new piston??

[trailrider894]

so i'm gonna be doing a somewhat of a rebuild just on the engine on my ex. and i'm wondering if i want a new piston. what kind of piston is best?? and if i open it up and the cylinder walls are scared or anything what should be done about that?? and what all should be done if i gonna replace the piston? and what about bumping up the compression?? not sure what stock compression is ?? but i'm thinking about bumping it up. what would you guys recommend upping it to. i don't wanna have to buy special race fuel though. i already run the highest octane pump gas the station has to offer. a-lot of question so sorry.

[bry14661]

open it up and look before you order parts and if you dont know what to look for just take it somewhere

[Wheelie]

Buy a JE 10.8:1 87mm piston, punch the cylinder .080 over and you'll be set. The cylinder will be clean, good power gains, no sacrifice in reliability and still be 93 octane friendly.

[trailrider894]

what is punching the cylinder?? never heard the term before.

[78ta]

he means boring the cylinder oversize

[RaceinCircles]

I just finished my first rebuild and I put a forged Wiseco 11:1 compression 89.5mm piston in my 03ex. Before you do anything you need to have your cylinder measured. I knew I needed something done to mine because it was pouring smoke out the exhaust. That meant that there was oil going up through the rings on the piston. Stock clearance for the piston I believe is around 2 thousandths and mine had 6 or 7 thousandths. Stock compression is 10:1. I chose Wiseco becuase they are a well known brand. JE also is known to make a great piston. You will need a Piston, a gasket kit, an oil filter and 2 quarts oil. About the compression, as long as you don't bump the compression up to 12:1 you wont need any special fuel. Running the highest octane is what should use. I am very happy with my choice of piston which takes it from 397cc to 406cc. I'd check ebay for a piston and then find out who the dealer is and contact them directly. It'll probably save you around 80 bucks going this route then to a honda dealer.

[RaceinCircles]

Oops...That should be 85.5mm. Stock standard size is 85mm.

[hypersnyper6947]

Stock piston is a 85 mm, to go to a 406cc its a 86mm, the guy above i incorrect. I am pretty sure stock compression is 9.1:1 or something close to that, not the 10:1 as stated above, once again incorrect. Your motor could also smoke b/c of valve problems not always b/c your piston needs to be replaced. By the way a 89mm piston is what you use for a big bore 440 kit.

[RaceinCircles]

I'm pretty sure to get to a 406 you bore 20 thousandths over and you buy a 85.5mm piston. With the amount of smoke that was coming out of this thing there was no way it was a valve problem. You must have missed my own correction on the 89...

[hypersnyper6947]

Yep i did miss your correction about the 89 my bad.