I just bought a ATC 250R yesterday. The problem is
the top of the piston and head looks like it has been shot with a shotgun. It is pitted real bad.
I was wondering what caused this and what is recommended to prevent it from happening again?
I generally work on 4strokes,and don't have a lot of experience with 2strokes. Also does this bike always get bad fuel economy,it is terrible.
The engine has not been bored and is in dire need of it, what would be a good piston to put in it.
Does anyone have one for sale. Thanks!

 

To me it sounds like the former owner blew up the engine at one time or an other. There are a few conditions that cause this, 1 the engine leaned out too much and caused the top of the piston to get hot and start to melt, this could be a carb problem. Or you got water in your gas and it cause the engine to again lean out. You did not say what year your ATC is. 81 to 84 are air cooled and 85 to 86 are liquid cooled. Another problem that cause the engine to lean out was an air leak at the cyl base gasket. If the head is pitted badly like you say you should have a machine shop smooth that head out for you. Yes it is normal for a 2 stroke to get bad gas miliage thats just the way they are. If you have ridden 4 strokes most of the time and now you go to 2 strokes you will never see the great gas miliage of the 4. Take the cyl to a good motorcycle shop and have them mic. the cyl for a "out of round bore" and then have a new piston put in. They'll tell you how far it will have to be bored out. There are a lot of good piston companys out there but I personally use Wiseco pistons. Hope this helps and good luck

 

The top of the piston being pitted along with the head being gouged is a tell tale sign of a bottom end failure. The crank or crank bearings probably gave way. You can get the crank rebuilt, which is cheaper than a new one. New crank bearings should be installed as well.

 

Mine is a 85 model. The bottom end is tight and has no excess play. I thought maybe it had leaned out but wasn't sure. I haven't seen one do this before. I have a 350x and I just put a Wiesco in it. A friend suggested a Wiesco ProLite.
This bike screams like there is no tomorrow, but I would like some ideas on how to make it better and more dependable. By the way it is an ATC 250R.

 

I really appreciate everyones help

 

Hang on..before you go out and split the cases to rebuild your crank, take the piston and cylinder to someone to look at in person. You should probably take the entire engine too. There are many things for that could have caused the pitting, especially being old and never having been bored. So, get a first hand second opinion. There's no way to tell you for sure what caused it without seeing the entire thing. Just really good guesses.

As for the head being pitted, I heard a former National Champ give an interesting suggestion. The head really doesn't have much to do with smooth flowing(not talking about volume here). Having a slightly pitted head can hold a little extra oil/gas(kinda like a reserve), so it could help the piston stay cooler on a short high rev. I don't really know, but there could be something to it. He never smoothes out any of his heads. Oh well, just another idea.
Good luck.

 

I heard if you don't smooth the pits, the high spots that stick out will get hotter and even get hot enough to glow, causing pre ignition. This might be a bunch of bull, but it makes sense to me.
ERIC