Trouble bench testing points and coil 8N Front mount

HeyObie

Member
My 8N Front mount stopped running. It was getting rougher and rougher and eventually gave up. No spark

So I ordered new points (blue streak gap.013), cap, rotor, condensor and 6 volt coil. new wiring harness. Still no spark. I had 6volt going to the coil.

Frustrated with the number of times I have pulled and installed that I need to bench test.

So I pulled the battery and bought a new resistor so I could figure this out on the dining room table.

So here is my bench setup. Connect -neg of 6V battery to resistor, resistor to top of coil,I have the rotor pointing at one of the spark plug holes in the dist cap and I know the points are closed. I take my meter, set the meter to ohms. I attach one probe to the +pos battery terminal and the other probe to the spark plug hole.

I am expecting the spark to jump across the rotor to the distributor cap and complete the circuit. I get nothing.

I know the pigtail is good, the coil to the distributor cap is good and points are working. It must be a bad coil but I want to know if my above testing procedure is correct. Will the spark jump between the rotor and the distributor and complete a circuit?

Thanks,

Obie
 
Your circuit description reads like you need to reread basic circuits... You never use the OHM range to try to complete a circuit...

There are two circuits involved... Primary and Secondary...

RE-READ!
 
No, your testing procedure is not correct.
You measure ohms with power disconnected. No battery.

You can test the continuity of the points and coil with ohms,
but it isn't going to measure anything to the plug wires.
Unless your rotor actually touches the cap, which it shouldn't.

You can also use a voltage testing bench setup, which is different.
Then you would need to measure voltage, not ohms.

Search for the testing procedure Bruce (VA) has posted many times.
Just in case it wasn't a typo, point gap is .015.
Let us know what you find! :)
 

I'm sorry for my error. I am trying to see if I am getting spark using my bench test.

So if I switch to Volts on the meter and put the meter between the spark plug wire hole (rotor pointing at the testing spark plug hole) on the distributor cap and the positive battery terminal to complete the circuit, then I should pick up voltage.

Is this correct?
 


The first thing you need to check is for battery voltage at the coil. Yes, you need a meter for that, not a light. With the key on, you should see battery voltage battery with the points open and about half that with the points closed. If you do not see either, the problem is between the battery and the coil, e.g., the resistor, ignition switch or a bad connection.

Assuming that the bushings & advance weights are ok (*see below), & that you have correct voltage to the coil , the most common reasons for no spark or a weak spark on the front distributor are below. Check each one carefully. Even if you find a problem, check all 10:

1. The insulator under the brass concave head screw & where the copper strip attaches. (it's fiber & will wear out; poke & prod w/ your meter leads to make sure it still works) If you need to replace the insulator, use a .250 x 3/8 nylon square nylon anchor nut available at most big box home stores.

2. The pigtail at the bottom of the coil not making contact w/ the concave head brass screw inside the distributor. (With the coil on, the pigtail must firmly contact the brass screw. No contact = no spark) Check for continuity between the top of the coil and the pig tail; a 6 volt coil will be around 1 ohm & a 12 volt coil should be 2 to 3 ohms.

3. The copper strip is broken or grounded to the plate. (look very carefully for cracks & breaks) .

4. The distributor is not grounded to the block because of paint or grease acting as an insulator. Or the points plate is covered in oil.

5. The tab on the bottom of the coil not making contact w/ the brass button on the cap. (With the cap on, the tab must firmly contact the brass button. No contact = no spark.) Check for continuity between the top of the coil and the tab; you should see about 6k ohms.

6. A grounding issue inside the distributor: Incorrect positioning of the spring clip on the plate causing the pigtail to ground. (the open part of the clip goes between 7 & 9 o'clock on the plate. That puts the straight part of the clip opposite of the timing screw at 3 o'clock) or the condenser wire is grounding to the plate or side of the distributor.

7. Incorrect seating of the coil on the distributor due to a loose bail or no gasket.(the coil must not move at all; if it does, replace the gasket or bail. Or stick some cardboard under the bail).

8. Water/moisture inside the cap due to gasket failure or the absence of a gasket. (the cap AND coil have gaskets)

9. Dirty/corroded/burned/incorrectly gapped or misaligned points. I use only Wells, Blue Streak or Echlin brand points (* *see below). If you are using quality points and cannot get the gap to open to .015, (NOT .13) chances are you need to replace the bushings. If the shaft has any sideways movement AT ALL, the bushings must be replaced. (*** see below) If the tractor has been sitting unused for a few months, it?s highly likely that the points are glazed. Dress them with brown paper or card stock. Do NOT use a file or sandpaper. That removes the thin metallic coating on the surface and reduces point life considerably. With the points closed, you should have continuity between them; high resistance means they are glazed.

10. Burned rotor, cracked/carbon tracked cap. Brass ?dust? in the cap is a sure sign of bushing wear.

After find the problem & re-check the point gap, do a continuity check before you put the distributor back on the tractor. Before you start, make sure your meter/light works.

With the distributor still off the tractor, 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. Put the coil on the distributor, 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 misaligned trying to put it back together, one piece at a time. The result is something gets broken or you get a 'no spark' problem.

It's possible to put it back on wrong & break it. Look at the slot on the end of the cam shaft. Whatever 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). 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. Hand tighten the two bolts until the distributor body is flush with the timing gear cover.

* Unscrew the plate hold down screw & remove the C clip to get the plate out. Remove the shaft & weights. The weights should freely move. The tracks should not be wallowed out.

