Maintenance & Technical > KX250 / KX125
Main Bearing Repacement
mustangfury:
The piston clearance was almost perfect when i rebuilt the top end. It only has about 5 hours on it.
I was running a really lean fuel mixture because I was getting a lot of oil out the silencer. That solved the problem for a short time, then it started spitting oil out the back again and that is when i decided to break down the bottom end. The excess oil was not from a rich mixture but rather from the crank case. I had the bike jetted pretty lean with a 150 main and a 50 pilot. The manual calls for a 168 main and 52 pilot. I kept seeing oil so I kept going leaner, one size at a time. I have never seen a piston like this either, that is why i am wondering if it is due to the lean mixture I was running.
The piston currently in it is a standard size. Fortunately if the walls are worn I will be able to get a B, C, or D size.
Stang.
BDI:
I would say it was trying to seize up.
jonny500:
bdi, do you think the funny marks (the spirally curved marks) on the piston are due to vibration from the bottom end. the bore looks ok but should be measured i think
mustangfury:
oh sorry, I know what you are referring to now. The curling marks are an optical illusion from the way the camera picked up the lighting and the way the software compressed the full size picture. Click on the top picture of the three i posted earlier and zoom in to full resolution and you will see the ribs are running the way they should.
The marks i was wondering about were the two vertical lines on the intake side and the top wear on the exhaust side. the ribs are worn down a bit. BDI, do you think that the reason it was trying to sieze was from the lean(hot) mixture?
Here are two more pictures. They are a little darker but they don't show the ribs zoomed out.
sorry for the confusion. I guess you definitely haven't seen that before.
Stang
BDI:
--- Quote from: mustangfury on September 18, 2010, 11:58:29 AM ---oh sorry, I know what you are referring to now. The curling marks are an optical illusion from the way the camera picked up the lighting and the way the software compressed the full size picture. Click on the top picture of the three i posted earlier and zoom in to full resolution and you will see the ribs are running the way they should.
The marks i was wondering about were the two vertical lines on the intake side and the top wear on the exhaust side. the ribs are worn down a bit. BDI, do you think that the reason it was trying to sieze was from the lean(hot) mixture?
Here are two more pictures. They are a little darker but they don't show the ribs zoomed out.
sorry for the confusion. I guess you definitely haven't seen that before.
Stang
--- End quote ---
I would say yes.
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