Hey . . listen up. I have said this before . . . The piston position valve timing is old school and was used because no one had feeler gauges in olden days. Our 1913 Cadillac had a marked flywheel with opening and closing positions stamped in the outer surface of the flywheel and it also had a marker arrow for alignment. Henry couldn't do this because he hid the flywheel.
Our Cadillac also had roller tappets but then it was an expensive car made well. But then because it was a very fine automobile it also had a disk brake mounted on the drive shaft with a foot operated pad connected to the clutch pedal which acted as a form of a synchromesh system for easier shifting. Henry used the piston position valve adjustment method because most farmers had a wooden ruler but no feeler gauges. Remember the worn dime used as a spark plug gap adjuster ?
So if you have a worn camshaft that was whittled by hand out of soft iron by boy scouts then by all means use the piston position method to adjust your valves if your block deck has not been resurfaced and you have cast iron pistons. If not then use a feeler gauge.
But just for fun if you have adjustable valve tappets you don't even need a feeler gauge. Every ten degrees of rotation of your wrench is one thousandths of an inch. So turn the engine so the heel is on the tappet surface and turn it down until the tappet locks. Then back-off the wrench 100 degrees to get .010" for the intakes and turn it 90 degrees plus 30 degrees for .012". Then lock the second nut unless you have a self locking nut.
I simply remove the valve cover or covers and push the car backwards and forwards in the garage to get the tappet aligned with the heel. No degree wheel is required. Your cam is in an adjustable position for a full 360 degrees of crank shaft rotation unless it came from Mars. People just love pain and suffering and making things difficult.
Here is the math. Adjustable tappets use a 1/4 28 bolt. These bolts move or advance and retard as they are rotated. 28 rotations of the nut moves the valve stem one inch. One inch divided by 28 equals .035714285714" and so on. I round that out to .036" So every ten degrees of rotation is .001" valve lift. 90 degrees plus ten equals .010". If you don't believe me try it and you will be within .0005" either way if you can rotate 90 degrees plus 10 degrees by ear.
Also since you can adjust a valve anywhere on the heel of the cam lobe you only have to push the car backwards and forwards two revolutions of the engine in high gear to adjust all of the gears since all valves are closed for one full revolution or more of the crank shaft, again unless your car was built on Mars. We have an old saying around here, KISS . . . Keep it simple stupid !
Note: this message was buried in the last post so I repeated it here because I believe it to be both important and time saving.
Very interesting Frank thanks for that info