If those are OE cast units, then without looking it up, I do believe that those are set as close as .0008" to .0012" on the high limit.
Scott

 

Thanks Scott - your memory of original specs is pretty near (0.00075" - 0.00175") as listed in the manual I have. I am getting the cylinders bored 0.005" so hopefully I will lose that noise I had. Any preference between Cometic or James gaskets? My borer sells and recommends Cometic but they are about twice the price over here. Thanks to all contributors on this issue, I''ll post later when it is back together with an update.

 

Dont hesistate! Buy a new set of oversize pistons< and bore it to suit It,ll save down time and wll be NEW!

"DO IT ONCE: DO IT WELL!" or "DONT do it at ALL"
(our workshops motto)
skull

 

Have checked the inner cam bearing after reading posts on the forum and advice from my cylinder borer - the bearing and cam journal are both good - the bearing is a full complement Torrington. What running in oil for a rebore and new pistons are recommended?

 

Shell Rotella 15W40 for break in and if you do it right, that will happen in the first 100 miles. Dump the oil at 100 miles and run whatever you want after that but change oil and filter at 500 miles. Not an EVO guy but would think that OEM overbore pistons are available. If you want tight tolerances try to find cast.

 

Just a follow up on this topic. Had the cylinders bored 0.005" over size and I reassembled with new pistons, rings etc the other day. The noise has gone and motor feels a little more responsive already, although still running in. Feel very confident in the bike now having checked the inner cam bearing as well, can look forward to riding now. Thanks for all your inputs.
PS One further point that may help others in diagnosing suspected "piston slap" - I noticed that when cruising along at about 2500rpm the noise was quite noticeable but as soon as I either accelerated or decelerated the noise disappeared. Also a bit hard to tell but I think with a bit more load on the motor, say at 120 - 130 km/hr could not really hear the noise. So if you have this issue - new oversize pistons or ride harder!! Cheers