What coil?

tracto-man · Nov 5, 2016

I've never been good at electrical stuff. Would like to try a different coil on this gas massey Harris(?) 50. Have a couple 12 volt round style coils around, but would they work? Are the round style 12v coils kinda universal or is there special ohm resistances or that kinda thing that's different? Could I just try a 12v coil from tsc?

Thanks in advance.

rockepg · Nov 6, 2016

They are pretty much universal. As long as your electrical system is 12v then give it a try.

old · Nov 6, 2016

There are 2 or more types of coils. Some are 12 volt needing an external resister and some are 12 volt no external resister needed. Most unless wore off will say right on them 12 volt no external resister needed or 12 volt external resister needed. As far as telling them apart it can be done with an ohm meter and the one needed an external resister will have a lower reading then the one not needing one but I can not tell you what each would read off the top of my head

rockepg · Nov 7, 2016

I agree old that there has been several varieties over the years. Some with and without resisters, some larger diameters than others etc. While i completely agree in the long run it should be wired according to the specific type he will use, it'll be just fine to use what he has for testing. Since he has the resister already there even a unit with no resister required will fire just fine. A little less output is all that will happen.
Assuming of course this is a sub question to tracto-man's other post on trying to troubleshoot that starting issue.

rvirgil_KS · Nov 7, 2016

"Since he has the resister already there even a unit with no resister required will fire just fine. A little less output is all that will happen."

From my experience I disagree. If it will run at all I would expect hard starting. If it does start, a likely symptom will be that the starter will crank and crank and engine will only start when start button is released.

If coil requires no added resistor, to use one would only add to frustration in trying to diagnose problems.

old · Nov 7, 2016

NO coils have built in resister they are just wound different so as to increase the ohm so as to work on 12 volts with out a resister. A coil made to work on 12 volt no resister will work some time with a resister but I sure would not do it that way due to weaken spark. When I got one of my Case VAC tractor it had a coil on it that said no external resister needed but the guy had it wired with a resister which I took off. Tractor runs and start very well

tracto-man · Nov 7, 2016

Thanks for the replys. I'll just try a 12v round coil. Says no external resistor required so for now I'll just bypass the resistor and see if it fires.

rockepg · Nov 7, 2016

Agreed it would be best to take the time and read the label. In a pinch he can plug in what he has and try it. Pull a plug and put it back in the wire, lean it against the block or valve cover or somewhere he can see it while cranking. If it has spark or not should be clearly visible. Yellow spark would fall inline with what rvirgil_ks was saying about to weak while blue spark is "normal". Charge up that battery too tracto-man. Looks like you are at about 75% with your meter reading.

tracto-man · Nov 7, 2016

Picked up a coil with no resistor needed at TSC for less then $30. Popped in on and checked voltage, checked points again, put it all back together, and checked for spark with a plug. Nothing. Grabbed the spark tester, showed spark. Put the plugs in, turned it over, bit a choke, fired right up. Coughed black smoke for a couple minutes and then acted like an extra cylinder had just turned on and ran great. Will change the fluids and go from there. Thanks for your help!

What coil?

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