Sprocket won't stay put

[Wolfie]

I built a simple go kart but I can't keep the sprocket in place.

I align the sprocket with the teeth on the clutch above, then tighten down the sprocket very tightly and it is snug on the axel, put the chain on and it is nice and tight, and then after riding a very short distance, the sprocket shifts out of alignment and the chain comes off.

BTW, the clutch is nice and tight also.

After chain comes off, I check the sprocket and it is still very tight, it won't move when I tap it with a rubber mallet?!?

Obviously the sprocket is shifting. Just can't figure out how or why if it is very tight. Is it being shifted by the torque of the chain?

I ordered some locking collars to try keep the sprocket from shifting.

Any other ideas out there?

 

[Hellion]

Make sure the engine/engine shaft/sprocket is absolutely lined up and square with the axle and vice versa. If the engine is straight and the axle has any sort of cockeyed angle to it, the misaligned chain can "walk" it and the sprocket away. Could be other things as well.

Mark the sprocket's position on the axle with a Sharpie?

Got pics? You can post them directly to this thread.

 

[Wolfie]

Could be that the sprocket is bent and under torque it get's pulled out of position

 

[Denny]

My wives! Stop using their pictures!

 

[Hellion]

Could be that the sprocket is bent and under torque it get's pulled out of position

Could be. Easy to check the sprocket runout with the Eyeball, Mark I. Could also be a weak motor mount that flexes under load (when the clutch is engaged and the kart is moving) which can pull the sprocket laterally once it goes out of 'true'.

it won't move when I tap it with a rubber mallet?!?

Well a rubber mallet is pretty soft and much of the force applied ends up as bounce or rebound. Maybe a brass or plastic-tipped hammer? It's okay to use steel (ball peen hammer) as long as you can modulate your blows and aren't an 800lbs gorilla. You don't want to destroy the thing of course. I'd mark the sprocket with lines drawn on the axle.

Let's see some photos, they speak 1,000 words.

 

[Whitetrashrocker]

Could be a bent axle too.
Id check that before taking pent up aggression out on that poor sprocket.

Speaking of sprockets. How's the teeth look. Worn sprockets like to pitch chains.