Polaris cylinder exchange... low compression

[mkimister2]

I recently got a Polaris 1200 cylinder exchange and installed it. After following the correct break in procedure for the first tank of gas I took the ski home. When I did a compression test this afternoon before I was going to finish the break in bad news hit. The front and rear clyinder are inbetween 140-150. The middle cylinder is at 25 psi. What could the problem be??? What should be my next step to take? Should I disassemble the cylinder to see if there is damage to the cylinder wall, piston, rings? Can there be a singe cylinder exchange if the cylinder sleeve is scored? Thanks in advance for the help, Andrew

[Technical Support]

Re: Polaris cylinder exchange... low compression

Sorry, no we do not do single exchanges. Yes at this point tear it down for inspection and go from there. What caused your original failure and what repairs were done other than replacing the damaged top-end parts?

[mkimister2]

Re: Polaris cylinder exchange... low compression

My original engine failure was really just low compression on the front cylinder from a piece of the piston breaking off and scoring the cylinder wall. Everything else was okay, but I figured I would replace them all to be safe. I also removed my oil pump since premix assures me that I am getting oil into all cylinders. I will take it apart tomorrow and have pictures of the damage.

[Technical Support]

Re: Polaris cylinder exchange... low compression

Pistons do not 'just break'. Something caused it to happen, and unless the root cause was corrected you will just blow this new set. I suggest rebuilding your carbs and going through the whole engine system. Did you tear the engine completely down and inspect the crank before reusing it?

[mkimister2]

Re: Polaris cylinder exchange... low compression

So, I took apart the cylinder and found that it, the piston, and rings are scored. The scoring is less than what my first cylinder was which prompted the cylinder exchange. I am confused how this slight scoring can cause 25 psi... The piston that broke looked like this :
The break occured inbetween the rings (ringland) about an inch and a half around. That was the only part that broke. The carbs were adjusted about 14 hours ago and seemed fine. I did not look into the bottom end since I thought it was only the top end that needed attention, other wise I would have just bought a rebuilt engine. The new piston is fine except for a couple small marks from contacting the cylinder wall. I will have pictures up later tonight of the damage since my computer is acting up. Until I get the pictures up what would be the easiest way to solve the problem... Could I use an old cylinder and piston and send back one of the newly machined cylinders back? Would this possibly be a solution or would I need to match the oversized pistons and cylinders in the engine? Thanks for all your help so far. Andrew
P.S. For the exchange all I need to send back is the cylinders correct?

[Technical Support]

Re: Polaris cylinder exchange... low compression

Yes, just the cylinders come back. We definitely recommend keeping it all matched. I can't tell much from that picture - get all angles, and in focus.