Farmall Cub

Yessir....Tm Tractor

Item 45
http://www.tmtractor.com/new/el/957fp.htm

I went ahead and replaced both item 45 and 46 ...both plastic washers.

Item 46
http://www.tmtractor.com/new/el/969fp.htm

ScottJ wrote:Not sure I know what you mean. There is no "clicking". I have seen videos on timing with a mag, and certainly noticed the click the mag makes, but mine doesn't have anything like that.

Slowly crank the engine (cutout switch turned off) with a handcrank, do you hear an audible click when the pointer reaches your TDC mark on the crankshaft pulley?

ScottJ wrote:Alright. I can double-check this, but I tried to take care to not budge the point adjustments when I was cleaning it out.

Yes, double check your gap, and check the condition of the points while you are in there.

ScottJ wrote:I had to play around a bit with this to get spark. Does rotor position effect timing? Or does it just have to be at the right place so that the spark can go to the right place?

Yes, the rotor can be reinstalled incorrectly, even 180 degrees off. And yes it will affect timing if incorrect. There is 1 raised mark on the rotor, and it MUST line up with the indicator mark on the rotor pinion. Look closely and you will see the marks we are referencing.

ScottJ wrote:
Excuse my total ignorance on the topic - but if this is using a battery-powered coil for generating spark, why is it still treated like a magneto? Isn't it essentially just a distributor then?

Thanks for all the help!

Just like Eugene said, your magneto should still be treated as a magneto, a previous owner more than likely had the internal magneto coil go out and simply bypassed it with an externally mounted replacement coil. You can always put it back to stock conditions later. I believe the new coils run around $50 each vs. a $10 external coil.

Look at this post, a couple lines down, there is a good picture that shows where the indicator marks are located on the rotor and pinion within your mag.

viewtopic.php?f=1&t=76904&p=617257&hilit=magneto+rotor+marks#p617257

cubguy47 wrote:Look at this post, a couple lines down, there is a good picture that shows where the indicator marks are located on the rotor and pinion within your mag.

viewtopic.php?f=1&t=76904&p=617257&hilit=magneto+rotor+marks#p617257

Awesome! Anything additional to check on gives me hope!

cubguy47 wrote:

ScottJ wrote:Not sure I know what you mean. There is no "clicking". I have seen videos on timing with a mag, and certainly noticed the click the mag makes, but mine doesn't have anything like that.

Slowly crank the engine (cutout switch turned off) with a handcrank, do you hear an audible click when the pointer reaches your TDC mark on the crankshaft pulley?

Nope. There is nothing that clicks like this. The only sound would be the plugs themselves.

cubguy47 wrote:

ScottJ wrote:
Excuse my total ignorance on the topic - but if this is using a battery-powered coil for generating spark, why is it still treated like a magneto? Isn't it essentially just a distributor then?

Thanks for all the help!

Just like Eugene said, your magneto should still be treated as a magneto, a previous owner more than likely had the internal magneto coil go out and simply bypassed it with an externally mounted replacement coil. You can always put it back to stock conditions later. I believe the new coils run around $50 each vs. a $10 external coil.

I'm still confused here, so I took a picture:


You can see that the thing that's supposed to be on top is gone (I still don't know what to call it), and a 12v coil has replaced it. The coil is wired to the battery. Does the same still apply? I thought that the difference between a magneto and a distributor is that a magneto uses physical movement to create spark independant of the battery, while a distributor uses battery power to "charge" a coil which creates the spark. This is why I'm confused why it's still treated as a magneto - what I have seems to be a cobbled distributor system using the magneto assembly.
Thanks for all the help, and sorry for the stupid questions. I'm learning as fast as I can! haha.

ScottJ wrote:Excuse my total ignorance on the topic - but if this is using a battery-powered coil for generating spark, why is it still treated like a magneto? Isn't it essentially just a distributor then?

OK. We are now discussing the hybrid ignition system you currently have. The difference between the two systems, other then where the electricity for the spark comes from is:

The magneto's ignition (spark) advance is an impulse coupling. That's the snap you are suppose to hear when hand cranking the engine. The impulse coupling sets the spark at TDC at engine cranking speed and then goes to full advance at around 250 engine rpms.

The standard battery powered ignition system uses a set of weights and springs to accomplish the advance. The springs and weights set the advance at 0 degrees TDC during engine start up. Then as the engine speeds up, the location of the spark in relationship to the piston being at TDC advances (moves ahead of) (before) TDC.

