51 jd a

The LHI timing mark at 3 o clock even with the flat mark on tractors side (thats used for timing) is when the left piston is at dead TDC sooooo oo remove the left plug n use a wire etc indicator to determine just when the piston is at TDC and thats when the female slot in the governor shafts end ought to be flat horizontal fore n aft. My guess is the one flywheel punch mark is at TDC while the two marks located above/before (if thats where they indeed are) are is for something like say 20 or 30 degrees BEFORE TDC. If you measure the flywheels outer circumference and divide by 360 you would get degrees per unit inch and perhaps?? those above/before marks work out to where a timing light could be used to measure dynamic run time advance..... ... Anywho, get the left pistion at dead TDC and set the governor so its female drive slot is flat horizontal fore n aft is the bottom line assuming????? the flywheel to crank and cam to crank are all in time.

John T