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Countershaft leakage

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Bike is a 2007 525 EXC. No leakage at countershaft prior to new sprocket. Bought a new Tag Metals countershaft sprocket. Now there is leakage. I replaced the bolt, spring washer, seal, o-ring, and spacer. Still leakage. With the sprocket off the shaft, I noticed that there is a small amount of in and out movement of the countershaft. About 1/64" I'd guess. With the sprocket installed the amount of play seems to improve slightly. Still some play.

Question: Is play at the countershaft normal when the sprocket is off the bike? Will an oem sprocket take up the play?

Edited by Dustbuster

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The problem very likely is that the aftermarket sprocket is too thin and therefore the o-ring is not sealing against the bottom of the spacer. Mike the stock sprocket and OEM sprocket to verify. I recommend using the OEM sprocket.

P.S. A little play is normal.

Edited by Chas_M
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Thanks. My local KTM shop has an oem sprocket. I will bring the Tag sprocket to verify. Good to know about the countershaft play. That's a huge relief.

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Yes, prob the sprocket is too thin. Always change the spring washer.

This is a fairly common problem. The stock O-ring on the RFS engine is 25.12mm X 1.78mm. You can find a 25mm x 2mm o-ring, I bought one on ebay for about 1$. It adds a little bit of thickness for a better fit. Still use a proper thickness sprocket.

Edited by trooper8

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For a slightly thicker O-ring, some of us use the KTM O-ring for 2 strokes which is the same diameter but a little thicker.

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I have a new 2012 exc 500,an i too have a little leak by sprocket,it is a new renthal.I did measure it an it seems to be the same size as stock or a little thicker,but i have to ask.Shouldt i have the sprocket wit smooth side face out or in,cause the stock sprocket has the smooth side facing out......wit the collar facing in..if that makes any sence?????

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I've heard a few different people with small leaks from countershaft sprocket including myself, not sure about your case but for me it only leaks when i let it sit on the kickstand, but not very much at all, when i leave it on the bike stand no matter how long i do not leak what so ever.

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another thing to check is your chain tension, if its too tightg it will cause the seal to start leaking early.

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KTM's aren't fond of aftermarket sprockets. Either beef up your o-ring like people have stated, or stick with KTM parts for the front drive.

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