Posted: 20 - July - 2010 at 07:30 | IP Logged

Hi All

In the middle of a rebuild and in order to restore compression back to spec, I'll likely need to go to 1st oversize on the pistons. Soo I was wondering if boring out to fit 25 hp pistons is all that is required? I could use the 5 extra hp!

All responses welcome

Bill

Posted: 21 - July - 2010 at 22:31 | IP Logged

if you oversize the bore too much ie taking a "20 hp" motor to a "25 hp" motor on a aluminum block it weekens the side walls way too much and maybe even the valves might provide major problems..

if it was a cast iron block maybe.. if it was heavy duty..

the reason for the "quote" marks is some how small engines have been measured in cubic centimeters not cubic inches.. there is/was major international class action law suit..

Posted: 22 - July - 2010 at 18:07 | IP Logged

Don't think it's a good idea either. If I remember right, thow are cast iron sleeves. If ou take that much away, it will crack. It could possibly shrink with it being that thin and cause troubles. Not too sure but the piston skirts may be different lengths as well causing either wobble or a skirt possibly hitting the connecting rod.

Just like Tom said go with the available siz pistons for that engine. If you can stick to the closest to stock like .010" so you can save as much on the cylinder in case of another rebuild is necessary down the road. just 2˘.