911 Rocker Modification

[rockerarm]

Hey guys, what is the reason for clearancing the underside of the type-4 rocker arm. I have used Gene Berg's elephant feet for years on type-1 engines and do not recall seeing or reading the need on the type-1 rocker arm. Is it for clearance or for ease in setting up the correct geometry. I am guessing this is done whether the 911 style is used or the Courier style is used. Thanks, Bill

[type411]

The type4 rockers are thicker. You just grind the ekstra thicknes away so that they are like the type1 rockers.
It has been common practice for 20-25 years of type4 tuning.

[rockerarm]

type411, So I was out in the garage getting everthing ready to put together another bus engine and after I cleaned up the rocker arms, I decided to measure the thickness where the adjusting screw is and came up with measurements of .515" to .540". To verify my measurements because the venier has had a rough life, I used my metric venier and most of the rockers were measured at 13.5mm, which converts to .530".
I wonder if I can gain an advantage in setting up the valvetrain by "decking" the underside of these type-1 rockers about 2.0mm? I also was eye-balling a set of Scat hi-ratio rocker arms, which measured out at nearly .600", but on these rockers the adjusting screw is on the push rod side. Feedback ?? Thanks, Bill

[Piledriver]

On T4 rockers, the usual amount is 1.5-2mm, you may also find the rocker geometry works out better with a ~1.5-2mm-ish thick shim.
(extra head washers (hardened) usually work great here, as long as they are all exactly the same thickness)

I carved up a set of Chinese 1.4s trying to improve the geometry for Vanagon use, but there's no telling what's needed until you try it.
(I haven't done a T1 in ~25+ years, the vanagon is reasonably close I suppose )

They were buttery soft in the end, so they ended up in the circular file.

Run through the rocker geometry procedure and see what is really needed, it's the only way.

I'd worry about getting the valve side right and then see what the PR side needs.