Engine rebuild 1949 Cub.

[Flyboy]

Stan,
thanks for the invoice. My bolts arrived yesterday. I re-coupled the tractor and the head has been installed.

I decided to check some stuff, so I started with the starter. The tractor came with battery connected to positive ground. I connected the battery with jumpers to the starter and the frame and nothing happened with positive ground. So I reversed the polarity and tried again. The starter engages and rotates with negative ground, so the starter obviously needs negative ground to work.

I tried the same trick with the distributor, and as I connected the jumper to the terminal on the distributor housing, there was a little arc. I don't think that should be happening. When I rotated the engine, there was no spark. I disconnected the battery and called it quits for the night. I need more info and I have to get up at 0400, so it will wait until tomorrow when I get home from work. The distributor looks like this.

[Eugene]

Nothing happened with positive ground. So I reversed the polarity and tried again. The starter engages and rotates with negative ground, so the starter obviously needs negative ground to work.

The starter is a universal motor and rotates in the same direction, no matter the battery polarity. So, some other problem. Probably a solid connection with the cables.

I tried the same trick with the distributor, and as I connected the jumper to the terminal on the distributor housing, there was a little arc. The distributor looks like this.

That thing you call a distributor is a magneto. AND is not powered by the battery. It generates it's own power.

You should not have applied battery voltage to the magneto, thus the arc.

There is an unless. Unless the magneto coil has been disconnected from the points and an external, battery powered coil installed.

[Flyboy]

Ok. So how do I troubleshoot this problem? I was going to disassemble it later today when I get home and take a look at the components within. Any cautions regarding this idea? Are there any serviceable parts within, or is replacement of the entire unit necessary?

[Gary Dotson]

When you applied battery power to the GROUND stud on the side of the magneto, you likely fried the spring on the points. You'll have to open the mag to see. Points & condenser are readily available and are the same as the battery ignition uses.

[Flyboy]

Do any of the manuals online have a diagram of the magneto

[bob in CT]

This is a complete parts manual.

http://www.farmallcub.com/[ Sorry, direct links to manual section is not allowed. ]/download.php?fname=./files/Tractor%20Parts%20Manuals/TC-37F%20Rev%206%208-79%20OCR.pdf

Here is a mag service manual.

http://www.farmallcub.com/[ Sorry, direct links to manual section is not allowed. ]/download.php?fname=./files/Service%20Manuals/Blue%20Ribbon%20Service%20Manuals/GSS-1012%20Electrical%20Equipment%204-27-55.pdf

Both are found above in the pdf manuals section, which is worth a few minutes of browsing so you are familiar with the resource.

A word to the wise on the mag. Parts are expensive and some are only available from donor mags. A special puller is required for complete disassembly or you will damage parts.

[staninlowerAL]

There is an unless. Unless the magneto coil has been disconnected from the points and an external, battery powered coil installed.

If your mag is non-functional and you have an external coil, it works like the later model distributor/battery ignition and can be treated the same except the points gap setting remains .013 instead of .020. If everything else is still 6v then you will need to have a 6v coil. If it is 12v then there are several other changes that need to be made. Bob in CT's post with the GSS1012 reference will give you all the details on how the magneto works. EDIT: To add to Bob's comment about cost, Steiner lists the replacement coil for about $75 and the replacement cap for about $50. Replacing the rotor and pinion gears will take almost another $125. Never seen the replacement magnet listed anywhere.

[Flyboy]

My setup is as pictured above. I am responding to this before reading the manuals that are linked directly above this message. I will be reviewing them momentarily.

I am assuming, based on my very limited knowledge of magnetos, that the terminal on the side of the magneto goes to ground (directly or indirectly) to complete the spark circuit.

Ok, I am back from quickly looking at the link above....editing.

I looked in the banner above for information on the mag, but didn't see any one that caught my eye. Bob, was the link you sent in the "PDFs manuals" link above? If so, which one was it?


My plan now is a limited disassembly to see if I burned up anything by powering the mag, or if there is some other obvious issue with it. I don't have the special tools to do a full disassembly and it looks like I should be able to get to the parts that can be serviced without any special tools.

[Eugene]

I am assuming, based on my very limited knowledge of magnetos, that the terminal on the side of the magneto goes to ground (directly or indirectly) to complete the spark circuit.

The terminal on the side of the magneto is used to kill the spark - shut down the magneto. To run the engine the terminal/magneto is not grounded out. To kill the engine/magneto the terminal is grounded.

The switch on the dash is used to ground out the magneto's spark - shut down the magneto. No battery hook up.

If you decide to operate/run the engine without the kill switch hooked up - have an insulated screwdriver in you pocket. Using the screwdriver, contact the terminal and the magneto base. This will shut down the magneto.

Side note. My grandfather's WC Allis Chalmers magneto has a small metal tag on the terminal. You push in the metal tag to kill the magneto. Get you finger a bit off to the side and your eyeballs get lit up.

[Flyboy]

If you decide to operate/run the engine without the kill switch hooked up - have an insulated screwdriver in you pocket. Using the screwdriver, contact the terminal and the magneto base. This will shut down the magneto.

Side note. My grandfather's WC Allis Chalmers magneto has a small metal tag on the terminal. You push in the metal tag to kill the magneto. Get you finger a bit off to the side and your eyeballs get lit up.

So that is where the expression "bright eyed and bushy tailed" originated?

[Flyboy]

What type of puller is required for disassembly? Is it specific to Farmall's or is it available at auto parts store?

The condenser looked clean and nothing looked burned under the body. Not sure how to test condenser. Looks like a rebuild might be necessary. I haven't been able to open the parts list, but the manual for the magneto opened fine.

[staninlowerAL]

What type of puller is required for disassembly? Is it specific to Farmall's or is it available at auto parts store?

The condenser looked clean and nothing looked burned under the body. Not sure how to test condenser. Looks like a rebuild might be necessary. I haven't been able to open the parts list, but the manual for the magneto opened fine.

I've not done this before, I'm just passing this information along. From a conversation with Rick Spivey: "You will need one special tool, the impulse coupling puller. Earl was making them at one time, I strongly suggest purchasing one. I ruined an pulse coupling plate with a jaw puller, and they don't make those anymore."

[Glen]

Hi,
Here are pages from the Cub parts book showing the magneto. Maybe these pages will work for you, and you can see them. Click on the pics makes them bigger.

http://www.farmallcub.info/manuals/cub_ ... 012-22.jpg

http://www.farmallcub.info/manuals/cub_ ... 012-23.jpg

[bob in CT]

You are jumping WAY ahead. Condensers are cheap, as are points. start with the simple stuff. Then see if you have spark. There are a lot of mags out there working just fine that have not had the impulse coupler pulled in 60 years of service.

[bob in CT]

I haven't been able to open the parts list,

The TC37F manual downloads just fine. I just double-checked it. Try downloading it again as it is a lot easier to have a bookmarked pdf available for reference.