I picked up a 700 cheap that had a failed rod/crank. I rebuilt the engine with a used crank from the Polaris engine builder in Texas. I used oem crank bearings and seals. Numara pistons and had new valves and seals put in the head. I found the oil relief valve stuck was stuck down to the bottom of the hole and had a very hard time getting it out. I honed the hole and replaced the valve with a small block chevy dowel and got it to slide nicely. New oem valve lifters and head bolts. I cleaned the cases thoroughly and sprayed brake clean through the oil passages with compressed air. Everything was meticulously assembled and torqued to spec.
Engine started up nicely and ran great for the first 100 miles. I dropped the oil and changed it for the break in period. 25 miles later it starts knocking. I pulled it out and the passenger side rod is starting to let go. I'm pretty sure its the same side as the original failed rod/crank. I deleted all my pics of the first tear down.
I'v rebuilt several engines in my time and this is the first one to fail on me. So I'm scratching my head over this one.
The engine builder who sold me the crank will sell me another one for $100. I paid $200 for the first one. I believe this was just its time to go. He says if it was bad it would of failed in the first few miles. But how can you know what the journals look like when you can't take it apart and inspect them before selling it?

 

Hi,
l wanted to find out if you have any experience with Polaris sportsman 700 motors. I wanted to find out some info about rebuilding my motor.
. Thanks Joseph

 

this is my first small engine motor that is designed like this one. All the other motors have roller bearings. The Polaris 700 has a sleeve type bearing on one side of the crank and all of the balance shaft. IMO its a dumb design. I'll never touch another one from now on.

 

Hi,
.. Thanks for you response. My quad was running fine driving along and just stalled wont start just backfires after awhile. Checked spark gas etc everything was good. Just cranks and then backfires wont even start with starter fluid. After reading up about the problem they are saying my cam lopes are wore down and it throws off the timing.
like you never rebuilt an ATV motor rebuilt other type. So I will try to rebuild myself. Thanks again Joe

 

I would do a compression check and see where its at.

 

I didn't that already compression in both cylinders was to spec. Got gas, got spark both cylinders just cranks and then backfires after a few minutes never runs and stalls just backfires.

 

Is the carb dumping too much fuel? Remove the air filter assembly and look down the throat of the carb and see if youre getting a fine mist coming out of the jet housing. If that's fine then you should remove your valve cover and see if your rockers are getting good lift. There's no chain on these. Cam is gear driven.