I am reading 12v on NEG on ignition coil

M

mrbushhog

Active member
I have no spark( I tried checking using the spark plug out of the cylinder head)
I am reading 12volt on neg side of coil. Is that right?
converted 12volt setup, I did not set this up, so I am figuring things as I go.
Been staring at this cub for years and tired of fighting with it. These things are so simple but all these crap replacement china parts are taking the fun out of it.
 
Sine you say 12 volt, I assume the coil is connected with the negative terminal connected to the side of the distributor. If so, with the ignition turned on you should see 12 volts at the terminal if the ignition points are open. If the points are closed, you should see 0 volts. When an engine stops, the points usually end up closed.

The positive coil terminal should show 12 volts any time the ignition is on.
 
Jim Becker has you covered on the coil function for a 12v neg ground system but looking back at your intro posts (https://farmallcub.com/community/threads/salem-al.112089/) I see your cub is SN 85598 which is a 1949. Is the tractor that you are working on? If so that SN would have had a magneto. You said a 12v conversion so what exactly do you have and what is your objective (goal)? More detailed information will get you more and better answers. JMHO Stan
 
I know exactly what you mean about cheap parts. I once spent a whole weekend fighting with a brand-new condenser that was bad right out of the box. This made chasing down electrical gremlins no fun at all.
The other comment is spot on. Seeing 12 volts on the negative side just means your points are open. When the engine stops, it can stop in any position.
I'd try to turn the engine over by hand just a little bit and watch your meter. The voltage on that negative post should drop to 0 when the points close. If it never drops, then your points might be stuck open, or the little wire going to them could be broken.
Hope you get it sorted out soon!
 
To add one more comment to Jim’s post, if it still shows 12 volt, no matter where the engine stops, it tells you the points are not making contact. File or replace them.
 
Thank you fellows for the quick reply. Lots of information.
The cub was converted to 12v years ago with a small frame alt. Cub has sat for about 3 years because I did not shut off the valve on the sediment bow and all the gas from the tank went through the carb up the manifold into the crankcase. I pushed it into the carport and walked away.
The nice factory IH carb was severely warped when my dad was building the cub and a tube was missing that hangs from the top of the carb by the float. Years later (yesterday) I put a Chinese carb I bought off ebay. Well...later I put gas in the tank and gas pours from the knob on the sediment bowl, (can the valve be rebuilt or do I need to buy another?). And gas was dripping from carb intake.
I started to start engine but nothing, except gas coming from new carb. I started to check for spark, had spark when parked. While having an alligator clip from the spark plug to a ground I engaged the starter but no spark that I saw. Plugs only have a few minutes on them when I replaced years ago.
I will post some pictures as soon as I can to show what I am working with.
Thanks again for the info, just want to drive the tractor not fight with it.
 
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Gary Dotson said:
To add one more comment to Jim’s post, if it still shows 12 volt, no matter where the engine stops, it tells you the points are not making contact. File or replace them.
Click to expand...
I think I know what you mean. Points are not my strong point, still learNing. Heck I don't know if it has points. I thought if it was converted to a external coil that took away the point setup?
 
mrbushhog said:
Well...later I put gas in the tank and gas pours from the knob on the sediment bowl, (can the valve be rebuilt or do I need to buy another?).
Click to expand...
Hi,
Parts of the gas strainer under the gas tank can be fixed.
If it is leaking from the shut off valve handle area, the nut there with the hole through it may just need tightening slightly. There is a packing in the nut. If it is too loose it can leak gas.
Don't overtighten it, it makes the valve hard to turn.
There is a gasket for the glass bowl, it may be old and leaking.
There is supposed to be a screen above the gasket, sometimes they are gone.
Below are listings for them at TM Tractor Parts, you can look at the pictures.
http://www.tmtractor.com/new/fl/426fp.htm

http://www.tmtractor.com/new/fl/235fp.htm

It is easier to get to the gas strainer with the Touch Control arms in the rear, or down position, but your Cub doesn't run.

mrbushhog said:
Heck I don't know if it has points. I thought if it was converted to a external coil that took away the point setup?
Click to expand...
The magneto, and Battery Ignition unit have to have ignition points to run, no matter which coil they have, unless someone has changed it to electronic ignition, which people on here have said doesn't work well with 6 volts.
I think they have said there is only electronic ignition made for the Battery Ignition unit.
The points can corrode when sitting, then no power will go through them, they burn from use too.
File them flat with a point file, or if you remove them, a large flat file. Wipe off all filings with a clean rag. If they are burned much, they need replacing. NAPA has new Cub points, they have said on here.
Below are pictures,
the 1st, from TM Tractor Parts, is a magneto, which all Cubs had up to Cub serial number 115403.
The 2nd is a Battery Ignition unit. Some older Cubs were changed to it.
Nice if we knew which the Cub has.
 

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mrbushhog said:
I think I know what you mean. Points are not my strong point, still learNing. Heck I don't know if it has points. I thought if it was converted to a external coil that took away the point setup?
Click to expand...
Get yourself a copy of Service Manual GSS 1012 and you will have all the info you need to understand how a magneto and battery ignition systems works plus how to service and repair both systems. Just a few more posts and you can access/download it from the Resources link at the top of this page. I can also email you a copy if you send me an email address via DM. JMHO Stan
 
Below are pages from the 1947 Cub owner's manual showing the magneto, and the points and condenser. The points and condenser are under the cover that holds the distributor cap.
It's important that the points have the right gap also, .013" for the magneto.
The cover is held on with 3 screws.
It's better to turn the engine to number 1 cylinder TDC before removing the cover. Don't turn the engine with the cover off, you can lose the timing.
If you need to turn the engine slightly to get the points to fully open, keep track of how you turned the engine, so the cover and rotor are in time with the magneto.
https://farmallcub.club/rudi/farmal...armall Cub Owner's Manual 5-23-47/Page-30.jpg

https://farmallcub.club/rudi/farmal...armall Cub Owner's Manual 5-23-47/Page-31.jpg

Below is a picture of the points and condenser in the magneto.
You need a short screwdriver with a sort of wide blade, to loosen the screw to set the point gap, and an 11/32", I think, open end wrench to remove the points. Use a good light to see in the magneto.
I put a towel on the floor to catch any screws I might drop.
You can use a chair and sit next to the engine, unless there is an implement under the Cub.
 

