Ford tractor distributors electricity 101

One of the things I like about these old tractors is being able to fiddle with things like points. These old engines will usually start telling you they need service, LONG before they quit running. I get emails all the time from people that start out with something like, "my tractor was getting harder and harder to start, now it won’t start at all". HEY! Why let an obvious problem go for weeks or months? Why not fixt it before it’s snowing an inch an hour? Well, that is nice in theory, but out in the real world with professional procrastinators like me, maintenance often takes a back seat to essential activities like drinking beer and throwing darts.

Modern cars have spoiled us. We are losing the ability to pay attention. "Getting harder to start", means it’s PAST time for some maintenance. It is often imposible to say "the" problem is air cleaner, points, condenser, plugs, wires, cap, ignition switch, etc. By the time I get a no-start tractor running again, I’ve fixed several things that could have been "the" problem. If you suspect points, it only takes a minute to check them on a side distributor engine. Maybe 2 minutes for a front distributor. You can try popping the front cap and using a mirror to get a look, but I’m going to just pull the front distributor, and take it to my workbench. If I’m working on a side distributor, I get something to sit on, or sit on the tire.

You should have an ignition point file in your tool box, on the tractor. This is a small metal file that is easy to slip between the points. If the points look rough or wet, just running the file through them is often enough to get a tractor started. Mark it on your list to properly service the distributor as soon as you can.

When checking the points, grab the end of the distributor shaft and see if there is any side play. These engines are 50 to 70 years old. It might have been a LONG time since the last distributor rebuild. New distributor bushings only cost around $10 each and most anyone can replace bushings. If the shaft is badly worn, you might need a new one. That’s a little more expensive. If rebuilding is beyond your ability, rebuilt or new distributors are available. A sloppy distributor shaft is nothing but trouble. It needs to be fixed as soon as possible. SETTING THE POINT GAP

The correct point gap for a front distributor is 0.015". For a side distributor it is 0.025". After setting a million sets of points, I can tell just by looking at them if they are close enough to run, but I’m still going to use the proper size feeler gauge to check them. The wire type gauges are usually easier to use, but a flat type can be just as accurate.

Looking at the guts in the distributor, the points are bolted to a flat plate under the rotor. The rotor should easily pull straight off. If this is a side distributor engine, watch out for a small spring clip in the bottom of the rotor or it may stay on the shaft. Don’t lose that clip! The spring clip is what keeps the rotor tight. The distributor shaft also has a flat spot that corresponds to the hole in the rotor, so the rotor only fits one way.

NOW, if you have the front distributor on your work bench, ignore this paragraph. Make sure the tractor is in neutral, then bump the starter until it stops with the points open. It is ideal when the high point on the distributor cam stops right on the rubbing block of the points, or a little bit before is ok. The mechanical advance in the distributor will allow us to turn the distributor shaft if it stops just a little short of the peak. The distributor has a mechanical advance mechanism under the plate. No need to remove the plate to look at the mechanism, unless you are rebuilding the distributor. The advance mechanism does allow the distributor shaft to be turned a bit to line up a point on the cam with the rubbng block of the points.

With the front distributor, we avoid all this messing around and just turn the distributor shaft anywhere we want it. Once we have the rubbing block sitting on a point of the distributor cam, check the gap between the two pieces of contact material. What we are measuring is the maximum distance the distributor can open the points as it turns.

If we are replacing the points, they are held to the plate in the distributor by a screw at each end of the fixed point bracket. Ignore the screw in the middle of the point strap on the front distributor. That is a special eccentric screw that helps adjust the points. The side distributor does not have this simple eccentric screw adjuster, the side distributor has a notch in the points that can be pried with a flat blade screwdriver to help set the gap. Once we have the new points in place, and the attaching screws barely loosened, we will see how the eccentric helps.

Before we get all excited and install the new points, look carefully at them. Many of the replacement point sets are not made very well. Look at how the two pieces of contact material come together when they are closed. Do they come together square and centered? If not, you may need to bend them slightly to correct the error. Sad that quality has deteriorated to the point we have to tweak new parts. Be careful where and how you bend them. I clamp the base in a vise and use a short pair of needle nose pliers to carefully bend the fixed side mounting tab into alignment. If the points are not aligned properly, there will be less surface area to transfer current, and they will soon be pitted and burned. Finally, I make a few passes with a point file between the two contact faces to make sure they are filed parallel, and to remove any manufacturing glaze that would prevent them from working.

Now, install the points in the distributor, but leave the mounting screws just barely touching, so the plate can still move. On the front distributor, the eccentric bolt can now be turned to "set" the proper gap. With the side distributor we have to manually pry the points until the gap is correct. Tighten the screws and re-check the gap. It probably moved a bit. Loosen the screws and try again. If the points closed a bit, try starting with a little too much gap. It often takes several whacks, but this has to be done correctly. Almost right, isn’t good enough, if we want the engine to run well.

If the points screws are stripped and will not hold tight, the fix is to replace with a slightly larger diameter screw. The replacement will be a very short length #8-32 screw. That length should not be more than 3/16" or it will interfere with the rotating advance weights below the top plate. If your top plate already has the larger screws, it’s time for a new top plate assembly.