Help! Fordson N magnetos

[J5TPT]

I have a 1942 Standard Fordson that is fitted with an Lucas SR4 magneto.

The tractor has always started and run well on this magneto however it has recently started to misfire when hot and I suspect that the condenser is on its way out.

I have a Lucas RF4 magneto that I would like to fit in place of the SR4 but despite the RF4 being in excellent condition (just come off another running tractor) and having a good spark etc, I cannot get the tractor to fire on it at all. When I put the SR4 back on, with the same leads and plugs etc, the tractor starts first time.

The RF4 advance and retard is fitted correctly (not on stop) and I have tried starting with it in various positions, as well as the start position, but can't get the engine to even cough.

Other than being fitted with a later E27n manifold, the tractor is standard.

I seem to recal hearing of someone having this problem in the past.

I would very much appreciate any advice that anyone could give.

Is it possible that the RF4 is timed differently to the SR4? I find this unlikely but can't think of anything else.

[Dandy Dave]

It is easy enough to check any impulse mag on any tractor for timing. As you crank it over slowly it should click at Top Dead center, or a little before. If not, the mag internals are a little different and the mag will need to be timed to the engine via the coupling adjustments. Also, some mags are set up to turn Clock wise rotation, some are set up to turn counter clockwise. If the mag is off of the same make of tractor, it should have the same rotation. Pull out number one plug. Feel the compression, and watch to see if the plug sparks at the top of the compression stroke when it impluses. You may even be 180 off if you did not set it up on the compression stroke to begin with. These old Fordsons fire 1-2-4-3 if my memory serves me correctly. From the front of the tractor looking rearward the mag should be turning clock wise on an E27N. The rotor in the mag will be turning counter clockwize. Most mags, #1 is the top outer lug. Below that is #2 Inside on the way up will be #4 and then inside top will be #3. Think about it and study it and you will beable to time any tractor with just a little common mechcanical knowlege. If you do not see a spark at TDC #1, take the mag off. Put it in a vice and rotate the coupling with a pair of locking pliers until you see a spark at #1 post when the mag impluses. Turn it back a little until just before the points open. This is where the mag will be set to fire. Spin the engine until it is on TDC #1 compression stroke and put the mag in in the position. If things do not line up, within a few degrees, the coupling will need to adjusted. If adjustment is not easily obtained, then you will need to fix the original mag. Dandy Dave!

[J5TPT]

Thanks for the advice.
I will check as you say.
The RF4 has come off a 1934 waterwasher and mine is a 1934 which, I would have said was basicaly the same tractor, so it just seems rather strange that the SR4 should run so well and the RF4 doesn't want to run at all.

[Dandy Dave]

And you are working on an "N" then. The "N' and "E27N" timing are pretty much the same as timing goes. The earlier "F" is a different animal, as the timer runs off of the cam shaft and turns counter clockwise. Another discussion for another day. Dandy Dave!

[J5TPT]

Sorry, should have said that mine is a 1942 not a 1934.
Both N's though.

[CalGG]

My E27n is fitted with the RF4 magneto

When using the electric self starter, the impulse coupling fails to kick after the first full turn of the crank shaft. The engine just spins to quickly, and the imulse dogs move out due to rotation.

All the years of living with this tractor, I have only used the hand starter until this year, when the fitting of a snow plow mount fouled the hand crank. So there has not been any troubles till recently.

How I get around this little difficulty? First, as mentioned, listen for the click. IF it's not heard, release the starter button, let the crankshaft stop turning, then again reengage the starter. I have gotten used to just jogging the starter allowing the impulse coupling to hit on the first pass. Seems to work just fine.

I suppose the next time I'm into the mag I could fit some springs to hold the fly weights in until the engine was really running. That would seem the best all around.

Cheers

Cal

[Emiel]

Hi,

I think I recognize the problem.

We used to have an Allis B which ran perfectly, but leaked oil on the magneto flange. Replaced that part and then the tractor wouldn't run anymore. Timing was correct, tested several times.

After stripping almost halve the engine, a friend of ours found the magneto to be 360 degrees out. Also, spark on tdc with opened exhaust valve.

I found correct timing on the E27N quite easily. put a screwdriver in the first spark plug hole and watch it move. Then you'll find oud the piston position, found out whether it is compression or exhaust. Turn one rev over to compression if necessary and put the magneto in spark position and fit it.

Then this should be ok.

Rgds

Emiel