Wisconsin S-7D Motor refusing to start

No such thing as a silly question!

To check the compression: one generally uses a compression tester, which is basically a pressure gauge. You can do it without a gauge by removing the spark plug, and holding your thumb over the plug hole while cranking the engine. The engine should rather strongly push your thumb a bit away from the hole. The pressure should be around 80 pounds per square inch or more, but there won't be a lot of volume, so your thumb won't leave your hand. The engine should push your thumb a bit so the compressed air escapes "with authority". (I would ground the spark plug wire to the block to prevent electrical damage to the mag, since creating spark voltage with no place for it to go can do damage to the mag.) A lack of compression will not cause pressure to move your thumb, and has several causes. Most likely is valve leakage. Before taking the engine apart, you might try squirting a bit of oil in the plug hole. That will temporarily seal the rings and boost compression if the rings are bad. I'd to that second. In other words, thumb test your compression, then squirt the oil in and check it again. An improvement indicates leakage around the rings. That might mean worn rings, or just that the rings are dry from sitting around so long. If you notice increased compression, try starting the engine again. Perhaps the increase in compression will be enough to get it running.

Top Dead Center is a position, not an object. TDC refers to the position of the piston in the cylinder bore. When the piston is as high as it goes in the bore, and the crankshaft is centered right under it, that is TDC. If you can see the piston when looking in the spark plug hole, you can see it moving up and down while the crankshaft turns. When the piston is at the top, it is at or near TDC. Most engines have a mark on the flywheel to indicate TDC, since you can't see the crankshaft itself to see when the crank journal is directly centered under the piston.

A fairly accurate means of finding TDC if it's not marked on the flywheel is to observe the piston's travel. Turn the crank until the piston just starts to move down, and mark that point on the flywheel, next to something that is stationary. Then turn the crank the opposite way, and note when the piston starts to move down again. Mark that position. TDC will be between those two marks. This is just an approximation, but may be helpful in determining when your spark should occur.

In your case, I would expect to hear the magneto impulse coupling snap when the piston is at or very near the top of its travel.

I hope I haven't confused you further! Please feel free to ask whatever questions come to mind. That's why we're here!

I don't think you have a magneto, you have points-and-coil. Forget what was said about the impulse coupling.

Nice pictures!

The cylinder that the plug wire goes into is your coil. With the points open, there should be battery voltage on both small terminals of the coil. With the points closed, there should be battery voltage on one terminal, and close to 0 volts on the other.
The position of the points is key to this check.

The coil will fire when the points open. You set the timing so that the points are just opening at the correct time, which is somewhere near TDC. You may not be able to adjust the timing directly, the points gap will do that for you.

Unless you have the correct specs, I'd set the points to .025 inch at their maximum opening. The point gap will also affect the timing. The adjustment slot fig. 10 refers to is how you adjust the point gap with a screwdriver, after loosening the lockscrew a bit. There may be a data plate on the engine with the points gap listed.

You will have to turn the engine by hand until the points are open as far as they'll go. If they aren't around .025 inch at the max opening, adjust them.

I don't know about the pin, but if it's opening the points, it's doing the job.

I got totally confused reading this, so I'll offer this advice: Take a voltmeter, clip the (-) to the negative side of the battery itself. With your ignition switch on, you should have B+ (battery voltage) on the + side of the coil all the time. With the points open, you should have B+ on the - side of the coil. With the points closed, you should have close to 0 volts on the - side of the coil. The diagram TOM603 posted is correct.
If you don't get these voltage readings, post what you get and where. This is not rocket science, but does need a logical approach, and we'll help as we can.

The condenser should be grounded to machine ground.

Reading your post #38, it appears that the points are not grounding the coil primary circuit. When the points close, they ground the coil primary circuit. When they open, they break the circuit, inducing the high voltage out of the coil secondary.

The 12v on the coil secondary is also confusing. The coil body needs to be grounded to the engine, as do the condenser and one side of the points.

Please post the voltages at the various places I mentioned, and we'll go from there.

Okay, I think I have a handle on it now….

The points are shown in pic #36, bottom photo. They are the "switch" that turns the current on and off through the coil by grounding the - side of the coil, then breaking the ground path. That silver rod that comes out of the engine case should open and close the points as the engine turns. Watch it, and you'll see how the points open and close.

The - side of the coil should attach where you have the black clip lead. The condenser appears to be connected correctly: the wire should attach to the points lead/spring, which it appears to do, and the case of the condenser is grounded through its clamp. The wire should NOT be grounded. It should go to the connection for the points, as it seems to do in the picture.

Try this: turn the engine by hand so that the points are not closed (not touching each other). Connect the black lead in pic #36 to the - side of the coil. Turn the switch on. You should have B+ at the black lead. (If you don't, let me know. That's another issue we can correct.) With an INSULATED screwdriver, short across the points a few times. You might see a small spark at the screwdriver, but you should see a spark at the plug.

We're closing in - almost there!

Try spraying some carb or brake cleaner in the intake and starting it. If it runs for a few seconds, you know the mechanics and electrics are okay.

Is the choke closing? You didn't mention that in your last post, I haven't reread the others.

Do you have adequate compression?

Have you checked to see if the flywheel key is not sheared, even partway?

I am assuming that your spark plug is in good shape, and firing.

Have you checked for spark with the engine cranking?

This is a puzzler…One of the three is missing -
1) spark at the right time
2) enough compression
3) proper fuel mixture

You pretty much rule out the fuel when you spray into the carb, so that leaves #1 & #2.

I'm at a loss except to suggest that you approach this engine like you've not seen it before, and recheck everything as if you hadn't worked on it at all. Assume nothing.

I do have one suggestion - recheck the points gap - if the gap is way off, you'll get spark, but the timing will be off. It's worth a shot, and easy to do.

I know how frustrating this can be. I spent all winter, on and off, trying to start an old Farmall Cub. Everything was there, but it wouldn't start beyond one pop that would kick the starter out. It turned out to be a bad condenser that would allow a weak spark at cranking speed, and no spark above that. A new condenser, and it starts great. I have never run into a weak condenser in the 50 years I've been playing with small engines. There's a first time for everything. Hang in there, you'll get it! :fing32: