Humble opinion:
1. Mr. Vince Falter, in his Ford Barn centrifugal advanced Model B distributor article, mentions that the 15 degree initial crankshaft timing advance mentioned in Ford's March, April, & May 1933 article appeared to be an error & it should be 19 crankshaft degrees.
2. If one carefully measures the timing pin locations on a Model A timing cover vs. a Model B timing cover, one can clearly "experience" & actually "see" where the Model B timing pin is located 9-1/2 degrees BTDC (1/2 of 19 crankshaft degrees), on the timing gear cover as opposed the Ford mentioned 7-1/2 degrees BTDC, (1/2 of 15 crankshaft degrees as initial timing.
3. This means that when measured on the timing pin location circumferences, (with the center of this circle centered on the center of the timing gear), that the Model B timing pin at 9-1/2 degrees advanced is roughly 7/16" higher or further advanced than that of the Model A timing pin.
4. Mr. Falter also further "experiences" clamping the distributor's shaft in a vise, then rotates & advances the spring loaded centrifugal device on top to find that the rotation of the centrifugal advance Model B distributor advances a maximum of 8-1/2 degrees.
5. It may sound confusing to hear engine people mention the different crank degrees, crankshaft degrees, timing gear degrees, valve timing, ignition timing, distributor advance degrees; however, it is important to realize first that here in the U.S. all complete circles or one complete revolution will always have 360 degrees whether on a crankshaft, timing gear, or distributor.
6. Next, the crankshaft gear is 1/2 diameter of the timing gear; hence, when the crankshaft turns one revolution, (360 degrees), the timing gear & distributor turn 1/2 revolution or 180 degrees; hence the timing gear & distributor are always turning twice as fast, (double the rpms), as that of the crankshaft.
7. Then remember that this entire discussion is about the number one (1) spark plug firing at so many "crankshaft" degrees BTDC known as "ignition timing"; however, we are measuring "timing" on a timing gear & distributor that is turning twice as fast as the crankshaft.
8. Good thing engineers don't write cook books ....... we would all be eating grass because nobody could understand what they were trying to explain in the first place.
9. Anyway what Mr. Falter further explains is that because ignition timing degrees amounts are based on crankshaft revolution rpms which are twice that of distributor revolution rpms, his 8-1/2 degree distributor advance translates into 17 crankshaft degrees & when added to the initial Model B 19 crankshaft degrees, the Model B theoretically could advance at higher speeds to near 36 crankshaft degrees BTDC.
10. Even though the Model A was designed with an initial timing of 0 crankshaft degrees BTDC, & to advance to 40 crankshaft degrees BTDC, it was recommend to run with spark lever only 1/3 to 1/2 way down after starting which he tested to be about 13 - 20 crankshaft degrees BTDC. (Makes sense with lower Model A head compression).
11. The Model B came with a crank & when timing is correctly set at 19 "crankshaft" degrees BTDC, I have never witnessed the engine kicking back with a hand crank or starter.
12. However, if one buys one of these timing devices with curved degree markings near the crankshaft pulley, & mounted on the flywheel cover, if one sets the crankshaft timing at the 19 degree mark on this device & decides to crank the engine, with a Model b distributor .......................... please dial 911 first & notify the ambulance to bring an arm sling & trauma medication -- the engine will kick ferociously -- with these timing devices, the verified TDC mark on the crankshaft pulley has to be set at 9-1/2 degrees BTDC for correct "ignition" timing.
13. I was always advise not to allow a Model B distributor advance more than about 28 degrees at about 2700 rpm.
Hope this helps, especially if someone cranks an engine with a Model B distributor.
