How can a bad compensator cause a a grinding noise in the starter?

 

Not sure, but I'm on my 2nd starter and have had 2 OEM comps. and 2 SE comp. all under warranty, except the last starter and the last comp.(no warranty) The stealers installed one of the spring plates backward and destroyed the first SE comp. Now the stator is bad. coincidence, I don't think so. No warranty, so on my nickel. Yea, I could have made them replace the last comp., but I wouldn't take a bicycle there to have the chain looked at.

 

For all practical purposes, a compensator is a self centering spring cushion which is supposed to absorb and then return to the drive line over time abrupt impulses from the combustion strokes and compression strokes of the engine. When the fuel mixture fires there is a sudden pressure put on the piston that tries to speed up the crankshaft. The compensator slips a little to absorb the impulse and not transfer the sudden "jerk" into the drive line. As the piston nears the bottom of the stroke the energy absorbed by the spring is released back into the drive line again smoothing the flow of power. The reverse happens as the engine slows slightly on the compression stroke. The springs on the compensators installed on the first 96 ci engines were right at the limit for absorbing the energy for the engines and weakened with use. Some were not strong enough even when brand new.

As the spring weakened, the physical movement of the 2 pieces of the compensator became larger and larger until the stop was reached. The starter puts a very heavy impulse of torque into the clutch, primary chain and the sprocket side of the compensator. A weak compensator allows the starter, the clutch basket the chain and the comp sprocket to build inertia before the crank shaft begins to rotate. When the comp movement limit is hit, that shock load feeds back through the chain and clutch ring gear to slam the small rollers in the starter drive clutch. Because of the inertia previously described, several times the design load is put back into the starter drive clutch. Not many repetitions are needed to adequately wear or hammer the little rollers so they don't grab as they should and they slip and chatter before they finally rearrange themselves so they grab and turn the engine. That terrible grinding noise is very characteristic sprag clutch slippage. With a properly functioning compensator, the impulse of torque from the starter is smoothly absorbed by the spring in the compensator with no shock being fed back into the starter. The parts are not overloaded and last a long time.

The other possible starter grind is from not having the starter drive teeth properly engage the teeth on the clutch ring gear. The 2 sets of gear teeth grind against each other. Not many repetitions are needed to destroy either or both the starter drive and/or the ring gear. Unfortunately, the grinding noises sound quite similar so without a practiced ear one must either pull the starter to look at the drive teeth or the primary cover to look at both sets of teeth. If both sets of teeth are normal, the sprag clutch in the starter drive is on the way out. Hope this helps.

 

That is a damn good writeup..much appreciated..very well done.

 

i think that when the comp is even a little week and bottoms out when starting it will slowly beat the starter to death,the other major cause is a week battery or ground.