whether or not the machine is in the high or low range. There is no specific RPM at which it will occur although it is usually in the mid-range of the speed. When it happens it won't go away on its own, but I can make it go away by turning the spindle speed crank and raising or lowering the range. Any thoughts on the root cause?
Is it possibly the speed change plate? The plate that the chain attaches to at the top of the head (inside). That is the only area I can think of that would create a grinding noise. I will have to assume that the rest of the vari-drive is in good shape. The bushings in the pulleys are good, the bearings are good, and the belts are good.
I have seen the bearing in the bottom front vari-disc start chewing through the varidisc. Enough of that and you will get non-standard noises.
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