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Hi;
Phonographs can be downright finiky. I've been repairing them for years and you never quite know what you're going to end up with until you're done. A speed issue like you've described can be caused by several things.
When the motor is disassembled, the upper and lower bearings need to be thoroughly cleaned of all residual grease. The motor shaft should be polished with a metal polish to remove any roughness or imperfections. When the motor is reassembled the upper and lower bearings must be perfectly in alignment with each other. Use a very light oil to lube. The slightest bit of friction can affect the speed. Give the reassembled motor a good spin by hand and it should spin for several seconds and slowly glide to a halt. If not, you need to adjust the position of the upper and/or lower motor bearings.
The idler wheel that sits between the motor shaft and the rim of the turntable platter must spin freely. Like the motor shaft, the shaft that the idler wheel spins on must be cleaned of any old lubricant and lubed with a very light oil. The idler must spin absolutely freely.
The turntable platter itself must be removed and it's bearing and shaft must be cleaned in a similar fashion to the motor and relubed. When reassembled it should spin freely.
After all of that if the speed is still off, you most likely have an issue with the motor itself. The only true way to check the speed is with a strobe disc and fluescent light or neon bulb.
Hope that helps.
Good luck.
Bob
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