OEM Gear doesn't fit. Is this common,or is there a trick?

I am repairing my son's '07 450F,and replacing a couple of gears. I am trying to fit the 5'th gear wheel(new) onto the shaft. It meshes w/ the 3'rd gear wheel(also new).

The gear only slides on so far,then it will bind.the old gears work fine,so I don't think it is the shaft.Is there some trick I am missing?Perhaps use lapping compound? Otherwise,I am going to send it back,and have to wait another week or 2 for a replacement.

I've been out in the garage for the past 2 hrs using lapping compound.First 150 grit, then 400 grit. Now everything seems to be working great.Just don't know why I should have to do this using OEM parts.

Don't you mean the 5th and 3rd pinions? The gears on the main shaft?

It's not normal. The gear is a 2S2-17151-00-00, correct?

No Gray, it's called the 5'th wheel gear p/n-2S2-17251-00-00.

They are on the other shaft that holds the countershaft sprocket. I am going to go ahead w/ the re-assymby,as it seems to be sliding back & forth easily now. I guess that there was a burr or something that I could not visably see.

Then you're replacing the 5th wheel because you had a problem with third or first gear skipping, or just because you found it worn?

My son was on an MX track.After landing off of a jump,he said it just locked-up.I saw that the shift lever was bent down,and cracked.I think he landed with his big 'ol foot standing on the lever (even though he said he didn't).He was probably in 3'rd when he landed. I found one of the cogs broken off.The 5'th wheel and shift fork had wear marks as well.

Ah. I wondered because I heard of someone replacing that gear to solve a problem with 5th skipping, and that, of course wasn't going to help him.

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