851 Ignition Oddity

[ole fred]

I bought an 851 from a friend who bought it from a church. It is a nice one that has been converted to 12 volt with a 10SI. My friend didn't realize it didn't have power steering and live PTO, so I ended up with it.

So, I always had trouble starting it, but it ran fine once started. It would crank for a while with nothing and then when you release the starter button, it would start. No problem, I just learned to not crank long. Just hit the button and it was running. Then, it got to where it wouldn't start at all. If I put a charger on the battery, all was good. It had a 6 volt coil with a resistor of unknown resistance. The battery was getting weak. The resister had two coils side by side, but only one was being used. The spark was weak. I didn't check the resistance, but am sure it has to much resistance. Now, I put a small jumper wire on one end of the resister and when I start it, I just bypass the resister and it starts fine. I then unhook the wire.. So, when cranking with a weak battery, the voltage supplied to the coil wasn't enough to get a good spark, but when you released the starter button, the engine coasted enough (they really crank fast) with full voltage to start. Makes sense to me. Of course, now with the cold weather it won't start and will barely crank. No biggie, I don't use it now anyway.
This brings up the resistor bypass circuit on a lot of Delco systems. My MF TLB gasser has one and it will start anytime. There is nothing like shooting 12 volts to a 6 volt coil to make a hot spark. I don't know why they didn't put that on everything - back in the day at least.
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[Sean in PA]

It sounds like it might not be getting power to the coil when the key is in the Start position, only when it's in the run position. You should be able to run a small wire from the large stud on the starter side of the solenoid directly to the hot side of the coil so that the coil receives power when the key is in the Start position, and it will bypass the resistor to provide a hotter spark while starting. Once it starts and the key drops back to the Run position, the solenoid opens and it will provide the power to the coil through the resistor.

 

[john in la]

Sean
I didn’t read where he has a key with start position.
Running a wire from the starter side of the solenoid to the coil will work when cranking but it will allow for a spot for the wire to back feed the starter while running causing a weak spark.

Delco does have a resistor bypass system but it doesn’t work with the ground starter button on the transmission.

I would say let’s get a known good battery in the tractor with clean tight connections at every wire end and then we can go from there.

 

[Duner Wi]

12 volt GM products starting in the 50s supplied 12 volt while starting. I think you could run a wire from starter to coil with a diode inline so no back feed.

 

[ole fred]

Boy, you guys are quick. Yes, a good battery fully charged will start it with the present resistor. A correct resistor will fix it also, Still, it works fine with the jumper wire bypassing the resistor.

The key switch is fine. It is either on or off. No start position.

Agreed, you can't use the resistor bypass solenoid on the Ford grounding system.

What resistor would be correct - ohm wise?

 

[john in la]

What resistor would be correct - ohm wise?

A 6 volt system typically has a 1.5 ohm coil give or take a little.
A 12 volt system usually has a 3.0 ohm coil give or take a little.
So a 1.5 ohm resistor is what you are looking for give or take a little.
You want your coil and the resistor to add to about 3.0 ohms with the 12 volt conversion.

 

[Btzj02]

I just have to ask, can you tell by the wiring what is the purpose of the resistor? You say it was converted to 12 volt so does the resistor only affect the ignition coil or does the resistor affect the whole electrical system? Either way my preference is to install a 12 volt coil and wire it with no resistor in series. If the rest of the tractor is still 6 volts you of course will need a resistor as "john in la states". An ideal 12 volt conversion, in my mind, is to convert everything to 12 volts and eliminate all resistors but that is a personal preference.

 

[ole fred]

The resistor is only wired to the coil. I really like the idea of using a 6 volt coil and resistor with a resistor bypass circuit.

 

[da.bees]

I much prefer 6 volt coil w/separate resistor with 12 volt system. Reason being that 60 year old tractors usually has worn components along with voltage drop. By-passing resister during crank assures hot spark even with less than fully charged battery. I replace daily driver batteries before they go bad and old battery is put on an old tractor or other non-critical application. Something like an old group 65 battery that no longer puts out enough amps to start a diesel truck still has more than enough cranking amps for a low compression 200 cu gasoline engine.

