Have a R52 and just before finishing soybeans it got to where it would not keep the cylinder speed correct. Belt looks pretty good. Is there a spring inside the big cylinder pulley that turns rotor be broke ? Any ideas ?
Would it only do it under a heavy load or was it happening at random times with no rhyme or reason? Do you have the gearbox on the high or the low side? You may be running out of power under certain conditions.
If the inside of the main shaft drive sheaves are absolutely dry (no oily film) the rotor hydraulic valve is leaking thru the "slower" poppet. The "faster" poppet is probably fine. Replace poppet and stem under the electric coil for "slower"