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Quick motor question on my 2004 ktm 125

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Hi TT, I am rebuilding my uncles 2004 ktm 125. He has complained about lack of power, so we decided to overhaul the entire bike. We have decided to replace the crank and piston, bearings and gaskets. Stupid me failed to do a compression test before tearing down. I don't know what I was thinking. Is there anything I can check as I rebuild for why there could of been a loss of power. I plan of tearing apart and rebuilding the head as well. To give you an idea the motor was full of black oil, is there a way to check the cylinder, there doesn't look to have any scratches or major marks, when installing a new piston do you wipe gas on the piston to give it an amount of lubricant? Any help is appreciated. Thanks

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Offthechizzain,

 

I'm no expert, but I don't think you can do a compression test if you have already tore the bike down. What I would do is check to make sure that there are no deep grooves in the cylinder walls and that the gaskets were in good condition. Was the piston still in good condition?  Before installing the piston I usually lightly coat the cylinder wall, piston, rings, wrist pin and wrist pin bearing with premix oil and then wipe them down with cloth (lint free of course). I leave the bearing as is though, I don't wipe it off. Like I said I am no expert this is just what I have done with my past few rebuilds.Good luck!

 

-Bum

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Hi TT, I am rebuilding my uncles 2004 ktm 125. He has complained about lack of power, so we decided to overhaul the entire bike. We have decided to replace the crank and piston, bearings and gaskets. Stupid me failed to do a compression test before tearing down. I don't know what I was thinking. Is there anything I can check as I rebuild for why there could of been a loss of power. I plan of tearing apart and rebuilding the head as well. To give you an idea the motor was full of black oil, is there a way to check the cylinder, there doesn't look to have any scratches or major marks, when installing a new piston do you wipe gas on the piston to give it an amount of lubricant? Any help is appreciated. Thanks

 

Use two stroke oil as lube assembling the engine.

 

Measure the cylinder and piston and work out the clearance, also look at the rings to see if they are worn, compare specs to manual.

 

2 strokes build up carbon and oil, they need to be rebuilt and cleaned regularly if the oil isn't being burned.

 

There is a chance that the power valve was gummed up and not moving properly causing a loss of power. KTM refers to this part as the exhaust flap.

 

Assemble this as per manual.

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