I just took apart the top end on my '99 Banshee and I'm not sure how to tell if has been bored or not. I know the stamping on the top of the pistons will tell me, but I do not know waht the #s mean. I have a Clymer manual on the way, but I want to get the cylinders bored ASAP. I purchased a set of .020 over pistons in the hopes that it still had the stock bore. The pistons that came out just have one row of numbers "dot" stamped on the tops. Any suggestions on how to tell what the piston size is?

 

If i were u, I would stay with stock and find someone who is really good with porting..for pistons, i would run wiesco hig comp..boring out the engine will just lower you lenght of time you will get out of it....

 

Hey, just check the bore with a set of dial calipers. that will tell you what the diameter of the bore is. If you dont have a set of calipers go to a machine shop or an ATV shop. They will be able to tell you what bore it is on.

 

I already found out. It seems I have wasted money buying .020" over pistons, because the cylinders are already.060" over. But I will save some additional money because the machine shop said they can just hone the cylinders instead of boring. They aren't as bad as what I had remembered seeing them.

 

running stock pistons is acctually a plus...if you think about it...Yamaha had taken so time to fine tune the engine to run stock...the engine's were not made to run bigger...that is like introducing a animal into a new enviroment. A banshee with a stock bore and the right port job, will beat a ported bike that is 40 over running on alcohol. it all has to do with the port work...