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8n no spark

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Author  [Modern View]

05-14-2018 12:50:58

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If you get six volts across thr resistor going to the coil you can eliminate that as a problem yes? There’s no other test necessary to eliminate thr resistor as a problem of no spark at all.?

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Tim PloughNman Daley

05-15-2018 03:39:12

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 Re: 8n no spark in reply to robert1234, 05-14-2018 12:50:58  
You have an early 8N with the front mount distributor we've established. Is the battery 6-volt or 12-volt? This is important. Just because you have a 6-volt battery does not mean the system is wired correctly. If 6-volts, is it wired positive ground as it was originally? That means you also have a generator and a voltage regulator. Get a copy of WIRING PICTOGRAMS by JMOR and find your set up. Then take your battery in to a starter shop to be tested. While he does that go thru your wiring per the diagram. Do not go by wire colors as harness may not be original. Do continuity tests to verify every wire is connected correctly. I highly suspect your resistor is not the root cause of your problem. Bad/wrong wiring is usually the culprit so start there. Get coil tested -6V or 12V? Next would be the distributor...when was the last time you did a tune-up? How did you check for spark?

Tim *PloughNman* Daley(MI)

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05-15-2018 16:40:52

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 Re: 8n no spark in reply to Tim PloughNman Daley, 05-15-2018 03:39:12  
Luckily I kept checking wiring turned out to be bad ignition switch, the guys on this board are always helpful

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05-14-2018 16:07:59

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 Re: 8n no spark in reply to robert1234, 05-14-2018 12:50:58  
i should have mentioned that when i discovered the coil was not the source of my ignition issue, i put the 6 volt coil back in. i'm really curious to see how long it will last. when it finally does fail, i have two twelve volt coils on hand to replace it with, due to a shipping mixup :)

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05-14-2018 16:04:24

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 Re: 8n no spark in reply to robert1234, 05-14-2018 12:50:58  
define "any length of time." i removed that resistor from my 12 volt system with its six volt coil. last summer, i thought i had finally fried the coil after six years. but i was wrong, the twelve volt coil i got did the same thing. turned out the problem was either my ignition switch or condensor. i'm now into my seventh year of ~ 25 hours/year of running without that resistor.

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05-14-2018 13:19:58

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 Re: 8n no spark in reply to robert1234, 05-14-2018 12:50:58  
no. if u want to eliminate the resistor as a problem, jumper around it. if that doesn't fix your problem, then u can (probably) eliminate it as the cause.

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Bruce (VA)

05-14-2018 13:20:12

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 Re: 8n no spark in reply to robert1234, 05-14-2018 12:50:58  
Front or side distributor? OEM ballast resistor or the infamous white ceramic blob?

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05-14-2018 14:51:24

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 Re: 8n no spark in reply to Bruce (VA), 05-14-2018 13:20:12  
Front distrutor, resister looks like the original not real white and not veery wise, if I jump around it and it starts I iassume I’ll damage something if I run it for any length of time. Yes

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Bruce (VA)

05-14-2018 16:27:35

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 Re: 8n no spark in reply to robert1234, 05-14-2018 14:51:24  
If it is the oem ballast resistor, jumping it to see if the tractor will run will not hurt your 6v coil......as HFJ said.

But, if you have 6 volts on the coil side of the resistor, it's unlikely that you have a resistor problem.

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, 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.

** Yesterday's Tractor kit:

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

** Distributor cam lube NAPA:


*** 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

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