Ron Petterson
Member
A couple weeks ago I posted a question for an 8N with front mount distributor and the following was provided by Bruce.
I am getting back to checking each step and have a question or two.
First for clarification, I am using an Ohm Meter that does not have a adjustment. when the two leads are touched, the meter read .2 ohms
My comments after each of the steps I have completed.
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.
Comment" Points open 6.3volts, Points Closed 3.7 Volts
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.
Comment: The breaker plate is new. The insulator is new and the points (Blue Streak) and condenser are new)
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.
Comment: Before I replaced the coil onto the distributor, I checked the resistance between the coil wire lead and the pigtail and it read a quick 1 ohm, dropping to .8 within a second or so. Does this give the
same reading as if the coil was attached to the distributor and if so, how would one read that when it is almost impossible to get to the inside of the distributor
when attached to the engine? Would the .2 need to be adjusted for the coil reading and if so, does ,6 indicate a failing coil?
3. The copper strip is broken or grounded to the plate. (look very carefully for cracks & breaks) .
Comment: Again all new parts, nothing broken.
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.
Comment: From everything I can determine, ground is good. Points plate new, no oil.
The following have not been completed yet. Couple of questions.
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.
Question: What is the easiest way to measure this. One lead at the top of the coil, where is the other ohm meter lead attached?
Question: Is there anything I have listed that indicates any problem so far? If not, I will proceed further with those that would be not be a result of wear due to
replacement of parts or moisture since I did check that within the distributor.
Thanks
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. 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.
* 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.
I am getting back to checking each step and have a question or two.
First for clarification, I am using an Ohm Meter that does not have a adjustment. when the two leads are touched, the meter read .2 ohms
My comments after each of the steps I have completed.
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.
Comment" Points open 6.3volts, Points Closed 3.7 Volts
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.
Comment: The breaker plate is new. The insulator is new and the points (Blue Streak) and condenser are new)
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.
Comment: Before I replaced the coil onto the distributor, I checked the resistance between the coil wire lead and the pigtail and it read a quick 1 ohm, dropping to .8 within a second or so. Does this give the
same reading as if the coil was attached to the distributor and if so, how would one read that when it is almost impossible to get to the inside of the distributor
when attached to the engine? Would the .2 need to be adjusted for the coil reading and if so, does ,6 indicate a failing coil?
3. The copper strip is broken or grounded to the plate. (look very carefully for cracks & breaks) .
Comment: Again all new parts, nothing broken.
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.
Comment: From everything I can determine, ground is good. Points plate new, no oil.
The following have not been completed yet. Couple of questions.
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.
Question: What is the easiest way to measure this. One lead at the top of the coil, where is the other ohm meter lead attached?
Question: Is there anything I have listed that indicates any problem so far? If not, I will proceed further with those that would be not be a result of wear due to
replacement of parts or moisture since I did check that within the distributor.
Thanks
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. 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.
* 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.
