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Ignition Timing for 1948 Farmall "M" Model


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#1 Ed Estabrook

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Posted 14 February 2008 - 05:03 PM

Greetings All,
I have a '48 "M". It is a gas-powered / 4-cylinder and in stock condition, except for a) it's been converted to a 12-volt charging system, b) I just installed a new electronic ignition (manufactured by Petronix) and c) I have added a ballist resistor in conjunction with a new, standard 12-volt automotive coil. The ballist resistor and the coil now provide the 3 ohms of total resistence in the system recommended for a 4-cylinder engine.

I started her up after the modifications above without any problem. She does, though, have a bit of a "miss" at idle. The "miss" seems to disappear when I get her off idle by adding a bit more throttle. I've never set the timing in the 3 years I've owned her. She seems to idle just fine and I didn't feel a need to change the setting. I have just ordered a service manual. The manual will take a week or two to arrive. In the mean time, can someone tell me what the timing spec. is? I.e, how many degrees before or after TDC at a given RPM should the timing be set to?.
Thanks all.

#2 Michael Halsall

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Posted 17 February 2008 - 03:44 PM

Greetings All,
I have a '48 "M"

I started her up after the modifications above without any problem. She does, though, have a bit of a "miss" at idle. The "miss" seems to disappear when I get her off idle by adding a bit more throttle. I've never set the timing in the 3 years I've owned her. She seems to idle just fine and I didn't feel a need to change the setting. I have just ordered a service manual. The manual will take a week or two to arrive. In the mean time, can someone tell me what the timing spec. is? I.e, how many degrees before or after TDC at a given RPM should the timing be set to?.
Thanks all.


Try this link for basic tune-up info-


http://www.ytmag.com/atrp/specs/ih.htm

Regards from Michael H

#3 CNKS

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Posted 17 February 2008 - 06:45 PM

Greetings All,
I have a '48 "M". It is a gas-powered / 4-cylinder and in stock condition, except for a) it's been converted to a 12-volt charging system, B) I just installed a new electronic ignition (manufactured by Petronix) and c) I have added a ballist resistor in conjunction with a new, standard 12-volt automotive coil. The ballist resistor and the coil now provide the 3 ohms of total resistence in the system recommended for a 4-cylinder engine.

I started her up after the modifications above without any problem. She does, though, have a bit of a "miss" at idle. The "miss" seems to disappear when I get her off idle by adding a bit more throttle. I've never set the timing in the 3 years I've owned her. She seems to idle just fine and I didn't feel a need to change the setting. I have just ordered a service manual. The manual will take a week or two to arrive. In the mean time, can someone tell me what the timing spec. is? I.e, how many degrees before or after TDC at a given RPM should the timing be set to?.
Thanks all.


As the link says, use the first notch. That is static timing with the engine off. Put #1 at TDC, then turn the crank until the pointer and notch match up. If it has a mag, put the coil against the block, then rotate out until the mag trips. Same thing with a distributer -- turn in, then out until you get a spark out of the coil wire. M is not a sophisticated engine, unless you are into modifications for pulling or something you do not need a timing light. Many people time them by ear, rotating the mag or distributer until it runs smooth. Don't advance too far or you will get detonation.

#4 mach-z

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Posted 17 February 2008 - 07:09 PM

Just another way of doing it ! Hook up a timing light with a tach built in . Run the tractor up to full throttle and set the timing to the highest RPM . If you have access to a dyno do this under full load .


You really can't go wrong doing it this way based on the fact that everything is 60 years old and worn. The factory spes were based on it being new , well things have gotten loose over the last 60 years and every tractor will be differnt .

I run a tractor dyno service on the weekends and have seen this many times.

Set it to factory spes and record the RPM off the timing light , then do it my way and see what you get .


You won't have starting troubles when it's warm you won't be advancing the timing that much .

#5 Harold H

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Posted 17 February 2008 - 07:19 PM

In my opinion, you get the best results on tractor engines of this era if you "time by ear".

Harold H

#6 Jalopy

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Posted 17 February 2008 - 07:41 PM

In my opinion, you get the best results on tractor engines of this era if you "time by ear".

Harold H


I agree-

First I make sure the advance is properly working (not stuck and springs good), then I run at about 1/3 throttle and time by ear. I always put them just a tiny snatch retarded. Works for me, I've had good results and never any problems.
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#7 fatjak

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Posted 18 February 2008 - 09:16 AM

:P first of all use a advance timing light so you can see were the timing is at all RPM,s, on the out side of the base of the distribitor you will find harvester part numbers and these can be matched to the harvester or IT&T manuel it will tell you of the advance plate in the distribitor and were to set it i have seen them from 36 to 42.also when ever you bought the hi alt pistons they came with the new plate for the dist and it,s new curve.good luck.

#8 Ed Estabrook

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Posted 19 February 2008 - 09:53 AM

Thanks all for taking the time to respond. Great information.



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