Hey guys, got a question. Well awhile back I was riding my 1990 650 that has some mods and well it turns 10,000 rpm quite easily! When it ran it was a monster. I kept having troubles with it and found I had a bunch of gas line leaks because of it sitting for 4-5 years with a bad pto crank seal and bearings. I put new gas lines on it ran good for about a day then more problems, I then found out it was a bad fuel pumo, replace that and a few other things like electrical problems then it ran like a monster, nice tan plugs and everything. Went to go for a ride and it was a new machine, I left went doen the straight away by my house at night with the front end off the ground, i knew trees were coming but the headlight was in the air so I let off to take the turn ahead so I didnt hit the trees. So i made the turn and went to get on the gas again it just died, It didnt make any noise or anything. I checked compression it was great on all cylinders, I let it cool doen then started it back up again and felt all the pipes and the pto cylinder was ice cold, I took the airbox off thinking it was the carb and I put my hand on the carb and it fired on all 3, I take my hand away and it dies, It was a huge stumper for everyone on here to figure it out. Well I got to thinking about the sled again and I took it apart today. As someone had gave a thought of the piston skirt being broke- they were 100% correct, It broke off really high on the piston. I looked at the other 2 cylinders and the center is perfect and the mag side has a really large crack already on the piston and it too is ready to go. The pto piston is a cheap aftermarket and it was almost new when i got the sled going again- it was bought already and installed so i kept it in. This is the series 1 engine without the skirt helpers on the cylinder. I have a completely modified topend for this engine, it is bored some(i think) ported polished intake and exhaust and has bigger oil injection holes for the cylinder. It also has machined cylinders for O rings instead of head gasket- this is for higher compression. This top end I wanted to put on it is also a series 1, i have a complete rxl engine that is the series 2 engine- all it needs is a piston as it had blew a head gasket leaned out the cylinder and made a hole in the piston. The bottom end is all new on the engine I have aswell as the bottom end to the modified topend- the top end is off of it, the rxl is all apart so the base halves are out incase I should use those cylinders. I need to know If I shoudl use the stock top end thats on it- use the modified which I would really love to use as thats why I bought it- or use the stock rxl top end with the top half of the base to go with it. Either way I have to get one piston or 3. If I go with the modified top end or the stock one that is on it now what kind of pistons should I get that will not break the skirts? Is it even worth it to put the modified top on it as the piston skirts are prone to breaking on these series 1 engine? Thanks alot, sorry for the really long post, Brian

Brian,
I believe Polaris introduced a HD piston for the 650 with the numbers 65C. These are designed to reduce piston skirt breakage. Wiseco is a good second choice, but apparently don't seal the cyl as well and make a little less hp.
I've owned a TURBOCHARGED 89 (01)and a 91 650 (02) and always used either the HD Polaris pistons or Wiseco. Never broke a skirt.

Hey I pm'ed you, I didnt read this post before I imed you tho so let me know what you have for good polaris pistons. Thanks alot, Brian