Geronomo...I'd check into rejetting the beast...I'm in Northern Lower Michigan and the beast needs to be richened up for the below freezing conditions we have here. I dont ride it in the minus 7 degree weather we have now, but you need to really let the 2-stroke warm up for a good long time before riding it.
I know you were riding it for a while before the problems happened, did snow clog the fan area and prevent it from turning without you knowing it or did it block the radiator fins?
I dont think the oil injector froze, I think you probably just ran the beast at full revs for too long so you could ROOST you buddy with snow...(I know I would...HEHEHE)...anyhoo you cant keep full revs on it for prolonged periods of time with the stock jetting because the rush of the clean cold air at full throttle is putting your engine into a LEAN condition.
.....melting pistons I think...would be the out come of constant full throttle operation.....please rejet and then give your buddy some more ROOST FACIALS.
Im no expert on these thinks but Mod Quad, BUBBA , Rick Ritter and tons of others can give you the real poop on Re- Jetting after you rebuild her....Good Luck....HANKERS

 

IF THERE ARE ANY PIECES MISSING FROM THE PISTON
make sure you check to see if the missing debris is in either the caes or the pipe
a few times i have seen the pipe stuff the melted pieces back into the cylinder and score the jug

 

This was a freak snow storm and cold streak. It doesn't normally get below 50 in any of our riding times... at least where I ride. So although I definitely agree that jetting is likely either the culpritt or a contributor to this failure mode, I don't think that I am gonna rejet it cause it worked fine in the normal 75-95 degree weather that it is usually accustomed too. Thanks for the idea though. I think that makes a lot of sense and was likely a problem. The radiator fan did work as it came on and off many times while we were riding. I also think you (HAMMERINHANK) were right on with the roosters in his face. It was too fun peeling this thing out in the snow. So again that was probably some of the reason for the failure.

To be sure, I am gonna check on the injector before I start it up. make sure it is doin its job before letting it do all the work of lubricating.

baxy, thanks for the headsup, I think I am pretty safe because I don't think that it ran very long in this shape. I lost compression and it shut down. As far as I can tell it appears that all the missing stuff ended up on the side of the piston and in the exhaust in the form of very small particles of aluminum stuff. I scraped all that out of the first stage of the exhaust (about a foot) and out of the exhaust port.
This has been a great learning experience for me and I think that what I have learned is that I don't like 2 strokes. They are very simple in theory and operation, but everything seems soo much more dependent on perfect operation. Even the slightest thing changes (altitude, temp, Blood pressure, angle of ascent or descent) and the mixture is off and all Heck is breaking loose. I think that after I get it running again for an extended period of time, I am gonna sell it and maybe get the 500 4-Stroke. I just like those better in my amateur opinion. I like riding better then fixing...

In that tone, with this particular model of atv's is the 4-stroke a little less picky? I know that with my past experiences with 4-strokes they dont care what happens as long as they have gas and oil and air and a small amount of TLC they just keep puring. I currently ride a 2001 wr250f. The quad is for my girl, I dont ride it usually I just break it... I WR runs like a top no matter what I toss at it.

Well thanks again for all your help guys. I am gonna post some of the pics from this rebuild on my web site that I just started. when I do I will post a link.

geronamo

 

If you had melting on the top of the piston you had a lean burn down. It was not an oil issue. It would take a seriously cheap oil to turn to goo at 20 degrees. You need to jet the thing a little bit fatter the next time your pushing it in the cold that hard. See a lot of burn downs on sleds. Jay

 

I am pretty new to 2-strokes so this may be a dumb question and I may be getting too far into this stuff for my experience level... but what you (Polarisboy2) said doesnt make much sense to me. I don't doubt its validity but I just don't understand it.

If I had a lean burn how wasn't it an oil issue? When you say lean I am guessing you are talking about the oil/gas mixture. I was already guessing that was the problem and I would figure that the oil would be more viscous (thicker) at 20 degrees (riding conditions at time of failure) then it is at 85 degrees (normal riding conditions). I also know there was a huge amount of snow around the injector. My thinking was that the oil became thicker and did not flow as freely at that temp causing the lean (with resect to gas/oil) condition.

Or maybe you are saying that rejetting to allow a richer gas oil/air mixture would have made things cooler. I think that with this quad the gas/air mix is independant because of the injector. even with more gas per unit of air I don't think I will have any more oil in the cylinder. Maybe one of the veterans of this machine could clue me in on that.

In either case I want to find the original cause of the problem before I ride again. I am not expecting to ever ride in the cold again because it is never very cold here. I always ride in the summer when it is usually 85+ degrees and often in the high desert so rejetting would cause more problems because there is much less air at 100 degrees at 6000 feet then there is at sea level at 20 degrees.

And as someone from middleburg hts, who moved 2500 miles away I am interested in where you ride in ohio. I graduated midpark 98
and often consider coming home...

geronamo

 

The melt down of your piston was caused by the air/fuel mixure being too lean (more air than fuel) - the easiest way to describe this is using a torch as an example. If you add more oxygen to the torch, the flame gets hotter. Cold weather causes the oxygen in the atmosphere to become more dense - therefore giving the carburetor more O2 than normally, resulting in a lean condition. The solution to this is to add a bigger main jet to compensate fuel for the additional O2.

A lack of oil would have caused the rings to sieze to the cylinder wall, or for the crank/rod bearings to seize - the oil is basically dependant on RPMs - as long as the initial volume setting was correct - ie. pump adjustment is set. Like someone already said - it takes REALLY cold weather for even cheap 2 stroke oil to thicken.

 

geronamo, it is a common misconception that rich and lean have anything to do with oil mixture. Rich and lean only refer to fuel to air ratio. Fuel is was cools the cylinder. You could actually lean a fuel mixture by adding to much oil in a premix. The exact oposite of what lots of folks think.

 

The reason it has to be the lean condition is because of where the melting is. If the top of the cylinder is melting then the heat was coming from the combustion chamber not below the piston or the sides of the piston. Like was said an oil issue results in blown crank bearings and siezed cylinders. And in the injected two strokes the oil is mixed in the crank with the gasoline. That is why you still burn oil even with the injecter. The injecter simply controls the amount of oil that is mixed with the gasoline. I had the same questions when I started working with 2 strokes so don't worry about them. That is how we all learned. I have been working with sleds for years now and have seen the left overs of a few lean burn downs. Top of the piston is the first to go. Jay

 

Well I thank you all for the lesson. That makes a lot more sense now. So if the cold air was the main cause (combined with high revs) I could assume that at my normal operating conditions (90 degrees 2500 - 6000 ft) I wont run into the same thing, because I will have hotter thinner air making for a cooler burn?

If to lean was my culpritt because of the cold air then I will double check the injector for operation and then I shouldnt have much more to worry about.

Thanks again for all your help... I would owe you guys lunch if I knew where ya lived...

Geronamo

 

cut 2 2 inch diameter holes in the air box
plug them with solid grommets
jet the carb to run in the winter with the plugs in
in the summer remove the plugs and the extra air flow to the airbox with let it run at the proper mixture

works on my 2000 xplorer 250
only problem is crossing deep water
although if you have ever gone through alot of water with an xplorer you know it dont like to get wet past the bottom of the seat on a good day!!!

have fun