LOOSE SPROCKET BOLTS: MR. KNOW-IT-ALL

Dear Mr. Know-It-All,
I’ve been an off-road enduro guy for many moons and have recently purchased a nice used KTM 400. It makes good power for me. The brakes are strong, and the suspension is just fine for my riding. My question concerns the rear sprocket. The bolts keep coming loose. I have Loctited them. This failed, and then I put on lock nuts. Again, failure. One ride and they loosen up again. Please help
“NorCal Fran”
via [email protected]

Well, Fran, from your query, I believe that this is most likely the first KTM you have owned. The PDS rear shock system used on the machine is linkless and requires more chain slack than a machine equipped with rear shock linkage. When the machine is ridden with an improperly adjusted chain (meaning not enough slack), the chain tightens when the suspension travels through its arc. When all of the chain freedom is used up, the rear wheel gets put under a tremendous amount of pressure in an attempt to let the suspension finish its job. With a bow-string-tight chain, there are only two ways for the energy to get released. The rear sprocket gets yanked so hard that the bolts oval out of the rear hub, or the countershaft sprocket gets pulled back and can actually break the cases.

Unfortunately, once the hub’s sprocket holes oval, the hub is worthless. My rule of thumb is three fingers under the chain at the back of the chain slapper (see photo). Another good rule to follow is that a chain that is too loose is far better than a chain that is too tight—no matter the machine.

If you don’t mind displaying your ignorance for the world to see, who are we to deny the opportunity? Send evidence of your failures to
[email protected] or Mr. Know-It-All
Dirt Bike, P.O. Box 957, Valencia, CA 91380-9057

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