Well, riding around today, the ATV seemed fine.... going through the woods at mid throttle. get to a little more open area and lean into the gas some more, it picks up speed, but just didnt seem right.
Slowed down some, hit the gas again, same thing.
Came to a stop, and the motor died. Would not restart, had the GF town me back to the house.

Checked I was getting fuel and spark and found that all of that was fine. Then the dreaded compression test [img]i/expressions/face-icon-small-wink.gif[/img]
crank it over, WOW, 80 PSI [img]i/expressions/face-icon-small-sad.gif[/img]

So I tore the plastic/gas tank off, and pulled the head and cylinder off. First thing I noticed after pulling the head off, was some built up oil on one of the head studs.
Then after the cylinder came off, I saw the piston, heh. Nice and healthy [img]i/expressions/face-icon-small-wink.gif[/img].... with the exception of a busted lower ring and a huge gouge down the side. Oddly enough, the oil buildup was in the exact spot the gouge was [img]i/expressions/face-icon-small-smile.gif[/img]

Now seeing as this was the first time I have ever torn down a motor.... I felt the inner wall of the cylinder and I can feel a moderate amount of scoring. Nothing that seems REAL bad, but enough that I am sure it will have to be bored to something a little bigger. How much over do you think I shall need to go, or should I just leave that question up to the machine shop?

Once I know that, I can order up my wiseco piston and the other misc. stuff that I will need.

Here is a picture of the beautiful piston (570K)

I had been planning on ordering a wiseco one of these days anyways, since the compression when I got the ATV about a year ago was ~105PSI, which is very close to the service limit. This just gave me the extra push I needed I guess.

Anyone have any ideas what would cause this to occur? just fatigue over time? improper oiling? anything?

Thanks,
-Chris

 

AAAHHH, welcome to the club ):-/
If its just moderate then Id say .020 over should take it up. But it wudnt hurt to run it to the maching shop for a second opinion.[img]i/expressions/face-icon-small-wink.gif[/img]

 

ya id say 20 would be good also...
and thats just the 2-stroke thing man... they gotta be rebuilt!!!

 

are you going to have any other work done to it while its apart?

 

thewayout420: Probably not going to have anything else done while it's apart.
Just want a running ATV again [img]i/expressions/face-icon-small-smile.gif[/img]

Once it's done, it should be a whole new beast though. Seeing as I have only had it with around 100PSI compression. Should have a little extra go with a new piston in it, heh.

I guess it's good that I got almost a full year of use out of it before it did this. And to think, I just got my new mudlites up front, haven't even gotten to test out 4WD in the mud with 4 good tires [img]i/expressions/face-icon-small-wink.gif[/img]

I tried looking up prices and stuff from RCR, but for whatever reason I can't access their site right now.....

-Chris

 

Holy crap!!!! That thing is smoked!!!!!!!!!!!! Are you sure there is only moderate damage to the cyl. wall?
Good job........that looks like my YZ250 after I ran 110 octane race gas in it!!! If I had wings I don't think I would have landed yet[img]i/expressions/face-icon-small-happy.gif[/img]

 

Paulzaho: Well, in my opinion, the walls are not that bad. In most of it, I cannot feel the scratches at all, feels perfectly smooth.
Only right where that gouge is do I feel a little roughness.

As I said, this is my first time tearing one down. So the machine shop is going to have to give me the true damage.

It appears a piece of ring broke off, gouged the piston and exited out the exhaust.
I cannot find any pieces in the crankcase, the head is untouched, the rest looks great. So hopefully I can just get this thing bored out a little, order a Wiseco and have this thing put back together by next weekend.

Any ideas though on what would cause this to happen? As I would definitely not want this to happen again anytime soon [img]i/expressions/face-icon-small-wink.gif[/img]

-Chris

 

pretty wear out piston,scuffed all over,how long does it lested?
i'm sure you put alot of miles running it,a redbuild with little boring
should take it back tohether fine,check be sure to use good gas
and proper spark plug all the time.

 

That's the thing.
I always let the thing warm up before riding, I always check the plug to make sure its running ok, I really don't think I abuse it that much...
I always make sure to top off the Amsoil synth 2 stroke oil. Everything appears to be well oiled on the bottom end, so I would have to assume that the injector is working ok.

As I had said, it had around 105PSI compression when I first got it, so who knows what the piston looked like when I got it. The engine always seemed kinda loud since I have owned it also. I had questioned that in past months and was told an aircooled motor is generally louder, so I thought it was normal.

Now, you say to make sure I use good gas. I have always been told to use regular gas, and not to use premium as the engine was designed to run better on lower octane.

Speaking of plugs, when I bought the ATV, the first time I ever pulled the plug there was an NGK BR6ES in there. Now, the recommended plug is a BR8ES, so I quickly changed that out.

From the way it looked, this motor had never been apart. So the stock piston has lasted quite some time since it's a 99 model. The previous owners did say they did long trail runs with groups of people. Since it did not come with an odometer from the factory, I have no idea how many miles are on it. I put a speedometer on it about 6 months ago, and it now has 100 miles on it.

-Chris

 

How is the rod bearing, is there much play there? When reassembling make sure to lube all the parts up real good with good 2 stroke oil. Preimix your gas for a couple of tanks as well as run your oil injection. Make sure your oil injection is adjusted properly. Others will tell you to remove it, but I'm against it unless you are a racer and need to save the weight.