If the seal isn't good on that replacement cover you may be getting a ton of water into the mag through there. To me you have four choices.

1 - Magneto Route - Pull the magneto off and send it to someone like Rick Spivey to rebuild. (He did mine - Great person to do business with)
2 - Distributor - Buy a distributor and replace the mag......you can probably sell the mag for a few buck to help cover the cost of the distributor.
3 - Leave it the way you have it and replace the mag coil cover and seal not cheap but at least you have a chance of solving the water\rain issue.
4 - Repair what you have - this will probably be the solution that will cause you the most repeated grief in my opinion ...but it will probably be cheap in the short term.

Of course this is just my humble opinion.....

Good luck and keep us posted.

I'm kind of thinking I like #4 for now, and then keep an eye out for a distributor and room in the budget.
Can I just replace the entire assembly with a distributor - or is there something else I have to check for? Is this a pretty straightforward swap?

Again - thanks for all the help.

I personally have never swapped a mag with a distributor but it should be a very straightforward swap when you already have the external coil. But I will let someone else chime in here that has actually replaced the mag so I don't mislead you. To me timing the cub would be a bit different due to the lack of the snap action\sound of the mag.

As far as the help I am simply paying it forward....the people on this site has helped me so very much ........to the point that I now can help others.

ScottJ wrote:Can I just replace the entire assembly with a distributor - or is there something else I have to check for? Is this a pretty straightforward swap?

Yes, expect a good used and complete distributor to run around $80-$100.

The switch over is fairly easy.

Look to purchase an ignition switch also, you would be changing from a single prong to a double prong.

Do you currently have one or two marks on your crankshaft pulley? What year is your cub? Or if you have a serial number handy that works too.

Your current magneto is missing the internal coil and the coil cover that installs over the top. Without seeing the interior, it is hard to tell what else is going on inside.

The fact that you do not hear the audible click at the proper time, I would be concerned with the mag having faulty components within.

ScottJ wrote:Can I just replace the entire assembly with a distributor - or is there something else I have to check for? Is this a pretty straightforward swap?

You will need the distributor and distributor drive housing - a complete unit. Several folks on this board salvage out Cubs, place a wanted add in the for sale/wanted section.

The swap is straight forward. Setting up the distributor is a bit different than a magneto.

Just me, there is nothing wrong with your hybrid ignition system, providing it's in good shape. I would tear it down and fix the problem(s).

The ignition switch Brian mentioned has already been replaced.

If you're powering the magneto with an external coil, the impulse (part that goes "click") isn't necessary.

The way I understand it, at very low RPMs, the impulse works by catching the spinning magnet in the magneto and holding it until just before a piston hits TDC, then it lets it "slingshot" past the coil to generate a hot spark. The magnet is spring-loaded so that it can do this. Once the engine hits a certain RPM, the impulse is disabled because the magnet is spinning fast enough to generate a hot spark without it.

At this point I would get a hair dryer and dry everything out.

Matt Kirsch wrote:If you're powering the magneto with an external coil, the impulse (part that goes "click") isn't necessary.

Incorrect. Impulse coupling is designed to retard the spark to TDC during engine start up. Again, once engine starts and achieves around 250 rpms the impulse coupling drops out and spark advances to about 13 degrees before TDC.

No impulse coupling and the spark is permanently fixed at around 13 degrees before TDC. Meaning, engine won't start unless engine is rotated at over 250 rpms, as in towing the tractor.

if i remember correctly, cub was running fine till it got wet, then he pluued the mag out.
out of time????????????????

So I found something out tonight, maybe you guys can help me decipher it.

I have never timed an engine before, so I may be doing it wrong - but here is the process I am trying for:
1 - Get cylinder #1 to TDC (using a flashlight, and the second notch on my pulley)
2 - Rotate the magneto assembly so my ohm meter shows that the points are closed again
3 - Connect the battery, and rotate my magneto assembly back until I get spark.

I'm stuck on step #2. The points open well before TDC (looks to be just after the 1st notch on the pulley) and so when I'm at TDC the points are already opened and there isn't enough adjustment in the magneto assembly to find that tipping point where the points first open. Am i doing something wrong - or is something not right in my magneto assembly?

Thanks again for all the help! I love learning this stuff, but I'm starting from scratch. A month ago I had no idea that breaker points existed. lol