Checking a coil

[rockfla]

What is OR how is the best way for an "average joe" to check a coil to see IF it is good.......IT is a brand new coil "supposedly" but I need to test it and make sure it works and I don't have a known good coil of this type on hand?? a Ford 9N tractor coil.



Thanks

[Crankster]

General check is to measure ohms resistance of both the primary and secondary windings. This will tell you whether it "should" work. Both ignition coils and condensers are tested at normal operating temperature. Ignition coils are tricky in that a few shorted turns in the secondary winding would be hard to detect but would cause an attenuated spark output. With a new coil though, no need to speculate, you should be in good shape.

[tubman]

Specifically, the primary windings should be in the single digit range, while the secondary windings should be in the upper 4-digit or 5-digit range. These readings are in ohms. If you have a heat gun, you may want to "heat-cycle" it. It will take a while to get it hot enough to fail if it is faulty.

[TravisDM]

Originally Posted by Crankster

General check is to measure ohms resistance of both the primary and secondary windings. This will tell you whether it "should" work. Both ignition coils and condensers are tested at normal operating temperature. Ignition coils are tricky in that a few shorted turns in the secondary winding would be hard to detect but would cause an attenuated spark output. With a new coil though, no need to speculate, you should be in good shape.

I think changing the coil is the best route for my friend's new '52 project. It got idling issue after the previous owner's son replaced the coil he got from a parts yard. We'll take a look soon after we finish installing the shocks and skid plates from 4Wheelonline onto his Wrangler and clear the garage.

[Crankster]

Without specialised test equipment, there's only some rudimentary tests that can be performed. They will weed out the duds, but that's about it. Ignition or high voltage is strange stuff. And as many people have learned "new" parts doesn't necessarily mean "good" parts either. An ignition scope is a very useful tool, takes out the guessing.

[rockfla]

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Here is my dilemma. I have NO spark at the spark plug. I am getting 6.3V to the coil. SO........I pulled the distributor and the points LOOK good. I checked the gap and they are right about .015 to .016, I checked them installed with my VO meter and there is continuity through the distributor from the coil contact to the rotor and stops when the points break SO i know that is functioning correctly. SO down to the condenser and the coil. I have a brand new condenser and for double insurance I have a brand new set of points I am installing today.......SO all that is left is the coil.....ALL items were purchased new in the last couple three years and have NO run time on them at all. Its a fresh rebuilt engine that has sat for a couple of years before any attempts made at starting it. Even with an Optima battery the engine turns slow.....NOT as slow as with a wet cell 6v battery BUT still slow. Even pairing the two (optima & wet cell) it spins slower than I would like.....could that effect spark?

[marko39]

Did you check voltage to coil while cranking engine? Sometimes starter will draw too much not leaving enough for coil.

[rockfla]

Originally Posted by marko39

Did you check voltage to coil while cranking engine? Sometimes starter will draw too much not leaving enough for coil.

No Sir, I will do that tonight and see, thank you for the suggestion.


so Question: Can you use a "direct" jumper wire from an external battery to the coil during the starting process to combat this issue??

[tubman]

I always thought the starter on my '51 didn't spin fast enough, even though it always started the car. Last summer, I decided to check it out. I replaced it with a spare I had, and it really made a difference. I found a cold solder joint in one of the brush sets in the original.

[rockfla]

Originally Posted by tubman

I always thought the starter on my '51 didn't spin fast enough, even though it always started the car. Last summer, I decided to check it out. I replaced it with a spare I had, and it really made a difference. I found a cold solder joint in one of the brush sets in the original.

I question the starter as well, its a new starter sold by Ford Tractor guys SO I think they are most likely "Chinese" made. NOT real confident in it that is for sure!!! The ground strap from the battery to the body sure gets hot!!!!! SO I'm not sure getting another starter is more than a crap shoot at best?? I thought about doubling the ground strap battery cable IT that would possibly help?

[tubman]

When I was having my starter problems last summer, my first solution was a rebuilt from NAPA. That one was much worse than the one it replaced. At least it showed that the problem was the starter. A venture through the back of one of my many disorganized parts shelves yielded a very clean unit with a tag on it that said : "$10 - Good". Installing that one solved my problem. The rebuilt went back to NAPA for full credit. I guess "Rebuilt does not equal good" is true as well.

[rockfla]

Tubman
After talking to my Dad he made sure this starter he got was a "Ford" starter and NOT an import one....NOW with that said IF its a reman then the age old question....Where are the internal parts from??? Again the motor is "FRESH" rebuilt SO I am banking on it being "tight" from new as to why the starter drags.....I think IF i can get spark it's fast enough that it will start. I just got to ferret out why I have NO spark.

[rotorwrench]

I've been operating a Ford 850 of 1956 vintage for a while. It has the flathead style distributor rotor that required a metal clip to make it drive properly. They can fall off undetected and a person has to dig around in the dirt with a magnet to find it. I keep a number of those clips around now just in case I lose one. I'd say check that first. If you want to check just the coil, set your coil wire from the tower terminal up close to the frame somewhere with a shared ground path to the electrical system at large. Take a screw driver or a non-metallic probe of some kind with a well insulated handle and open the points with the ignition on. As long as the screw driver tip isn't grounded to anything, it should spark any time the points are opened as long as the condenser is still good. Don't leave the power on to the coil too long with the points closed or it can overheat and damage the windings.

