800 cfi Piston Replacement
- Thread starter pj8556
- Start date
where does polaris spec their piston size? At what point on the piston is it measured? The polaris piston has a 16 thou taper from top to bottum, so are they measuring at the bottum? Also How much gap is neccessary between the cylinder skirt and the fly cut on the upper case? Is 5 thou enough? Our cases are rubbing on the upper case..
Got my "fix" kit late last week. Tore the engine down friday and found some bad scoring all on the intake side down low on the skirts of both pistons. I kept checking for scoring through the exhaust valve port and found nothing. SO, in my opinion just checking for scoring this way through the port is not good enough. Cylinders look really good, can still see cross hatch. Going to have them honed anyway. If anyone has any doubts about their pistons, I would get the fix kit. With mine it would have been a matter of time before a 600 dollar bill turned into upwards of 3000. Putting it back together tuesday. Will report back when its up and running again.
10mm up from the bottom of the piston. It is a very small area that will measure the widest.
M
minus40
Well-known member
BB 800 piston VS CFI version
Skip to bottom if you don't like to read.
Dug out an old elko piston to compare to the cfi version. Very rough measurements so don't take them as accurate. elko about .078 taller above pin and skirt was about .006 shorter. Installed in a 2010 cylinder the rear intake transfer appeared to be open the same but the front was closed off more. Looked like a modification would be easy enough. One area I didn't get into much was the pin relief in relation to shorting out the intake and ex sub ports. Also the elko had much more dome.
One interesting thing, I took off the top ring on both pistons to make it easier moving in bore. The elko had a much stronger ring. The cfi (asso ?) piston moved a little from gravity in the bore. Low tension rings? Crappy rings? Both used pistons, the elko has a nick from the ex valve and the other has light scoring on intake side and signs of blowby. Elko .002 bigger dia.
In summary, use something else unless you want to grind, shim and buy a custom head.
Skip to bottom if you don't like to read.
Dug out an old elko piston to compare to the cfi version. Very rough measurements so don't take them as accurate. elko about .078 taller above pin and skirt was about .006 shorter. Installed in a 2010 cylinder the rear intake transfer appeared to be open the same but the front was closed off more. Looked like a modification would be easy enough. One area I didn't get into much was the pin relief in relation to shorting out the intake and ex sub ports. Also the elko had much more dome.
One interesting thing, I took off the top ring on both pistons to make it easier moving in bore. The elko had a much stronger ring. The cfi (asso ?) piston moved a little from gravity in the bore. Low tension rings? Crappy rings? Both used pistons, the elko has a nick from the ex valve and the other has light scoring on intake side and signs of blowby. Elko .002 bigger dia.
In summary, use something else unless you want to grind, shim and buy a custom head.
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