If your P/C measurement is correct, piston to cylinder clearance sounds iffy on the type A pistons,but probably can be ok. Here's what the manual shows. Cylinder to Piston Clearance .0015" ± .00059"(.040 ± .015mm)
which is pretty tight as most 4 strokes are. Don't know if B or C would even help that much. Ring orientation like most 4 strokes is end gaps staggered,away from intake,exhaust ports. I always had both compression ring ends opposite of each other behind the piston pins. Stagger the oil rings also.

 

Thanks OPT for all the help, Got it all back together and running, no smoke or noises, runs great as before.

Ran it for 5 minutes, dumped oil and filter, it was very chocolate milky.

Replaced oil and filter, ran 15 minutes, got the cooling system burped. 2 fan cycles. Dumped oil and filter again.

This time it looked like decent oil with a VERY VERY MINOR discoloration. Do you think its safe to put in the good oil at this point? How long until I should change it again?

 

Sounds like it's safe to put the "good stuff" in now. If mine I'd change it out just like breaking in a new one,20-25 hrs or less depending on how you feel about it. Glad you got her up and running. Keep us updated as to whether the coolant leaked is fixed for good now after you put a few miles on it along with how the Namura pistons are doing as far as ring seating,any smoking,etc..

 

Got 3 miles on the quad today. Ran perfect. No oil/water contamination. No smoke. Only issue I have noticed off hand is the upper radiator hose is leaking pretty good at the thermostat housing, so I need to order that or see if its a normal size I can just get from the auto parts store.

Also the ignition will not shut this thing off, have to use the handlebar switch.

 

Odd ball hose as one end is flared out. Most online places show Nla. Here's a used set up on ebay. The hose is the one at the bottom #5412030. (used on the 600 also) 2004 Polaris Sportsman 600 4x4 Coolant Coolant Hoses 5412312 5412313 5412030 | eBay If at all possible to splice it? Seems strange though.. Most hoses are just 3/4" and you can get at any auto supply.. Check the switch connections/wiring. Expensive on this one if switch is bad. 4012164.4012164 Polaris | eBay

 

I feel stupid, got the line spliced with all new, went for a ride. Still leaking. Looked alot closer and found a pinhole in the small 3/8 line going into the head. Just had to cut a small bit out and now leak free. Hopefully the plastic barb fitting with hold up to the heat of the coolant on the big one. They did not have it in brass.

Also, unplugged the ignition, put a little dielectric grease in the plug and its working again.

 

Just sold this atv today, and I allready miss it. Coolant leak was cured, pistons and rings worked great for the hours and miles I have put on it over the last 6 months. It was a powerhouse, no smoke, always ran perfect. Anyways I thought I upgraded to a 2007 Sportsman 800 EFI X2. I will start another thread shortly.

In conclusion. For the money the Namura pistons held up and worked great. I would buy them again if I had to do it over.

 

Good to know the Namura pistons worked out ok. I know a couple people like you.. They'd spend a lot of time fixing up cycles,cars,atvs,etc but after everything was done the thrill,challenge and excitement was gone. They'd sell it, find something else to work on so they'd be occupied and happy again