Unstyled A Timing

[jdwalkbehind]

Stumped trying to time a 36 unstyled A. I'm having problems trying to find the sweet spot with a timing light.

To start, everything has been rebuilt and it does run just not as smooth as I'd like. It does however run very smooth under load and it starts just fine. Nothing big/over the top on the rebuild, and yes all timing marks line up (cam to the crank and cam to the governor/with the cam lined up with the governor gear, the coupling on the mag is horizontal, so everything is good that way)

Heres where I'm stumped, with the timing light on the #1 cylinder, the timing light is flashing/showing that it's firing at the bottom of the timing cover on the transmission case instead of at the top where the timing mark is. Thats the highest/most advance I can get it to go for some reason. So by the timing light, it's showing that the timing is very retarted. But it runs and by how far the timing light says the spark is retarded, you wouldn't think it would run.... At first I thought I was off a tooth on the governor, but again as I stated earlier, all timing marks line up.

I know what you're going to say and no, moving the mag does not get me where I need to be, the bottom of the timing plate on the trans is as high/advanced as I can get it to fire (that is by the means of what the timing light is showing)

In my mind, i should be trying to achieve a timing of 15-20 degrees before TDC so that it's starting to ignite the fuel before the piston reaches TDC.

Do I have the wrong thinking here? Or am I not accounting for something? Should I be off a tooth on the governor or is this just how it is/runs? Any help would be great.

 

[RandyB(MI)]

If I'm not mistaken, what you are saying is the light is saying it is firing at bottom of plate instead of up at at the tdc on plate. That would be advanced with flywheel turning CC?? Wouldn't it??

 

[wilamayb]

The early tractors will not run without load as smoothly as the later
model letter series. I blame it on the intake manifold and cylinder
head.

 

[jdwalkbehind]

Yes, sorry I've been trying to wrap my mind around it so much I keep confusing myself. Where I started to go wrong was making my timing marks CW from the impulse line instead of CCW.

I am not able to retard the spark any closer to TDC though. With the mag all the way retarded I'm firing about 30-35 degrees advance. Any thoughts there?

 

[Earl-IL]

Sent email letter.

 

[RandyB(MI)]

I'm sure Earl is going to tell you in detail in his e-mail that the run timing is set by what cup you have in mag and where it is adjusted. Start timing should be TDC , set by mag tilt. Once it's there, leave it alone. Depending on the advance cup in the mag(and it's adjustment) you will probably have 25-30 degrees advance...running. Someone has probably messed with it at some time to get more. Get the mag set at TDC and mark it. That's where it needs to stay. Then take it off and see what you have for timing cup and which way it is adjusted and correct run timing there. Then re-check with light if you want.

 

[Mark-Ia]

If you take the mag off, where are the lag angle marks for the impulse located?

 

[John T]

There's only two timings with the mag. The Start/Impulse which needs to be right at TDC and then the run time advance which happens over around 200 RPM (impulse stops working) depends on the drive cup used and points gap and wear.

Adjusting the mags rear lag and affects ONLY the start/impulse timing.

Turning the mag in the governor affects BOTH start and run timing.

The run time advance timing depends on the drive cup used, the mags position in the governor, points gap and wear and tear.

The start/impulse timing depends on the lag angle and mags position in governor.

I first set the mags lag angle to match what drive cup is used. IE if I have a 25 degree drive cup I set the lag angle for 25 degrees, but if say a 35 degree cup I set the lag angle for 35 degrees. I then install the mag and adjust start/impulse timing to TDC by rotating it Forward CW to retard or backwards CCW to advance. It needs to snap/impulse right when the flywheels Left hand Impulse LHI passes the flat mark at 3 o clock. That's sets the start/impulse where it needs to be. Then I use a timing light to see where she fires aver 200 RPM and if its around 20 to 30 BTDC I let her go. My late friend Duane Larson first set the run time advance and then set the start/impulse (by removing mag and adjusting lag angle) as he wanted the run time advance to be exactly where he thought it needed to be. For gasoline I think 35 BTDC is too fast (I prefer 20 to 25 BTDC) but in the days when they ran low octane tractor drip fuel or distillate 35 was fine. That's why many old all fuel tractors used 35 degree drive cups.

John T

 

[jdwalkbehind]

I've got a long lug Wico X mag that has been gone through completely. Looking at the back of the mag, the phase lag is set at the third timing mark from the left (CW to the left), which I believe is 15 degrees? I was told each timing mark was 5 degrees. Does this sound like its about right where it needs to be?

It does snap/impluse right when the LH impulse mark on the flywheel reaches the timing mark on the cover. So that seems right, but I'm not sure what you mean by matching the phase lag to the drive cup? What are you referring to as the drive cup and how can you tell what degree it is?

I'll check it again with the timing later, but what I'm getting from everyone is I should be aiming for a 25-30 degree advancement in the timing, or that seems to be the norm.

Thanks for the help

 

[440 sixpack]

Get yourself a good RV2B Fairbanks Morse magneto and you will be surprised how much smoother they run.

 

[John T]

For most drive cups the hash mark straight up at the top represents 12 1/2 degrees lag angle and each mark to the left is another 5 degrees of advance. Therefore if you have a 25 degree cup you need a 25 degree lag angle so set the mark 2 1/2 marks to the left. That gives you 12 1/2 + 5 + 5 + 2 1/2 = 25 degrees. HOWEVER if its a 6274 25 degree drive cup, top is 2 1/2 degrees so to get a 25 lag angle you set it 4 1/2 to left.

Lag angle is how much the start time lags the run time and you set it to match the cup, therefore 20 or 25 or 35 etc.

John T