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Gearbox problems - 4th gear started knocking

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Hello!

Crashed my KLX yesterday, a really small crash from low speed. Didn't see any external damage by quick inspection.

On the road on my way home I noticed a strange knocking sound coming from the left side of the engine. Thought it must be the chain, but went through gears and noticed it did it only on 4th. Washing all the mud off the front sprocket and chain didn't change anything, still knocking on fourth. No grinding, just a pretty loud consistent metallic clanking. I didn't dare to use the 4th anymore on my way home, but it seemed everything worked ok, gears change normally and didn't notice any skipping, just the sound.

 

Why would this happen? I think I was on 2nd when crashing. I have never heard anybody having gearbox problems with this bike. Shouldn't these be built like tanks downstairs? Don't think I'm in the mood of splitting the case right now just to check. I'll have to recheck the chain slapping, but I'm pretty sure it's not that. Very different sound.

Any thoughts?

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Does it knock throughout the full rpm range. I will get a knock from the bottom of 4th or 5th gear if i am lugging the motor when i should be in 2nd or 3rd if that makes sense. Only 4th? Seems odd.

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Does it knock throughout the full rpm range. I will get a knock from the bottom of 4th or 5th gear if i am lugging the motor when i should be in 2nd or 3rd if that makes sense. Only 4th? Seems odd.

 

Yes I think it does. Haven't had the balls to rev it much on 4th though. Same knocking on engine braking too. Could it be bent or loose shifter shaft or something related under the clutch or should I prepare for case splitting?

 

Found this topic

http://www.thumpertalk.com/topic/1051885-2013-fourth-gear-eating-machine/

Anyone knows more about that case?

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These bikes make a lot of drive chain noise. Try tightening the chain a little tighter than u normally would and see if the noise changes at all. The transmissions are pretty tough on these bikes.

Good luck

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Took out the clutch, shifter mechanism works as designed.

Turning the transmission shaft makes a click once in a revolution on 4th gear. Seems that a tooth has lost it's tip and causes the small skipping as the gears "jump" from tooth to tooth.

Guess I got really unlucky. The shifter pedal must have had just the correct type of hit to cause this.

 

Suggestions what to replace when splitting the case in addition to a forged piston? Bike has about 100 very soft hours. No racing, no hitting rev limiter, just some slow newbie trails riding and dualsporting with tall gearing. For example the clutch plates look just like new. Guess it would be smart to replace the bearings while there. What about camchain at these hours? What else?

 

Thanks

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Have you tried Wossner forged pistons from Germany? Thinkin of ordering a KXF Wossner, maybe it will fit a KLX also.

The same shop sells KXF full gasket sets, do they fit a KLX?

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Found this inside:

WP_20140625_021_720.jpg

 

 

The piston had also touched something:WP_20140625_009_720.jpg

 

 

...something like the crank probably when started for the very first time at the factory:WP_20140625_010_720.jpg

 

 

Piston pin was pretty badly worn, but generally the motor was in very good condition (maybe the pin had suffered a bit due to the crank contact). Two transmission bearings were toast due to the metal shavings from the broken gears. Threw in also new main bearings (although the old ones were in great shape) and a Wiseco piston. Even valve clearances were in spec after 100 hours on the motor. Think I don't need to tell that also silicone worms were found.

 

Now she's rockin n' rollin' again!

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