I actually bought the guage from American Service Center in Arlington VA for $42. It would have to be the first time a dealer has ever marked DOWN an OEM price.
Just to close the loop:
Herr Fuchs told me that a "good" ball stud should compress "only a little" when the cam lobe is rotated down. You measure this with an educated finger between the lower edge of the rocker and the top of the ball stud flange. Feel it with the cam up, rotate, and then with it down. It should barely change.
Here is my procedure for checking. Work from front to rear in order.
- Turn cam lobe up.
- Check preload with tool. If OK do, nothing.
- If not, remove rocker and valve pad.
- Insert good 5.1mm pad and reinstall rocker arm. Rotate cam lobe 360 deg. Let ball stud compress for 2-3 minutes. Estimate difference you will need to bring into spec, and note corresponding pad to order.
- Repeat for all valves.
- Go to dealer (stock item) or web site to order required pads.
- Install and re-measure as above.
Herr Fuchs also told me that it is extremely unusual to go less than 4.75 or more than 5.45. If need a thicker or thinner pad, something else is wrong.
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe