New rider. Busted my sprocket

[jaysun 10]

Just got back from the motocross track, where I busted my quad (2008 KFX 450). Keep in mind that these may be stupid questions. I'm new to riding and don't know anything about anything.

The chain was a little loose, I believe, and I probably should've tightened it (not that I know how to tighten a chain) but I'm not sure if that came into play here. I took a jump and didn't let off the throttle. I over-revved the engine and the rear sprocket snapped off while I was in the air.

It looks like there are 4 bolts that hold the sprocket on and it appears that those bolts have been completely sheared off (see pics below). If this is just a matter of replacing these bolts, that would be awesome. Are these bolts meant to shear under pressure (like the shear pin on a boat propeller)? Also, in the side that still has nuts, that bolt is pretty skinny. The corresponding hole on the sprocket is much larger. Are these some sort of specialty bolts?

Am I not even in the right ballpark with these issues? I seriously have no idea what I'm doing here.

I appreciate any help.

[wylde1 49]

I don't know what would have taken out all four bolts, but I would get a new sprocket. They are not that expensive.

[marioweldinginc 10]

Agreed ^ check the side play of the rear carrier also just spin the rear tires too. Any unusual play or noises might mean its time to replace bearings. Get a new front sprocket, rear sprocket and new chain so they can all wear together which makes em last longer. Make sure your chain slack is adjusted properly. You might of been on the tight side. When you jumped the weight of the swing arm and tires where carried by the sprocket.

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[BioWare 13]

Welcome

[quadnut20 75]

That is wierd ! It sheared all 4 bolts by the looks of that chain I`d get new sprockets and chain !!

Get a service manual for it !

[jaysun 10]

I did some more research (including getting a manual) and, apparently, this is a fairly common issue with Kawasakis. They use 8mm bolts, as opposed to 10mm bolts used my other manufacturers, like Honda. I read stories of people shearing all 4 bolts up to 4 or 5 times a year. Drilling out 10mm holes seems to resolve the issue every time, but I don't have the tools or the know-how to do that. I just went down to Lowes and picked up some new bolts and washers. Worked great. I'll be back on the track this weekend.

I think the chain and sprocket are still in decent condition. I took these photos right after coming back from the track, so everything was still really dirty. But what do I know? Not much.

[marioweldinginc 10]

Until you drill out the holes, i would try to find the strongest 8mm bolts possible. Not the ones from Home Depot or Lowes but from a bolt manufacturer. At the very least keep 4 sets of nuts/bolts with you incase it happens again. That way you will only be down for a few minutes instead of loading it on to the trailer. Make sure the chain slack is correct too.

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