If your ground strap gets warm while operating the starter, that's not all that abnormal since it takes a lot of amps to turn the starter motor. Just make sure you have a large gauge ground and power cables if the tractor is still 6-volts. 12-volts can work OK with the smaller cables but 6-volt needs around 2 gauge cable minimum. Larger cable is even better. If the starter is turning without excessive drag then it's likely OK but may need new bushings & brushes as some point.

[Crankster]

Couple things just from a quick take - New condensers are notorious for being defective, and will dependably cause trouble. I would suspect that, at least before condemning the ignition coil. Points can get a layer of almost invisible scrunge on them practically overnight and prevent continuity to ground, check continuity from the movable arm to the points plate when closed as well? A light dressing with a point file.

Also check the overall resistance from negative or battery ground post to the distributor points plate, this needs a resistance not to exceed 0.2 ohms. The distributor needs a good electrical contack with block. A jumper wire or cable from housing to battery ground is an easy test.

I like to use a shop manual troubleshooting guide, because I don't understand all that stuff, and it works through the tests in a logical, step by step method to isolate and eliminate the problem.

Cables should not ordinarily be getting hot, that could indicate loose or corroded connections, or undersized cables, or maybe a defective starter? Generic replacement battery cables are also notoriously bad, esp. for 6 volt systems.

Defects in the starter or starting circuit could most definitely cause an ignition problem because that will result in excessive current being drawn exactly when needed for spark at the plugs. Maybe could try removing the spark plugs and see (should spin faster) if there is a good spark from the coil wire terminal to ground. This will isolate or bypass any trouble in the rotor or distributor or plug wires, plugs, etc.

[rockfla]

Thanks for the heads up Rotorwrench although its not a 9N tractor "per se' ". Its our "proto type" Ford GP jeep......which basically is the 9n Motor......the original distributor set up is quite unique and rare SO the next method is using the 9N distributor and coil. SO that is were the "tractor" part comes in. These GP's were notorious for "ground" problems, originally only two grounds, one from the battery to the body, one from the body to the frame, both with the flat braided strap. I am planning on adding another ground from the starter mounting bolt/engine to the frame. and another ground on the other side from body to frame again. Rotorwrench, crankster, thanks for all of the 411, I will work my way through all you have suggested and let you know.

[rotorwrench]

The 9N was set up with the front mounted distributor as were the early 8N tractors. 2N wartime tractors came with a magneto. The Ford GP was the only one to have the 9N style engine but was under powered. The War Department wanted them standardized so the GPW was built using the Willys design so that there would be standardization between the two manufacturers. The GP was manufactured in limited numbers due to the standardization move and they started out with the angle drive set up if I remember correctly. Parts are hard to find for those but they did made a lot more for spares so they should still be out there but expensive. The series 1 had the angle mount but I think the series 2 has a straight mount type. They did some weird things trying to make that stuff work before standardization came about. I haven't seen a good photos of those set ups so I don't know whether adaptation can be done or not

Ford also used the 9N in some 1941 pickups but they were so under powered that the sales were dismal on them. They used the front mount set up like the tractor with the coil mounted to the top. The coils require the same resistor used on the passenger cars & trucks of the era.

The coil could still be checked but a person may have to use a conventional Ford type distributor and a ballast as used in 1941 for the power feed to the coil. Jumper leads could be used to set it up and a spark plug direct to the coil primary terminal with a ground jumper to observe the spark.

The flat braided straps, in good condition, should carry the amps needed. There are different size straps available for different applications if a person wanted a larger one or had doubt about its function.

[rockfla]

Rotorwrench
Looking at "Yesterdays Ford Tractor Parts" and I see the rotor but don't see the "clip" you speak of?? The rotor on my distributor is indexed with one flat side so can only go on one way and seemed to be to somewhat snap onto the shaft?? NO??
Yes you are correct on the "original" set-up's. I have "most" all of the pieces BUT I am missing the vacuum advance on my distributor (Pic #3). Mike at Third Gen has it, seeing IF he can build it for me, I think a 49-53 Advance can be adapted to work. AND "NO" even though some "extras" where made for the "after market" they are still "extremely" difficult to find!!! AND YES very expensive......the bigger issue IS the "drive gears".....three specialty gear shops have passed on making them!!!!! The ONLY part harder to get and WAY more expensive is the carburetor!!!!

[rotorwrench]

It may not have used the clip. Most of the applications that used it had the large rotor as was used on crab type and some later Load-O-Matic type distributors.

The driven end looks a lot like the same or similar pattern to the 9N type distributor. The 9N has similarities to the crab type distributor and has mechanical advance but no vacuum brake. The GP had a vacuum advance can but I don't know if it has a Load-O- Matic system or a set of flyweights with vacuum retard. It looks like a Load-O-Matic. The LOM works OK for small motors like that one. The vacuum can looks like the later LOM type anyway.

Thanks for those photos. Questions come up on these now and then and those help a good bit.

[rockfla]

Here are more of the distributor IF it helps AGAIN NO vacuum advance. I can post more pictures of the drive housing and gears IF you like?

[drolston]

Originally Posted by rockfla

No Sir, I will do that tonight and see, thank you for the suggestion.


so Question: Can you use a "direct" jumper wire from an external battery to the coil during the starting process to combat this issue??

Slow cranking on a fresh battery probably means too much current draw by the starter, which will definitely reduce voltage at the coil when you need it the most. I once had a flathead that would not fire when cranking, but would fire the instant I let go of the starter button, while the flywheel still turned the engine for a little bit.