 

[john in la]

If the rest of the tractor is still 6 volts you of course will need a resistor as "john in la states"

What part of anything I said give you that idea.

 

[Btzj02]

If the rest of the tractor is still 6 volts you of course will need a resistor as "john in la states"

What part of anything I said give you that idea.

If all of the original 6 volt equipment is retained and the battery and alternator/generator are converted to 12 volts then the comment: "So a 1.5 ohm resistor is what you are looking for give or take a little." Applies to the whole tractor not just the ignition. Of course if all light bulbs, gages and such have been converted to 12 volts then it only applies to the ignition circuit. Didn't feel I needed to rewrite what you had already covered. I think "ole fred" got what I was getting at and he has a plan for his tractor.

 

[ole fred]

I really like the idea of using a 6 volt coil with a resistor and running a wire with a diode from the starter to prevent the coil voltage from back feeding to the starter when running. This is to bypass the resistor and is with a 12 volt conversion on the 6 volt Ford tractor.
Question: Where can a fellow buy such a diode? I have a bunch of them available from my old stack of Delco 10 DN's, but they aren't particularly suitable for such an installation.

 

[Duner Wi]

Ebay has them for not much money. 10 for less than $10.00 delivered.
1N5402 should work. 2 in parallel would surely work.

 

[ole fred]

Thanks

 

[Btzj02]

Thanks

I have extras that I believe will work. I'll mail a couple to you gratis if you send me a snail mail address to my email.

 

[ole fred]

I have extras that I believe will work. I'll mail a couple to you gratis if you send me a snail mail address to my email.

Thanks for the offer, that's gentleman of you. If I got them, I would probably loose them before I got around to using them. The tractor is buried in the back of the pole barn now and won't be out until at least spring. The jumper wire works good enough for now.
Thanks again
Fred

 

[da.bees]

If memory serves me correctly, Ford tractors and cars of the period had 2 small screw terminals on solenoid. One marked I= ignition while cranking and S= starter. While starter is running the I terminal is by-passing resistor to coil. Tractor and car solenoids look similar but S terminal on car requires 12 volts and tractor requires ground. Over the years (and presently) car solenoids are easy to find, tractor version not so easy. A popular hack is to add push button on dash to send 12 volts to car solenoid being used on tractor. No diode to prevent back-feed required for either. Kiekhaefer Mercury outboards were popular at that time and used same solenoid as cars. Only difference was that boxs containing solenoids for outboards cost 3x as much as those for cars.

 

[Duner Wi]

If memory serves me correctly, Ford tractors and cars of the period had 2 small screw terminals on solenoid. One marked I= ignition while cranking and S= starter. While starter is running the I terminal is by-passing resistor to coil. Tractor and car solenoids look similar but S terminal on car requires 12 volts and tractor requires ground. Over the years (and presently) car solenoids are easy to find, tractor version not so easy. A popular hack is to add push button on dash to send 12 volts to car solenoid being used on tractor. No diode to prevent back-feed required for either. Kiekhaefer Mercury outboards were popular at that time and used same solenoid as cars. Only difference was that boxs containing solenoids for outboards cost 3x as much as those for cars.

What you mentioned is the way I did my rewrite on skid loader. You do need a 12 volt solenoid such as 56: Ford pick up cand a push button switch that supplies battery voltage to solenoid. For me this would be preferred over a wire from starter bypassing the resister. The diode would be less costly and a little easier to implement.

 

[ole fred]

What both of you mention would bypass the neutral start safety system. Ford grounds the second terminal of the solenoid and feeds 12 volts to the other small terminal when the ignition switch is turned on.

 

[used red MN]

If all of the original 6 volt equipment is retained and the battery and alternator/generator are converted to 12 volts then the comment: "So a 1.5 ohm resistor is what you are looking for give or take a little." Applies to the whole tractor not just the ignition.

Why have you put this “mumbo jumbo” into a reply here? Now someone down the road is going to want to know how this is done. Someone will have to tell them they need a big dollar buc converter.