** NAPA part numbers:

. Points: FD-6769X or ECH CS35

. Condenser: FD-71 or ECH FA200

. Rotor: FD-104 or ECH FA 300

. Cap: FD-126 or ECH FA 350

** Yesterday's Tractor kit:

Premium Blue Streak points (A0NN12107ABS), rotor, condenser, and gauge Part
No: APN12000ABSR

** nnalert's kit:

Heavy-Duty Point Set, Condenser, Heavy-Duty Rotor, Heat Range Matched Spark Plugs. Packed 6 to Master Carton. Contains: 1-9N12107 Point Set, 1-AONN12300A Condenser, 1-9N12200 Rotor,1-9N12104 Gasket Kit,4-AL437 Spark
Plug,1-015 Gauge, 1-025 Gauge.

** Distributor cam lube, Mac's Auto Parts:

http://www.macsautoparts.com/.../distributor-cam-lube...
one-7-8-ounce-381629.html?utm_source=google&utm_medium=paid_search&utm_campa
ign=paid_search_google_pla&scid=scplp58-20966-1&sc_intid=58-20966-1&gclid=CN
7P-sjQ9tICFYePswodaH0HRg

** Distributor cam lube NAPA:

https://www.napaonline.com/en/p/ECHML1

*** There are three ways to replace the bushings in a front distributor:

1. Buy new bushings (part numbers 9N12120 front & 18-12132 rear). Press out the old ones, press in the new ones and ream to fit. CAUTION: do not try this unless you have a press & know how to use it. If you break the base, a new one costs $130. If you bend the tower which holds the front bushing, a new plate will cost you $30. Resist the temptation to buy a new plate; most are pot metal and the threads will wallow out about the third time you change the points.

2. Take the new bushings and distributor to your local machine shop.

3. Send the distributor out for bushing replacement if you do not have a local machine shop
75 Tips
 
Don't worry about any errors. We all help each other get past them.
I would forget about measuring the spark plug hole all together.
Unless you have a high voltage probe and special equipment.
I see Bruce responded to your post. I recommend following those steps.
 
hey Obie........you do know yer rotor inside yer capple is NOT supposed to touch, don't you??? Yer sparkies JUMP the gap (0.005) inside yer capple, just like inside (0.025) yer cylinder. 95% or all ignition problems are the POINTS. (0.015) Even brandie NEW points have the same problem. INVISIBLE CORROSION between the points. Me? I stick the corner of $1-bill (cheap) between the points and PULL. Polish the invisible corrosion off'n the points. Iff'n yer really cheap, the cardboard of paper matches will also due itt. Oh yeah, coils and condensers seldom go bad but points (0.015) due. One final thing, keep yer itchy-twitchy fingers off'n them handy-dandy carb tweek-ums. They seldom go bad. Howsomevers....iff'n ya did, fess-up and I'll tell you the EAZY way to adjust yer carbie.......Dell, yer self-appointed sparkie-meister
 
Thank you guys for the guidance. Bruce I followed your tests. Everything looks good. The distributor is new, blue streak points installed, new condenser, new rotor and new cap and new coil and gapped to .015. Electrically, everything checks out.

The only thing I can not verify is whether the distributor cap is touching the contact from the coil. That is what I was trying to accomplish with my failed bench test.

Anyway, tomorrow, ill put it back on. when I had it connected on the 8N, I was getting 6 volts to the coil. But tonight, I tested the OEM resistor and it is wacked. Could not get any resistance. Then anywhere from 5 thru 50. Took it off and will replace it with a new one I bought
 

Thanks Dell. I realize the rotor doesn't touch the cap. But I figured if I connected it to a freestanding battery, it would jump the gap. But the test is more complicated than that. I guess you need to ground the distributor. Anyway, I am just going to put it back on and see what happens
 
To bench test a front mount. I place it in my vise. Use my battery charger and hook the negative to the coil and the positive to the distributor base. Use a spark plug wire and my spark tester. Turn on the battery charger and then turn the drive by hand and watch the tester for a spark.
 
(quoted from post at 10:46:59 11/20/17) To bench test a front mount. I place it in my vise. Use my battery charger and hook the negative to the coil and the positive to the distributor base. Use a spark plug wire and my spark tester. Turn on the battery charger and then turn the drive by hand and watch the tester for a spark.
.......and turn it in same direction as when on engine.........no spark to plugs in rotated in wrong direction.
 
Check where the spring touches the concave screw and the flat conductor are connected that connect to the points. There is a fabric insulator that isolates the screw from the distributor base. This insulator can get shorted out and cause a no spark condition.
Zane
 
Well I finally got it going. Thank you all for taking the time to educate me. I learned more than I wanted to but it was what I needed to get it running.

Obie
 
Glad to hear you got it going again Obie.
Did you find the root cause or did it just work
when you put it back together and on the tractor?
 
(quoted from post at 20:07:48 11/21/17)
I believe the problem was a bad coil and bad connections between coil and distributor and cap.
ither would stop it working. Don't need two causes. i.e., don't know what the problem was.
 
Bruce, I'm brand new to the forum. That was quite an informative post on Obie's issue. I need to figure out how to bookmark that for future use. Thanks.
 
(quoted from post at 15:11:22 11/22/17) Bruce, I'm brand new to the forum. That was quite an informative post on Obie's issue. I need to figure out how to ebookmark that for future use. Thanks

I agree. Awesome troubleshooting guide I did a copy and paste and put it in a Word document and where I keep all kinds of stuff about these a Tens
 

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