Timing an M

I want to time my M equipped with a distributor with a timing light. First notch on pulley I understand is TDC. There's two other notches on the pulley. One about a 1/4" from the first notch and the other about 1" from the first notch. I believe it should be timed at 20deg btdc at fast idle. Is 20 deg the notch about 1" away from the TDC notch?

Thanks for your response.

Most M pulleys had 2 marks close together with only one other mark on around for line up of grease fitting in flywheel. M had 40 degree advance. Someone may have made the mark about a inch away when a fire crater kit was installed and the total time limited to 22 degree advance at the crankshaft. Have measurements wrote down somewhere but thinking 22 was around 1-1/8 from TDC mark unless thinking is mixed up with a H pulley. If it's a original M pulley the first of the 2 marks close that gets to pointer with engine turning normal rotation is TDC.

M only had two marks near top dead center from factory. They were the two close together ones. The first one to come around is top dead center and other is five degree after top dead center. Any other marks in the vicinity of top dead center have been added by someone. Original battery ignition systems had a 40 degree advance. No marks were on the pulley to indicate that. When different pistons are installed often times additional marks are made on pulley. If it is equipped with gas head and fire crater pistons, standard altitude, the pulley is supposed to be marked by the installer. That mark is 22 degrees before top dead center and the measurement is 1 7/16 ahead of the tdc mark. I marked many of them over the years.

I have no idea what pistons you have so cannot tell you where to set max timing. What I do when I have no way of determining easily what pistons it has or what advance it has in distributor is to just set static timing at top dead center. Timing lights are useless when you do not know advance of dist as often they will advance some even at slow idle and that is why you set static timing , engine not running.

My own M had 4 inch flat top, gas head , and I converted original distributor from 40 degree advance to 30 degree at full throttle like a super M and the low idle timing runs right close to top dead center.

Was going to look up and double check distance but see Pete 23 has you covered.

This was my Grandad's tractor. He told me when I was a kid it had M&W pistons and bigger valves installed. If that makes no sense, I was too young, didn't understand, and too many years ago!!

Doubt the larger valves, but if M & W pistons, the timing may have been altered. Should have been if it wasn't is about all I can tell you. Would be interesting to see what the total advance of your distributor is though. I for sure would not want more than 30 degrees.

On a little different thing here. You can measure diam of pulley, figure circumforance (spelling wrong) divide by 360 to tell how much each degree would be on that pulley. Called back yard math but it works .

I get along much better when using the "seat of the pants" and "by ear" methods. Never was satisfied with how an H or an M performed when timed according to the book.