i have a 96 300ex and i bored it out 40 over but it smokes like a train and i changed the valve seals and i have no idea y it would still smoke, do you think they bored my cylinder to big for the piston so now it goes down and brings up oil.

 

i have two theories, one is that you are correct. Second, is that valve seals aren't everything. Honda valve guides definitely are not the most reputable parts of their engines. I assume you checked the play btw stems and guides? basic wiggle test? lemme know more about the valve assembly.

 

Did it smoke before you rebuilt or just after?

Are you sure the rings were installed correctly?

I'm assuming the person boring the cylinder knows something about engines and had the new piston in hand to measure it before starting to bore the cylinder. Every piston must be measured, just because it is a 67mm piston doesn't mean it's exactly 67mm.

If the engine smoked bad enough befor the rebuild, it will take a few hours of riding to stop the smoking completely because of the oil buildup in the muffler.

 

the valves dont wiggle, the rings r in correctly, they had the piston when they bored it, and it makes noise.

 

does anyone know what i should do i m trying to get this fixed for a christmas present.

 

i would do a compresion test. then i would pull it back apart and inspect the piston, bore, and rings.