[beedub]

Has anyone tried machining a groove in the oil pump piston for an "O" ring to increase flow?

 

[tbpmusic]

We all know that oil flow in these piston-style oil pump bikes is a major concern (especially in 450's) - but I've personally never heard of that particular solution.
Considering the speed at which the piston moves, I'd want to ask an engineer if an o-ring was appropriate as a solution. I think I'd be concerned about the o-ring's durability and longevity in that application.
But, I'm not an engineer....

I'd be very interested to hear of any experimental results in that context......I think lots of others would as well.

 

[66Sprint]

A careful examination of the oil pump piston will give you the answer.... It will show "travel marking" or scuffing not unlike the big piston(s).... This is due to the difference in expansion rates of the differing metals "closing" the clearance when the parts are hot.... The viscosity of the oil itself acts as a "ring" sealing the assembly while it pumps.....If the pump is good, it won't appreciably "back-leak" even when cold, however, this is one part you should oil as you assemble it so it has oil film on it before it starts moving....Once in the engine, the proper "fill level" will maintain that film.....
BTW A "ring" would NOT increase flow rate (volume), that is determined by the number of volume cycles (RPM) and the "piping" diameters....It might increase pressure....Not necessarily in a good way...