In a message dated 10/22/03 12:12:01 PM Pacific Daylight Time, [email protected] writes:
> The shims are there to get the valve train geometry right. The "right" way > to do it is to make custom pushrods the right length, but shims under the > rocker stands will work within limits. ------------------------------------------------------------------ On the VW engine the valves are at an angle of 9.5 degrees. Depending on the ratio of the rocker and the lift of the cam, to achieve proper valve train geometry on a VW you may have to adjust both the tower height, the rocker arm position (vertically) and the push-rod length, which provides maximum transmission of lift 'around the corner' at only ONE particular length. This is easy to illustrate in a classroom... or with lots of charts -- but difficult to get across via email without getting into trig The shims you found on the old heads are going to be relative to the length of the valves and the wear (if any) of your rockers, plus the assumption that you're using the same type of adjusters. The length of the push-rods is going to be relative to all of the ABOVE plus the width of the engine (actually, the distance from the centerline of the camshaft to the centerline of EACH rocker-shaft [so don't get the banks mixed up; they could be of different length]. All of which assumes your new heads are identical to your old heads, right down to the freckles on their fanny. If not, you gotta start over again, set up the valve train geometry from scratch. Or do like most engine builders and simply ignore it. No big deal. Get your valve train geometry wrong you only give away up to 20% of your power. :-) (Chorus: 'THAT CAN'T BE RIGHT! THAT CAN'T BE RIGHT!' ) (From the Conventional Wisdom Opera, Act II) -R.S.Hoover PS - Actually, a 20% hit would be the Worse-Case. But the typical dune buggy engine gives away a solid 10% of its potential output. There's even room for improvement in a crate engine from the Puebla plant, thanks to the normal manufacturing tolerances. Find a Formula V race-engine builder, rattle his cage, get ready to be impressed with some serious attention to detail.
