A few years ago, my neighbor mentioned to me that he had diagnosed a no spark condition on his 8N and fixed it by replacing the coil. I asked him if I could
have the old coil. I put it on one of my tractors were it remains today.?
I don't know why his tractor had no spark. I don't know why it ran after he replaced the coil. But I do know the coil on the tractor wasn't defective.?
Your coil was cracked, so we can assume it is defective. And, for the moment, lets assume the new coil is good.
Assuming further 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:
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
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