I was wondering if overboring creates any extra power for having a larger surface area, or does it just regain lost power from the the cylinder as it is worn and honed? Just wondering whether its worth doing, i honed the head quite hard when i did top end as when i bought it in April from my mate the piston had scored the head quite bad. Its running fine but was thinking of doing the porting (been watching the Ken O Connor videos!!!) and was wondering whether to have the head overbored. Cheers
Quick question about overboring
- Thread starter Jaffa
- Start date
Blaner
Your Friendly South African Ambassador
have the head overbored? are you talking about the cylinder or the head now? Putting in an over size piston will give you a bigger capacity cylinder, use a simple volume of a cylinder calculation to work it out with your new radius of your piston. If you are talking about milling your head, just a fat skim over the bottom wont help much, the blaster have a poorley designd combustion chamber ON PURPOSE by yamaha. Research it carefully and then take it to someone who knows what they are doing.
Blaner
Your Friendly South African Ambassador
one thing to bear in mind is that a larger diameter piston has greater surface area and hence greater friction between cylinder and rings meaning greater wear. Just a thought.
Overboring a piston does not add signifcantly to either the friction or volume. The main purpose of boring a cylinder is to clean up any damage so that you have a good surface for the piston to slide against. Don't bore a cylinder any more than necessary to get it back up and running it won't result in any more power.
Go for the DIY porting, if you follow Ken's instructions you've got nothing to lose. What he shows is how to clean up casting flaws and change the exhaust port height slightly. Anything more than that you probably need to send the cylinder to an engine builder so they can dial the cylinder in to your specific needs. Remember, the porting on a 2 stroke is the intake, exhaust, and power stroke and even small changes make a big difference.
Go for the DIY porting, if you follow Ken's instructions you've got nothing to lose. What he shows is how to clean up casting flaws and change the exhaust port height slightly. Anything more than that you probably need to send the cylinder to an engine builder so they can dial the cylinder in to your specific needs. Remember, the porting on a 2 stroke is the intake, exhaust, and power stroke and even small changes make a big difference.
If you honed it that much, chances are you have excessive piston clearance now and probably aren't sealing as well as you could, not to mention the danger of piston slap breaking your piston skirt. Just the smallest overbore possible to true the cylinder, a new piston and rings, will do nice things for you. Definitely, do this after you do your porting.
Thanks for ur responses, its running fine at the moment, compression is good, so i wont bother with looking into overboring just yet. With the porting i was just planning on doing the exhaust to begin with. If anyone has done it, and if so how are the results? Cheers.
While you have it apart, measure the cylinder and piston to check clearances. Excessive piston to wall clearance kills motors. Seriously.
