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Tranny problem with my KTM 300 EXC 2005

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I had a problem in 2012 with my KTM 300 EXC 2005. I heard a ‘’crack’’ noise in the motor at the end of the season. I dont know if its my power valve failure (We noticed this when we opened the motor) or the tranny that cause this noice. I noticed right after this that my tranny didn’t work correctly. When I downshift from third gear to second gear or second gear to first gear… the shifter stay at the lowest level and didn’t get to their normal position and also didn’t downshift. Down shifting from another gear aren't a problem. So it cause me a lot of trouble in a single track ;(. So last winter, we opened the motor to change the piston and ring and open the tranny. We changed some parts but the problem stay the same. I also noticed that this problem get back when the engine begin to be hot… and not arrived often when the motor is cold
 
In fact any 2 stroke KTM 200-250-300 from 02-05 are pretty the same bike... only the piston change... so if you had this problem on your 200-250... it's the same as me...



This is the parts that I changed

#5-8-9-14 23-24-25 of this picture

http://www.cross-roads.fr/pieces_et_accessoires/vues_eclatees/motos_offroad/2007/505_sx_f_preseries/shifting_mechanism-10935.html
 
I need help… it’s a nightmare for me

Dirt372
Québec, Canada

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Curious.....  Did you ever figure out what the problem was?  

 

I have an '05 300 exc as well and had a somewhat similar issue.  I never heard a "crack" noise, but I lost my power band while riding.  Turns out, there is a pin that allows the power valve mechanism to swivel, which is prone to falling out.  When it falls out it ends up in your crank case.  I found it when I drained the oil and it was stuck to the magnetic oil plug.  Fortunately, there was no damage done when it fell out.  After 2 attempts to get it to stay put, I had to have it welded in place.  Just thought I would give you my experience.

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To fix this the pin must be welded as you found out. The pin does not fall into the crankcase, it goes into the gear box and clutch area. So, it could get in the gears or clutch gears and screw something up.

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