Piston Change pics

Casper250

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Dec 12, 2000
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#1
I picked up a new piston and rings for my bike. Bought it used so i wasn't sure how many hours where on it but it had at least 25 from me alone. I was VERY happy with how clean everything was. Little to no carbon build up in the pipe and the power valve was also VERY clean. 10 times better then what my kx250 looked like when I did a piston change on it.


Just some specs.
My first attempt at jetting so here is what I was running.
I was running 100 octain Coastal pump fuel.
Maxima Super M at 32:1.
45 pilot(stock)
380 main(stock)
2170 needle, second clip from top.

I believe that the main is running to lean still. If I went WOT at a low RPM the bike would just die, but if the RPMs were up it wouldn't happen.

As for the Super M, I like it. Everything had a nice coat of oil on it when I was taking the engine apart. The power valve was cleaner then anything I have ever experienced when rebuilding a bike. And when I spun the crank 180 degrees, the part of the crank that was at the bottom had a nice thick coat of oil meaning that there was a puddle at the bottom of the crank case.

The piston looks good to me. Some small signs of blow by. In the picture, it looks like there is a black spot at the top, that is just the lighting. The exhaust side is on the bottom. The actual color of the top is a couple shades lighter then what it looks like, again the lighting.
 

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Casper250

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#3
Oh yeah, BTW, does anyone has the torque specs for the cylender head and cylender for a 2001 CR125?
 
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#5
Isn't blow-by caused by excessive piston to inner cylinder wall clearance? How could you tell the small signs of blow-by by looking at the top of the piston.

BTW, I had my cyl. head off about 3 months ago and that's what my piston looked like. Nearly the exact same thing.
 
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#6
A poor ring seal is the most likely cause of blow by...But you've got the idea...Too much clearance between the cylinder and piston ring.
 

Casper250

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#7
I could tell the blow by from looking at the side of the piston, i have picutes of the side but they didn't come out good. You can tell there is blow by from the side of the piston having a brownish color past the piston ring. I'll see if I can take a better picture tonight.
 
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#9
I was running 98 octane unlead pump fuel
Castrol TTS 32:1.
35 pilot
400 main(cylinder modified by MXT in order to achieve more top end)
2168 needle, second clip from top
AS 1,5 out

With 2170 needle maybe you should rich your main a bit...
 

bedell99

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#10
I torque my head down to 20 ft-lbs of torque for the head bolts. That is usually the standard. The cylinder I can't get a torque wrench at, so it a feel thing. Very tight. It looks like there are some deposits left over on the top of your piston from the gas, but overall a very good burn pattern.

Erik