Posted by bloke on February 09, 2004 at 01:14:51:
In Reply to: Re: Re: Re: 20J or 1240 posted by Frank on February 09, 2004 at 00:09:37:
Most don't realize it, and even fewer will admit to it, but not much at all is gained by "short-action" valves.
Many "short-action" valves are quite fast indeed because they are old and a bit loose.
New-fit "short-action" pistons, however - even perfectly lapped and lubricated - don't quite want to travel as fast as normal pistons, as there is significantly more exterior surface area (thus friction) dragging these pistons down.
Argue otherwise, but when newly-rebuilt "short-action" piston sets come back to me with the industry-standard .0005" tolerance, I always am forced to make them looser than this in order for them to go up and down at an acceptable rate of speed.