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no spark

R

reomack

Member
48 mutt with 51 engine, 12v 1 wire conversion, good compression, good fuel flow, good primary ignition circuit, 12.6v on hot side of coil with points open and 0v on distributor side, 12.6v on both sides of the coil with the points closed. No spark when coil wire is pulled from the distributor and held approximately 1/8-1/4 inch from ground. I have not checked the coil resistances yet but that is most likely my next step. can anyone tell me what they should be or maybe give me some guidance if what I have done so far is wrong.
 
(quoted from post at 11:32:12 11/18/18) 48 mutt with 51 engine, 12v 1 wire conversion, good compression, good fuel flow, good primary ignition circuit, 12.6v on hot side of coil with points open and 0v on distributor side, 12.6v on both sides of the coil with the points closed. No spark when coil wire is pulled from the distributor and held approximately 1/8-1/4 inch from ground. I have not checked the coil resistances yet but that is most likely my next step. can anyone tell me what they should be or maybe give me some guidance if what I have done so far is wrong.
Click to expand...
just checked the secondary of the coil and on the 200K ohm scale, it shows infinite resistance, so the secondary isn't grounded. Ideas?
 
NOT sure exactly what you are asking, but the coil secondary is NOT supposed to be grounded, the primary and secondary are in series, more or less an "autotransformer". Are you measuring from the coil's case to the secondary terminal, or from the primary terminals?

Measure from the high-tension terminal to both primary terminals, would expect to see 10K (?) to either, with a slight variance between them to account for the (low) primary resistance of the coil.
 
Measuring from the secondary to ground. I know it isn't supposed to be grounded, just wanted all to know that I had checked it and that it was OK. I don't know what else to check. I guess the only thing left is the coil wire.
 
"Measuring from the secondary to ground."

So go ahead and measure from the high-tension terminal to both primary terminals, and see what the secondary resistance is.
 
pull the no 4 plug out. lay in on the side if the engine where it is touching and spin the motor and see if you have spark. that's the best way to know if you have fire at your plugs. don't hold the wire unless you use pliers with rubber handles. plug has to be touching metal for a ground. wouldn't surprise me if you do have spark.
 
"12.6v on hot side of coil with points open and 0v on distributor
side, 12.6v on both sides of the coil with the points closed"

This sounds backwards to me. Are you sure this is right?
 
Reomack, I agree with royce. Do this, remove the wire from the coil to the distributor. Hook up your ohm meter from a good clean ground to that wire, so you are looking into the distributor. Then open and close the points. You should see zero ohms with the points closed and infinity with them open. Anything else, you have something wrong with the points, the wire going through the grommet or maybe a shorted condenser. If this test passes, then I would suspect the coil.
 
OK, I pulled the coil and checked it for resistance. primary to secondary is good, primary to ground is inf. when every thing is put back together I now have a very weak spark from plug wire to ground, not hot enough to fire the engine. I'm pulling my hair out and I don't have that much left to pull.
 
I think I may have found the issue. Pulled the points off and measured the resistance across them and it was 26 ohms. Should be zero. Should have checked that early on. I hate it when I do dumb stuff.
 
It's running!! Put new points and plugs in, cranked the engine with the distributor cap off to look for normal sparking at the points and saw it. Put the cap back on, turned on the gas hit the starter and bingo. Running like a top. Lets see, I hauled it 85 miles to my home, removed the fuel tank/hood assembly, dumped about two gallons of bad gas and replaced the fuel shutoff/sight glass. Pulled the head and cleaned it and the block up, repaired two stripped threads in the block. reassembled everything, put in a new battery, messed with it for two weeks, then replaced the points and plugs. After running it for about 20 minutes I retorqued the head. It took about 1/8 turn on the bolts to get to 70 ftlbs. I'm pretty happy with my 71 (early 48) year old 8N. Drove it around my neighborhood and got some very stange looks. I deserved them though as right now I look like a dirty old bum, but a happy one.
 
Good news. Thanks for the up-date. So many times, it's the simple thing that needs fixing. I think it's Bob G. that says, look for the simple and cheapest thing first.
 
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