1951 JD A distributor timing question

I will installing new points and condenser in my 1951 JD A with distributor. I have an OM that shows how to do it removing sparky plug on the flywheel side, removing the side flywheel cover and lining up the mark on the flywheel and flywheel cover. With the ignition on you turn the distributor until the points open. Here's my question: Would it be possible to use a timing light with engine running and point the light at the flywheel cover mark and the mark on the flywheel to line them up? Just a thought I had. If anyone has an easier way, please share. Any assistance is always appreciated.

That would be fine. Remove the center section of the flywheel cover. There is a dot on the flywheel and a vertical slash mark on the flywheel cover in the 6 o'clock position. Idle the tractor as slow as it will go and adjust the distributor until the dot aligns with the vertical slash. Now speed the tractor to wide open throttle and the dot should move clockwise to about the 7 o'clock position.

I tried it with a timing light once but got better results with the manual method. If it's running you can't be sure there's no advance and you end up with late running timing.

Steve,

A) It will help if you understand the basics of static start timing and advanced run timing. At extreme slow cranking speeds while starting, the plug fires close to TDC, and its when the points break open that the plug fires. HOWEVER once up n running the spark timing advances to BEFORE Top Dead Center (BTDC) and typically SUBJECT TO RPM AND THE ADVANCE CURVE it may be as high as 20 Degrees, more or less, BTDC for the most efficiency. Sooooooo if (not running of course) the flywheel is set so the left piston is right at TDC and you rotate the distributor just till the points break open, that is when the plug would fire. Once running the timing will advance as RPM increases so the spark will eventually fire BTDC. True a timing light flashes when there's a spark regardless if its firing at TDC or 20 BTDC so use as you can and like, just remember when she's not running there's no advance happening. A timing light can also be used to see how and where the plug fires as RPM increases, so you can rotate the distributor to adjust the timing at X degrees BTDC at X RPM as called for. Just be aware when she's not running (or very slowly cranking over) the plug wont be firing near as much BTDC as it will once up to speed.

B) NOW TO YOUR SPECIFIC QUESTION

"Would it be possible to use a timing light with engine running and point the light at the flywheel cover mark and the mark on the flywheel to line them up?"

The problem I see with that is when you say "WITH ENGINE RUNNING" because as I described above, when the engine is running the plug will NOT fire at TDC but quite a bit BEFORE THEN. A timing light can still flash at extreme slow cranking over speed and that's when she needs to fire near TDC so it can possibly be used BUT THAT ISNT WHERE SHE FIRES WHEN RUNNING (MORE LIKE 20 BTDC THEN)

C) When the manual describes how to rotate time the distributor so the points break open at TDC, that has to do with static start timing and its only after that and she's up n running at RPM she advance times at say 20 BTDC

John T

Likewise, I preferred the manual method to set the initial static start timing so she fired near TDC while slowly cranking and then used a timing light to see if she fired at X degrees BTDC at X RPM and if it was close I left her alone. In the alternate, however, a person could start her up (if it starts) and use a timing light to set it for X degrees advance at X RPM and then if she started fine again, leave her alone............

John T

If you have a timing light that you can program for the amount of advance that you want then a light will work. I set the degrees of advance 20 in the light and then line up the zero mark with the light and you are all set.

Sounds like a good plan ET. In other words IFFFFFFFFF you have one of those neat programmable timing lights and set it at 20 degrees BTDC then you can "WITH ENGINE RUNNING" (like the poster asked) adjust timing so the light flashes at the TDC marks. Otherwise, of course, "with engine running" a normal non programmable timing light isn't gonna flash at the TDC marks because by then the timing has advanced faster then that.

I still remember meeting you at The New York Two Cylinder Expo

John T

We still do the Friday get together's that you started.

Great, but without me lol now that were HOMELESS (sold the farm) and full time in the RV maybe I can make it up there again.

John T

You don't need an expensive programmable timing light. Use a simple protractor to make a chalk mark 20 degrees clockwise of the vertical slash which is the 6 o'clock position. You should end up at around the 7 o'clock position.

That's right my friend Erskine aka Tom 43 aka Barack, I just used a regular light and do it as the owners manual indicates and NEVER had a problem. It would be neat however to have a programmable unit like ET does with no need to mess with a protractor and chalk mark. To each their own

Hope all is well your way

John T