Combines rotor rumble

What type grass are you cuttingIJ Some varieties have a tendency to roll into clumps in the front cone, and likely require the straight bars to break up these bunches. If not, the helical arrangement of the spiral bars may carry these clumps to the rear too quickly, and likely would increase rotor rumble at the point where the rows of helical rotor bars transition back to the straight bars_strippers. Which strippers are you using on the rear of the rotorIJ Straight strippers will provide a smoother transition since they don't have the tendency to fight the vanes as do sawtooth strippers. Also, if you have the small angle kicker installed at the rear of the strippers, these will catch stems, as well, since they are slightly taller than the strippers themselves -- we often see this in bean vines. Hope this is clear. email if you'd like.

Installing Marlin elephant ears and wear bars has been know to take out the rumble.

We combine tall fescue grass. We had smooth bars on the back of the rotor. last year we installed a set of disrupters and rice bars in place of the smooth bars. We still get rotor rumble

Do you see any wrapping on the front rotor bearingIJ If so, it may be that your impellers are worn, or that the vanes in the front cone may need replacement. Where are your vane settings over the concaves and grates. Are they in good condition (about 1" tall)IJ Any chance one may be folded overIJ Is stem residue in good sized pieces or nearly whole coming out the rotor discharge, or is it torn up into small piecesIJ Are you using keystock gratesIJ Are you getting good separation, or do you see some rotor lossIJ Does the machine do OK in other cropsIJ Sorry about all these questions.

You might consider replacing the rubber bushings in the spline drive on the rear of the rotor. Theory -- At that RPM range the inertia of the rotor is helping to carry thru and at the same time the gearbox is driving. At higher and lower RPMs the weight of the rotor resists the drive. The larger the rotor the lower the RPM this happens. '60 series appear to do this at about 450-600 RPM and larger rotors at atound 400 -500 RPM. Worn bushings will magnify the effect. Hope this is understandable.

For the degree of unbalance that is the critical speed of the rotor and yes it varies inversely with the diameter squared and mass of the rotor. To keep the vibration acceptable when you pass through the critical speed you must get it rebalanced. Suggest you replace all the rasps before rebalancing if not done recently. Any large rotating cylindrical object performs this way. I have worked on large steam turbines and yes they act the same way.

I guess I would take all bars off first, make sure it is clean and try it again and then maybe try adding some weight to the side that is light before pulling it, I have balance my own this way. And check the bushings they could be bad at the top end.