How do I test the distributor?

Howdy Folks! I went to start up the old girl after a while lying idle. Turns over enthusiastically with the new battery. No spark to plugs. Tested ignition with volt meter, works OK, getting 12v to both sides of coil and out of the top of it. Spark plugs themselves are fine.
Must be the distributor? Not sure how to test that- any advise for this novice? Not sure how I go about checking the points.
Can I take the lead off the top of the coil and hold that to the chassis and turn over (ignition on) to double check that gives a spark to confirm it must be the distributor?
Thanks

(quoted from post at 03:39:30 06/11/18)
Can I take the lead off the top of the coil and hold that to the chassis and turn over (ignition on) to double check that gives a spark to confirm it must be the distributor?
Thanks

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Yes, you can hold the center lead near the engine block, while cranking with key on(and in NEUTRAL). This eliminates the rotor as a possible problem area.

But chances are that your condenser is bad or what always happened to me, the ground connection was oxidized. Try loosening the condenser screw, wiggle the connection and re-tighten.

One check that I always do, is crank the engine, key on, and watch the points. If you see a large spark, bad condenser or connection. If you see a tiny spark, it should be working.

Do check the points gap, around 0.015"

What tractor are you dealing with?

"I went to start up the old girl after a while lying idle."

On the wire from coil to side of distributor you should have near battery voltage with points open and near zero volts with points closed.

When a distributor sets for an extended time the points can develop a film on them that will prevent them from contacting. Take a dollar bill, fold it over a couple times and drag it through the closed points.

Points should likely be set at .020 and plugs at .025

Sorry chaps- 1948 TEA20.

You getting 12 volts on both sides of the coil to me says points have corrode and need to be cleaned or replaced. If the points where good you would get a lot lower voltage on the coil because the points would be grounding the system like they are suppose to do if they are working as they should be

(quoted from post at 08:53:56 06/11/18) You getting 12 volts on both sides of the coil to me says points have corrode and need to be cleaned or replaced. If the points where good you would get a lot lower voltage on the coil because the points would be grounding the system like they are suppose to do if they are working as they should be

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If the points are open, or oxidized, 12 volts on either side of the coil would be normal. If the points are closed, you should have ground (0 volts) on one side and 12 volts or whatever your battery is reading.

Agree with the rest, you are not connecting the coil to ground via the points.

Broken wire, oxidation on points or gap wrong.

(quoted from post at 03:39:30 06/11/18) Howdy Folks! I went to start up the old girl after a while lying idle. Turns over enthusiastically with the new battery. No spark to plugs. Tested ignition with volt meter, works OK, getting 12v to both sides of coil and out of the top of it. Spark plugs themselves are fine.
Must be the distributor? Not sure how to test that- any advise for this novice? Not sure how I go about checking the points.
Can I take the lead off the top of the coil and hold that to the chassis and turn over (ignition on) to double check that gives a spark to confirm it must be the distributor?
Thanks

Click to expand...

Well, getting 12 volt on both the terminals to the side of the center post )high voltage, does not have to be wrong if the engine is standing still. You need to crank it, a little by little, and see if the voltage on the distributor side of the coil drops. If it does not, then the point in the distributor does not make contact.

But, you say something very interesting I see no one has addressed, and that is that you say you get 12 volt on each side of the coil, AND on the top of it too. And that is not right. You should be getting nothing there. I would actually suspect a shortened coil. If the coil are good you should not be able to measure anything with a regular voltmeter out of the center post on the coil. If you hook it up, and if the coil is broken you might save the voltmeter and it will read nothing, and if the coil is good and you crank the engine you will fry the voltmeter and need to buy a new one. And with a broken voltmeter you will still read nothing.
What possessed you to measure the high voltage side of the coil ? You would need a very special equipment to do that.

If the coil is shortened, in other words it the insulation between the primary coil and the secondary coil is broken, you will read 12 volt out of the top of the coil. And if this is the case, you will not get any spark out of the spark plugs either.

Bill

Not too much joy I'm afraid gentlemen, still no spark but:
Have cleaned the points with mild emery cloth and checked the gap- 0.25mm as per manual
No voltage across the coil when the points are closed, 12V across the coil when points open
2.9 Ohms resistance across the coil, 5.2 Ohms out of the top (honestly I'm not sure what this means!)
No evident spark from the top lead of the coil if held to the block when cranking with ignition on
Just to clarify in response to Bill Brox, I haven't checked the HV of the coil whilst cranking, just with the ignition on (its designed to crank on the stick shift). Sounds a lucky escape
Ignition itself seems fine when checked with voltmeter

Any thoughts?! I'm none the wiser really and stumbling around as a electrics novice who wants to top the nettles- but tempted to get a new coil, condenser and maybe new points for good measure and replace one at a time and see!

Open and close the points by hand with the ignition on. You should both see and hear a spark. Do that carefully or you will find the spark in a way you will not like. Every time the points open you should get a spark from the center wire of the distributor cap. No spark at points means no spark any place else.

So.?...I replaced the condenser, points (checked gap), and coil and still no spark. Rotor arm looks fine, so does the spring bush that contacts with it. Loads of life in battery, turning over very well. Ignition switch works. Still no spark!!!!
Any thoughts???!!
Thanks- the nettles are growing!

Take the cap rotor and if it has one dust cover off. Next take the ignition side wire off the coil it is the wire not going to the distributor. with the points closed turn on the ignition and then touch the wire you took off to the coil. When you do that you should see a small spark. No spark means you have to clean the points. Some new points come with a coating on them that need to be cleaned off. If you have a spark then turn the engine till the points are open and try the wire to coil thing again. If you have spark with the points open you have a short some place. I've seen the insulator going into the side of the distributor go bad and short. Or the condenser wire is in such that it shorts. Or if you got the points from TSC I have seen those bad from the get go. I buy my points from O'Reilly's but NAPA also has good ones