Hi everyone- Just would like a little insight on this situation.I have a 2004 Polaris ATP 330, 4 stroke. I bought it used and not running from someone that bought it as a project atv but didn't have time to work on it, so I purchased it not knowing why it didnt run. I was in really good shape with only 178 miles on it and only about 14hrs on it. Must have been ridin hard for a short while then not at all for years and garaged. I tore the motor down and it turned out the lower rod bearing was spun. I did almost a complete rebuild on the motor. All new parts(gaskets, bearings, rod, crank, rings, wrist pin, etc) except I did not replace the piston itself due to the fact it was still in great condition as well was the cylinder. I changed air filter, oil filter, rebuilt carb, new polaris oil, etc. Not to mention when I did the tear down, this 2004 atv was like new, in great shape. Anyways, after the rebuild it ran great this winter the first few times I had it out. Although it did have SLIGHT valve tap on the intake side that needed adjusted. Eventually it started to get a little harder to start and to keep running this winter. I only had it out this winter and it was in the single digits to teens each time I had it out, and I did let it warm up quit a while before each ride. One evening I was heading out ice fishing and it began to lose power and hard to keep running so I took it back in. Next morning I took it back out again where it was a little hard to keep running at first then ran fine. I ran it (no more than 15mph) for about 10 min then shut it down and would not start after that. Sounded like it was locking up, or dead battery(symptoms). Almost forgot to mention I did get it started a few months later and it did form a prominant knock, and I quickly shut it down.Finally, got around to tearing the motor down this week. Was expecting another spun lower rod bear. Instead I found the piston had started to seize along w the wrist pin. So, with the top end off, I could just barely move the piston forwards and back. Everything else on the motor looked just fine. Rings and cylinder wall looked good. No play up or down in the rod, just a minute wiggle left n right, lower end spun smoothly. Ohhh, I drained the oil and did not find metal shavings, oil still looked new as well. Wondering why it froze up there. Oil pump checked out fine in first rebuild, rings were put in correctly, and end gap was checked. I still have yet to check the oil line hoses. I did start to develope a very slow leak in both hoses at the motor side. Wondering if maybe I developed a small blockage some how. Anyways, wondering what u all thought???????I will keep u posted on my findings. Thanks

 

ALWAYS have a cylinder and piston measured! Even though a piston may look "good' the factory clearance between cylinder and piston is by the book about .0015 when new! Considered "worn out" when reaches around .0025 by the book. If piston has .004 or greater clearance,will "slap" against cylinder wall and seize up! Have a dealer or machine shop measure ,order an appropriate oversize WISECO piston kit and have them bore and hone to NO MORE than .0015 finish clearance! Hopefully this will solve your problem and that the upper rod piston pin clearance is not damaged beyond use and rod has to be replaced again!
PS also when you replaced the rod and lower rod bearings was the crankshaft rod journal scored in any way from the old rod and did you have the journal measured? OPT

 

OPTI agree, I shoulda measured the Cylinder and piston. I slacked there and didn't because a local polaris dealer mech told me it should be just fine if the piston and cylinder looked good still. Upset w myself there cuz I was cautious with evertything else.I have another question for you if you don't mind.... How concerned shoud I be this time about the bottom end of the motor, with the symptoms I encountered this time? Anything I should particularly check??? With the piston and wrist pin starting to lock up. I still am going to take the clylinder in to see if I am going to need it bored out with an over sized piston. If not I will still have it honed before I put the new piston in this time. I am thinking it's not gonna need to be rebored though, but I could be wrong.THANKSKELLY

 

The main thing I would be concerned with is the condition of the crank journal when you replace with the new rod and bearings.That's why I asked was it scored,discolored from heat,etc. I always measured the journal diameter against the tolerance specs, You probably can get by with it as the plain rod bearings are what wear down first (soft metal) IF in doubt,you would have to tear back down! The rod should be able to move fairly easy and smooth on the crank and NO up and down play,a little side to side play is acceptable,I would let the dealer look the rod over too! OPT

 

I missed your PS on your first post. When I rebuilt the motor the first time, I replaced the crankshaft with a new one. I had the old crank journal measured and it was unable to be saved.

 

Good deal! Hopefully just a new piston needed. Keep us updated. OPT

 

OPT- I have a questionI just got my new piston in today. I don't have my atv here at home but will be at the shop tmarrow to look at it. Although, the new piston is different on the top than the origional (supseated). The two indentations on the top, are they called valve releifs? Well, on the old piston they were both the same size, on the new piston, one is smaller than the other. Why is that??? Part number on the new piston is the correct one. Also, the new piston has an M printed on one side (Left or Right?). When installing the new piston, which is the correct placement?THANK YOU VERY MUCH for your Help!!!!Kelly

 

Smaller "relief' cut on piston faces exhaust as intake valves are larger. OPT

 

Thank You OPT. I have the manual, but it did not tell me that. Much appreciated. I'm sure I could have figured it out tmarrow when looking at the vavles myself.

 

A lower rod bearing with that few hours. Sounds like the engine was ran low on oil.

I have torn down engines that were run low on oil and a tight wrist pin is classic along with wasted lower end bearings and crank. You could see where things got toasty if you know what to look for...........or even smell for.