8n - no spark

Firstly, I've searched and haven't found the exact same problem, at least how far I've dug into it. I have a 50 8n, side mount distributor, 6v, foot push starter. I haven't had it running yet and don't have spark at all. I replaced the fuel system and wiring harness since everything was clogged and rusted, as well as the plugs, points, condenser, and distributor cap, and plug wires. It had been sitting for I don't even know how many years. It turns over no problem, but there's no spark after replacing those things. Couldn't get a spark or reading from the main plug wire that goes to the dist from the coil, although trouble light lit up at the + and - posts on the coil. That being the case, I got a new 6v coil and still the same thing. I made sure the point is set to .025, as well as the plugs, plugs are hooked up correctly to the distributor, 1,2,4,3, tip of the button is on 1, then the order counter clockwise. Am I missing something from just that explanation? Again, I apologize if I missed an obvious post that has this.

Your ignition system has 2 separate circuits, primary and secondary. The primary circuit goes from the battery to the ignition switch to the negative side of the coil out on the other side of the coil to stud on the side of the distributor then to the points.

The secondary circuit goes from the coil through what you are calling " the main plug wire that goes to the dist from the coil". The voltage flows from there to the rotor, cap, wires then plugs.

The only time you have voltage on the secondary circuit is when the points open which causes the magnetic field in the coil to collapse.

It's easier and simpler to follow the primary circuit; that's where most problems usually are.

First, get a multimeter. Your light only tells you that you have voltage. It could be 3 volts, less thn half of what you need to make it work.

Next, charge the battery. The number one cause of a weak spark is a weak battery. You need 6.35 volts.

Confirm that you have voltage to the coil. Battery voltage, points open. About half that if the points are closed.


Do you have battery voltage across the points when they are open? (with the points open, put one probe on one side of the points & the other probe on the opposite side of the points) Verify the gap on the points at .025. Then, 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. (I always spray my feeler gauge blade off w/ contact cleaner.) Make sure you have voltage across the points, as in past the insulator on the side of the distributor. That is a very common failure point on sidemounts, along w/ the attached copper strip. It's hard to find a short there because it is usually an intermittent . So 'wiggle' the insulator & the copper strip a bit when you are doing your checking. If you find the short there, the Master Parts catalog lists everything you need on page 154. You can make the strip and you could also make the insulators as well. But, somethings are just easier & in the long run cheaper to buy. Get the strip, 12209, screw 350032-S, 12233 bushing & 12234 insulator & just replace it all.


If you just replaced the rotor & lost spark, put the old one back in. Insure that the rotor fits firmly on the shaft & that the little clip is there. Make sure the distributor cap is not cracked, doesn?t have gouges in it from the rotor or brass shavings & doesn't have carbon tracks. Check continuity on the secondary coil wire. Make sure it is firmly seated in both the cap & the coil. Next, remove the secondary coil wire from the center of the distributor cap, turn the key on & crank the engine while holding the end of the wire 1/4" from a rust & paint free spot on the engine. You should see & hear a nice blue/white spark. If not, you have a bad coil or condenser. Just put the old condenser back in to eliminate that as a possibility.


Post back w/ results; I'll be interested in what the problem was.
75 Tips

Clean the new points, then clean again!

Sorry to barge in on this thread but I have a no spark issue also and hoping Bruce can make some sense out of my problem for me. 51 8n, 6v side mount, new plugs, points, condenser, rotor, cap went to napa and bought good ones. Been reading tons of archives and did all the basic testing, checked the copper strip, the insulator, cleaned feeler gauges every time I use them, cleaned the new points and then cleaned again, used the dollar bill trick to clean also anyway did all the basics and still no spark. Did testing on the switch, that's good then went on from there. Testing from batt. to coil, 6+ volts, coming out secondary wire to dist. 6+ volts if its not connected to dist. When connected to the dist. the secondary wire reads 0 volts. No power to dist. When connected to dist. I have 5 volts on the batt. side a nd 0 volts to the secondary side. No voltage to dist. at all. I know coils don't go bad often but is maybe there a short in my coil??? Any help would be much appreciated. Thanks guys

' I know coils don't go bad often but is maybe there a short in my coil???"

Probably not.

You will never see voltage on the secondary circuit unless it's running. Then, at 22kv or so, it will fry your meter.


Your points are grounded.

Do you have battery voltage across the points when they are open? (with the points open, put one probe on one side of the points & the other probe on the opposite side of the points)
75 Tips

Bruce, nope, no volts on the points...

Bruce, I may have used the wrong terminology speaking of the secondary wire, I found a wiring diagram and it calls it the primary wire. It is not the high tension wire (secondary) that goes from the middle of the coil to the middle of the dist. cap, it is the low tension wire (primary) that goes on the stud on the dist. Hope you can read minds and figured out I don't really know what I'm talking about. Sorry....

Test the wire for continuity w/ your meter.

If it has no continuity, yo found the problem.

If the wire is good, hook it back up to the distributor and turn the key on. Open the points and start looking for battery voltage. As I said above, make sure you have voltage across the points, as in past the insulator on the side of the distributor. That is a very common failure point on sidemounts, along w/ the attached copper strip. It's hard to find a short there because it is usually an intermittent . So 'wiggle' the insulator & the copper strip a bit when you are doing your checking.
75 Tips

Continuity good on the primary wire. 6+ volts when not connected to dist. on both sides of coil. After I connect the primary wire to dist. 5 volts on the other side of the coil, 0 volts on primary wire. Is this ok??? No volts on points, the copper strip is home made with a wire and a connecter on each end. I pulled the insulator out looks good and reinstalled. Tractor was running in spring of this year.

with the points open you should show battery voltage, If they are open and you do not show battery voltage, you have short to ground.

" No volts on points, the copper strip is home made with a wire and a connecter on each end. I pulled the insulator out looks good and reinstalled. "

It does not matter how it looks or how long it conducted voltage. If it was still good, you would have battery voltage across the open points.



As I also said above...?? the Master Parts catalog lists everything you need on page 154. You can make the strip and you could also make the insulators as well. But, somethings are just easier & in the long run cheaper to buy. Get the strip, 12209, screw 350032-S, 12233 bushing & 12234 insulator & just replace it all.
75 Tips

Ok got it, will get the new parts and go from there. Thanks Bruce, for all your help.....

Thanks for your response, I'll use my multi-meter in a bit. The batter is new and fully charged, but I'll double check the voltage to the coil and then check the points. I'll respond back once I've had a chance to check it out.

I've got 6.32V at the coil, and on both sides of the points, open and closed, which is weird, no voltage at the post on the side of the distributor or the + post on the coil though, open or closed, so I'm guessing there's a short on the copper strip, if I'm following this right, and it's entirely possible I'm not lol.

scratch that last reply, I've got 6.32 volts across the points when open. Going to clean them in the morning and then see I think.