Help - 1951 8N Not Catching

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Posted by Keelan on June 14, 2021 at 09:13:06 [URL] [DELETE] :

Hello!

I was tasked this spring with getting the 1951 8N my grandfather purchased back in '56 up and running. Its been temperamental to start for at least a decade, and this spring it appears to have given up.

A little background:

We use this tractor mostly for brush hogging, hauling logs, and pulling around a small trailer for property maintenance during the summer months. Its kept in a shed all year, so in general is in fairly good condition.

My father has been looking after the tractor since my grandfather passed away, and while he's fairly handy, he's not overly mechanically inclined and his maintenance has mostly extended to greasing the fittings, changing the oil, and replacing the odd part (spark plugs/distributor cap, etc).

My background is in mechanical engineering, but my professional career veered off into the commercial lighting industry, so while I'm well grounded in electrical/mechanical principals, my knowledge on engines and specifically those from the 1950's is lacking.

So here's what I can tell you:

The tractor is still a 6V positive ground system, and over the years it takes a lot of cranking by the starter motor to get the engine to catch. Especially when its cold out (10-15C), its pretty easy to kill the battery without the engine ever firing up. Recently it also seems that the spark plugs foul with carbon deposits fairly quickly.

This spring when getting it up and running, I finally managed to get the engine to catch, but it was struggling to develop power. I let it run for a while, and then managed to drive it around a bit to see if I could work something through its system, however it eventually sputtered out and died. I was unable to get it running again.

So here's what I've done to date:

Checked the carburetor and air filter to see if there was anything interfering with supply to the engine (possibly too rich resulting in the carbon fouling). Nothing seems amiss, and fuel is getting into the carburetor from the tank (flow does not seem impeded). I also purchased a new battery and spark plugs.

Still was unable to get it to start.

I had a mechanic come to take a look at it over the weekend (older fellow, been working on tractors for at least 5 decades), and here's the result of about 3 hours:

Getting a spark
Checked the timing (looks accurate)
Getting compression
Replaced the spark plug wires
Replaced the points

We eventually pulled out the ignition coil, and it was listed as a 6/12V unit (for 12V use w/ external resistor). This didn't sit right with my mechanic, so he suggested we replace it. In speaking with my parts supplier, it seems like this is fairly common these days, and while I'll replace it anyways, it doesn't sound like this is the likely source of the problem.

So here's where I need some guidance. I'm not sure what other diagnostics I should perform, and neither my mechanic nor I can seem to figure out what the fault is that is causing the engine to not catch. I'm up to work on it again in a few weeks, so any/all suggestions of things to check would be welcome.

Thanks in advance!


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