Re: Coil or condenser

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Posted by Tim Daley(MI) on November 13, 2017 at 07:34:11 [URL] [DELETE] :

In Reply to: Coil or condenser posted by BeanStalk on November 12, 2017 at 18:20:25:

I don't know what O'Reilly's coils are like quality-wise, I don't buy much there especially parts for my tractors, maybe oil, but that's it. I and many others here use the more reliable places for Ford tractor parts. Do you have the old coil? Have you tried that? Your statement below is ambiguous -you say you measured resistance and get 7.14 Ω - to + post 1.5 Ω. What is Plus to Minus? The round coil for angle-mount distributors has two stud terminals. One is the Battery connection, the other is the Distributor connection. Just charging the battery doesn't mean it is good. How old is it? Low-budget batteries have a lifespan of 2 years at most usually. Check specific gravity of each cell with a hydrometer. The battery must sustain a charge under load. You can also take the battery to your trusty local starter/alternator rebuild shop and they will bench test it with the proper equipment. Some franchise auto parts stores say they test batteries too, but I'd trust a starter shop over anyone else. From Bruce(VA):

You need a strong battery to:
1. Close the solenoid
2. Spin the starter
3. Engage the Bendix
4. Provide voltage to the coil.

As the battery gets weaker, the first thing to fail is your spark. If the battery is almost totally dead, all you will hear is the solenoid clicking.

The more current you use to spin the starter, the less you have for the ignition.

Coil problems are difficult to diagnose. For starters, round coils are pretty robust & square coils arenít (because of the difference in insulation used), but neither one will hold up to a poorly done 12v conversion that allows too much current to the coil or leaving the key on (see tip # 38). Too much current creates heat which melts the insulation. Insufficient resistance in a 12v conversion will do the same thing. Rarely do coils just ďgo bad.Ē
There are a few ways to see if a coil is bad, but itís not possible to determine if a coil is good w/o some expensive testing equipment. If you detect a dead short or high resistance in the coil w/ an ohm meter, itís bad. If itís cracked, itís bad. If a sidemount coil w/ battery voltage to the primary will not jump a ľĒ gap from the secondary wire to the block, itís bad. But, here is the hard part: even if you do not detect a short, even if it will produce a spark, even if itís not cracked, that doesnít mean the coil will work when itís hot & under a load. So, itís a process of elimination. If the tractor starts & runs fine for 30 minutes or an hour then cuts off & refuses to re-start, and you checked for spark at the plugs & it had no spark at all, AND you have the correct voltage at the coil thatís a good sign that you have a bad coil. Let it cool off, restart it & if you have a good spark, odds are itís a bad coil. But, even then, you might end up w/ a spare coil on the shelf!

Bottom line.......coils do go bad, but I'll venture a guess that 75% of new N coils sold today are sold to folks who do not understand how to diagnose a poor spark problem or how a coil works. So, for those who donít know any better, in a no spark situation the first suspect is usually the coilÖÖand, more often than not, it isnít the problem.

Before you check anything else, make sure you have the correct voltage at the top of the coil. It should be battery voltage w/ the points open & about half that w/ the points closed.

If you do not have the correct voltage at the coil, thatís your problem. And, it sounds like that is the first place to look because you should have battery voltage w/ the points open.......do you?

Assuming that the bushings & advance weights are ok, & that you have correct voltage to the coil, the most common electrical failure (no spark, weak spark) points on the frontmount are:

1. The insulator under the brass concave head screw.
2. The insulator at the end of the points where the copper strip attaches.
3. The copper strip is broken or grounded to the plate.
4. The condenser wire grounding.
5. The pigtail/tab not making contact.
6. Incorrect positioning of the spring clip on the plate causing the pigtail to ground.
7. Incorrect seating of the coil on the distributor due to a loose bail or no gasket; the coil must not move at all.
8. Water/moisture inside the cap due to gasket failure or the absence of a gasket. (that probably caused the problem; dry the cap & distributor w/ a hair dryer & replace all the gaskets)
9. Dirty/corroded/incorrectly gapped points
10. Burned rotor, cracked/carbon tracked cap.

Unless the coil is cracked or shows a dead short, chances are it's fine; square coils rarely fail cold. Pull the distributor & do a continuity check.

First, make sure your meter/light works (don't ask....)
Next, dress the points by running a piece of card stock or brown paper bag through them. New points sometimes have an anti-corrosive dielectric coating on them & old points can corrode or pick up grease from a dirty feeler gauge or excessive cam lubricant. Then, check the gap at .015 on all 4 lobes.
Now, follow these steps:
1. Coil off, cap off, points open. One probe on the brass screw & the other on both sides of the open points. On the side closest to the cam, you should have continuity. Not on the other side! If you do, you will also have continuity everywhere because the points are grounded.
2. Coil off, cap off, points open. One probe on the brass screw & the other anywhere on the body of the distributor. You should have no continuity! Now, rotate the tang on the distributor....as the points open & close, you have continuity (closed) and lose it when they open.
3. Coil on, cap off, points open. One probe on the lead on the top of the coil, the other on the cam side of the open points. You should have continuity!
4. Coil on, cap off, points open. One probe on the lead on the top of the coil, the other anywhere on the body of the distributor. You should have no continuity!
At this point, I just put the distributor, coil & cap all back on the tractor as a unit. The reason I do this is because it is real easy to get the cap or coil mis-aligned trying to put it back together one piece at a time & the result is something gets broken or you get a Ďno sparkí problem.
It's possible to put it back on wrong & break it. Look at the slot on the end of the cam shaft. What ever angle it happens to be, turn the distributor tang to match it. Make sure you can tell the wide side from the narrow side on both the cam & distributor! (close counts) Then place the distributor on the front of the engine, gently push it in place & slowly turn the distributor body until you feel the tang slip into the slot. Rotate the distributor body until the bolt holes line up. Then, hand tighten the two bolts until the distributor body is flush w/ the timing gear cover.
Finally, double check your firing order & plug wires. Itís 1-2-4-3, counterclockwise. Itís very easy to cross 3 & 4.
Post back w/ results & any other questions.

Iíll add :

Double check ALL the wiring as well. Get a copy of Wiring Pictograms by JMOR from our HOW-TOís forum and use it as reference guide. Trace every wire; do not just go by the Ďcolor-codingí on the wires. Perform a true continuity test with your Multi-Meter. Start by taking the light circuit out of the equation Ėoften times fellas have shorts in their cobbled up lighting wires. Disconnecting the lights, temporarily, will help in diagnosing any electrical issue. Do you have the correct ballast resistor? Once you determine the battery and wiring are all good, Iíd start looking into the distributor itself.

Tim Daley(MI)


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