Bore kits and how they work

[welfareglasses]

Can someone tell me what happens when you bore an ATC. What does this do and what benifits will you get, horse power change? What steps do you go through to bore polish and port a bike?

[twoodward15]

You "bore" it out, not boar. Anyway. When you bore the cylinder you are making it bigger. It usually goes in .010 increments (ten thousandths). Technically I guess you should see a bit of difference in horsepower when tested on a dyno. If you leave the compression ratio the same ie. use a stock piston and don't shave any material off the jug or head then it is going to be roughly the same horse power as stock. You WILL notice a difference if you rebuild a worn out motor because you have lost compression from worn rings and such. basically what I'm getting at is that people rebuild their motor and think they are making ungodly amounts of hp because it runs so well after the rebuild when in all actuality it is running at roughly stock horsepower. Ok so that covers your basic bore job.
Now you want to talk about porting and polishing. You would be talking about porting and polishing your intake and exhaust runners. Hmmm basically if you don't have knowledge or a flow bench you shouldn't be doing this. What I am assuming you are really talking about is simply cleaning up all of the casting flash that leaves a rough surface in these same runners. That would be a good idea as long as you know what you are doing. Now, I have a honda 185s. I could clean all of this up but if I wasted the day to do it then I'd be wating my time. It really isn't going to be a noticeable hp gain. If I had a two stroke and could really spin the motor (high rpm) then it's make a noticeable difference.
Now my suggestions to you are to rebuild your worn out motor and don't worry about the porting and polishing. A stock rebuild is going to make you think you have a new bike again. You will gain horsepower, but it's only going to bring it back up to stock levels unless you add a high compression piston, shave the head or jug, or use a thinner gasket between them.