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countershaft sprocket problems


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I have an 06 450F and I tried to replace the countershaft sprocket today. It was on ridiculously tight, which appears to be typical, so I gave up and went to the dealer to have them remove it. The nut came right off with no problem with an impact gun.

The trouble now is replacing it. When I put on the new sprocket and tighten it down it contacts the engine case ! I thought it was a bad fit of an aftermarket sprocket, so I tried the original again, and when mounted with the flat side in per the manual, tightened it up and it contacted the case too!

What could have changed the bike worked perfectly before this? I'm reusing the lock washer does this matter? As a side note - the output shaft collar the the sprocket seats against is flush with the engine case. Is this normal? If it stuck out it seems it would provide the required clearance between the sprocket and the engine case. There is very little (maybe a 1/16") lateral play in the output shaft and the shifting is fine so it does appear to be tranny related.

Anybody have any ideas.

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The collar is there. It sticks out about an 1/8" past the oil seal and the top of the collar is flush or even with the surrounding engine case. So when I tighten the sprocket against the collar it contacts both the collar and engine case. Is there a washer or spacer between the collar and sprocket that I may have lost? A 1/16th washer would do the trick. Or is it possible that the collar is pushed to far into the motor? I dont see how the collar would push inward as it bottoms against the bearing for the output shaft and the bearing has retainers and is made to be torqued to 93 ftlbs.

This really has me stumped as it should be an easy operation. Any ideas?

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I also had a problem in the past (in 06) where Sunstar had the wrong part number in their book and you were getting a KX250 sprocket and it didn't have the groove in the back.

You would then end up with the problem you're stating and nothing you could do about it. You need the sprocket with the groove in the back.

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Problem solved! Thanks for all the help. Turns out putting the sprocket on with the groove facing the case works like a charm. I wouldn't have been so stumped if the manual in Final Drive Section 11-7, didn't state;

"Engine Sprocket Installation

•Install the engine sprocket so that the flatten side faces

[A] inside." With pictures of the flat side facing the case.

Regardless it works now, thanks again for all the help.

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Watch out for putting your cams in as well. The picture is incorrect for the installation of your cams and the grooves to align with. The don't align perfectly flush across the top of the head like the picture shows.

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