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This is what I am working with.
Great help with the information! Going to work with it later on tonight.
 

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Glen said:
Below are pages from the 1947 Cub owner's manual showing the magneto, and the points and condenser. The points and condenser are under the cover that holds the distributor cap.
It's important that the points have the right gap also, .013" for the magneto.
The cover is held on with 3 screws.
It's better to turn the engine to number 1 cylinder TDC before removing the cover. Don't turn the engine with the cover off, you can lose the timing.
If you need to turn the engine slightly to get the points to fully open, keep track of how you turned the engine, so the cover and rotor are in time with the magneto.
https://farmallcub.club/rudi/farmallcub.com/rudi_cub/www.cleancomputes.com/Cub/Cub Owner's Manuals/McCormick-Deering Farmall Cub Owner's Manual 5-23-47/Page-30.jpg

https://farmallcub.club/rudi/farmallcub.com/rudi_cub/www.cleancomputes.com/Cub/Cub Owner's Manuals/McCormick-Deering Farmall Cub Owner's Manual 5-23-47/Page-31.jpg

Below is a picture of the points and condenser in the magneto.
You need a short screwdriver with a sort of wide blade, to loosen the screw to set the point gap, and an 11/32", I think, open end wrench to remove the points. Use a good light to see in the magneto.
I put a towel on the floor to catch any screws I might drop.
You can use a chair and sit next to the engine, unless there is an implement under the Cub.
Click to expand...
LOL you got me on the last sentence. One of the issues I have is the belly mower is hooked up and my back is messed up. I would love to be able to sit on something.
 
Thanks for the pictures, it looks like the Cub has a Battery Ignition unit.
Below is info from a manual on here for the Battery Ignition unit, and the points and condenser.
It shows the older original style coil IH used on them for years.
The point gap for the Battery Ignition unit is .020"
https://farmallcub.club/rudi/farmallcub.com/rudi_cub/www.cleancomputes.com/Cub/Cub Optional Equipment Manuals/Battery Ignition Packages for Tractors/Page-11.jpg

https://farmallcub.club/rudi/farmallcub.com/rudi_cub/www.cleancomputes.com/Cub/Cub Optional Equipment Manuals/Battery Ignition Packages for Tractors/Page-12.jpg

The tools I wrote above for adjusting, or removing the points from the magneto are the same for Battery Ignition.
If the breaker cover in the 1st page above is stuck in place, I have found it helps to turn it back and forth in place, to loosen it.
Oil the end of the shaft the rotor goes on, where it says oil in the picture, and work oil into the shaft. That is part of the spark advance, the rotor should turn back and forth slightly. If the shaft gets frozen in place from no oil, the advance won't work right.
When you get it to run, the Cub and LoBoy service manual says to use a timing light to set the timing for Battery Ignition, while the engine is running at slow idle speed, about 500 RPM.
 
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Glen said:
Thanks for the pictures, it looks like the Cub has a Battery Ignition unit.
Below is info from a manual on here for the Battery Ignition unit, and the points and condenser.
It shows the older original style coil IH used on them for years.
The point gap for the Battery Ignition unit is .020"
https://farmallcub.club/rudi/farmallcub.com/rudi_cub/www.cleancomputes.com/Cub/Cub Optional Equipment Manuals/Battery Ignition Packages for Tractors/Page-11.jpg

https://farmallcub.club/rudi/farmallcub.com/rudi_cub/www.cleancomputes.com/Cub/Cub Optional Equipment Manuals/Battery Ignition Packages for Tractors/Page-12.jpg

The tools I wrote above for adjusting, or removing the points from the magneto are the same for Battery Ignition.
If the breaker cover in the 1st page above is stuck in place, I have found it helps to turn it back and forth in place, to loosen it.
Oil the end of the shaft the rotor goes on, where it says oil in the picture, and work oil into the shaft. That is part of the spark advance, the rotor should turn back and forth slightly. If the shaft gets frozen in place from no oil, the advance won't work right.
When you get it to run, the Cub and LoBoy service manual says to use a timing light to set the timing for Battery Ignition, while the engine is running at slow idle speed, about 500 RPM.
Click to expand...
Showing voltage when turning engine over by hand.
Looks like I am going to have to dig into this. Kinda cold around here now and woking in a open shed so it might be a few days before I get to work on it.
 
Hi,
Read Jim B.'s post again, it is number 3 above, and Gary's post, it is number 6, and see if it works like they said.
You didn't say if you filed the points, they should have flat shiny surfaces. Wipe off all filings with a clean rag. The points can corrode when the Cub is sitting.
The original 6 volt system is positive ground.
12 volt systems are usually negative ground, but I don't know what brand of alternator it has.
There may be positive ground alts, but I think they are rare.
 
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staninlowerAL said:
When the ignition switch on what is the reading at the input connection on the side of the distributor with the points closed? Stan
Click to expand...
Yes. And I will add the points are corroded, taking them out tonight. I plan on ordering new ones or going to NAPA here in a few days. Any advice on brands or stores to get a points set from?
 
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