Swivel Foot Adjusters Revisited

[seventythree]

I looked through the archives and followed some threads regarding swivel foot adjusters. As a result, I decided to go with the 911 variety. The general consensus throughout the posts was to remove 0.060” from the bottom of the adjustment end of the rocker to make room for the swivel foot. Well, here are my findings after going through the process myself:
1) I mocked up using the stock adjuster and set the lash to .008” for the exhaust valve. Then I measured the distance from the bottom of the adjuster to the top of the rocker, where the lock nut rests, to be .645”. Then I removed the rocker, installed the swivel foot on it, adjusted it such that the foot could swivel fully, and measured the distance from the bottom of the swivel foot to the top of the rocker to be .800”. As a result, I realized that the actual amount of material to be removed from the rocker was .155” as opposed to .060”!

2) With that much material to remove, I decided that counter-boring the screw hole was a safer approach than milling the material off. The swivel foot measured .390" in diameter, so I figured a .500" counter bore would provide adequate room for the swivel.

3) I was smart enough to decide to use a friend’s mill and not attempt this with a hand drill and a vise, or even a drill press for that matter. The rocker material is way too hard for high-speed cutting tools. The high-speed drill I started out with barely put a scratch on the first rocker before it was toast. So, I bought a Carbide-tip drill and even that was toast by the time I was done with rocker #8, and I was using plenty of oil for cooling.

4) The reason I charged-on this far before asking is that with the .150" counter-bore there is still enough thread left (.350") to go back to the stock adjusters with no harm done. But, with the unthreaded swivel portion of the 911 adjuster being so long, only ~.200" of thread engagement will remain.

Now, the $3000 question is, is that enough?

[Dave at Pelican Parts]

I don't know if that's enough or not--but the method used by the more careful builders seems to be:

1) Take 0.060" off the face of the rocker arm that is toward the valve tip.
2) Shim the rocker stand. I think the amount is similar, about 1/16" or so.
3) Fabricate custom-lentgh pushrod so valve train geometry is correct.

You want the solid part of the adjuster to be parallel to the valve stem when the valve is halfway from closed to open. This avoids putting unnecessary side loads on the valve stems, and results in normal valve guide life. Supposedly if you set this up too far wrong, the valve guides will get loose before their time and you'll be replacing them relatively frequently.

No personal experience with this, just passing on what I have read.

--DD