nick34

hey guys i have a situation i need help with.. a few months ago the ski ran like crap so i checked compression and the pto cylinder was gone 40 psi so i pulled head and the piston had a hole in it dead center the size of a nickel i replaced it with a new piston and rings.. i installed new gaskets and bolted it back up.. when i tried to start it it would fire so i pored some fuel down the carbs and tried again and again it.. nothing i pulled plugs to check for spark and it has spark when i put the plugs back in and hit the button BBAAAAMMMMM BACK FIRE so loud my wife tinkled alittle lol so after doing that a few times i decide to pull the pto plug and check compression again holy crap 40 psi still so i pull the head and it is in great shape nice and tight.. i put the head back on torque it down and try to start it with the plug out in the pto cylinder and it starts up everytime but as soon as i put the plug in it will not start only back fire every once in awhile..


what the heck could it be

a hole in the case or a bad crank seal ????

why no compression???

nick34

ttt please any comments

mrjetskey

IT backfired because of fuel and air in the waterbox however,You have to find out what caused the piston to hole out.You only fixed the problem piston,not the problem that caused the piston to hole!!!Chances are depending on the model,I would think that your timing is off caused either by stator/flywheel ,IF the piston was burned across the exhaust side I would say lean condition,but since yours holed in the middle,it could be anything from stator/flywheel,to crankshaft indexing being out,did you ever turn ski over and get water in it??,did you pull engine and clean out crankcase very well and check bearings on crank???You have a lot of things to check out.Its easy to fix or install a new piston,the hard part is figuring out what caused it.THats where sometimes it takes a lot of time and effort to run down.Many polaris models had trouble with flywheel trigger and magnet moving loose when set screws broke,altering timing!!hope this helps>Marvin

sl94

Just a thought, you might want to make sure you don't have any broken reed valves. Just assuming your are talking about a 2 stroke polaris. Usually holed piston means lean condition, not always, but usually. Could be dirty carbs, bad fuel pump, bad pet****, bad fuel line..... you definetly need to figure out why you burned a hole, or you will probably do it again. Just wondering if the spark plug on the pto cylinder was white? If so, you might have a crank seal leaking and could definetly cause a hole.

nick34

thanks guys im goint to pull motor and check atleast the reeds and stuff but im wondering why i still only have 40 psi on a new piston and rings ??