Points are the most complex aspect of a basic engine tune-up, but they are essential. If your engine won’t start at all—or if it starts only with difficulty and runs poorly—and you are sure there is no problem with the fuel, ignition system, spark plugs, oil, or air filter, then it’s time to check (and possibly replace) the points.
To check and replace the points:
1. Remove the flywheel nut
First, block the flywheel in place. Either buy a flywheel holder, or wrap a belt around the flywheel to hold it in place.
If you have a Briggs and Stratton engine, chances are that the nut has a left-hand thread, so loosen it with a clockwise pressure. Once the nut is off, you can pull the flywheel.
2. Remove the flywheel
The flywheel is forced on to the tapered end of the crankshaft. Removal is best accomplished with a flywheel puller, which is commonly found in rental shops.
If you don’t have a puller, slip a pair of screwdrivers behind the wheel, opposite each other, and begin prying with alternate pulls. Pry in one spot and then turn the flywheel a quarter turn. Tap the flywheel very gently to create vibrations that will help loosen it. Keep repeating this process as you work your way around the wheel.
When the flywheel is loosened, check to make sure that the retaining key, which is in a slot between the crankshaft and the flywheel, does not wobble in the slot. If the slot is worn, take the engine to a shop and have the crankshaft replaced. If the key is worn, replace it yourself—but be sure to use a nonferrous key, not an iron or steel one.
Once the flywheel is off, you will see a plate covering the points and condenser. Remove the retaining screws and lift the plate off.
3. Check the points
The points are opened and closed by a lobe attached to the crankshaft (or, in some four-cycle engines, by a separate cam). Turn the crankshaft until the points are as open as possible. Use a feeler gauge set at the appropriate gap to check this. (Most small engine points are set at .020 inches.) Inspect the points. If they are pitted or if a little metallic hill has built up, replace them. (In an emergency they can be sanded down for one more day’s use.)
When you turn the crankshaft, if the points do not open at all, you may have discovered why the engine won’t start. If the points don’t open to the proper gap, the engine will run poorly. Usually when points don’t open properly—or don’t open at all—it’s because the fiber block, which rests against the crankshaft, is worn. If this is the case, you should replace the fiber block. Because the points are mounted on the fiber block and are sold with it as a unit, you’ll automatically replace both. If the fiber block is not worn, check the locking screw that holds the points in place. It may be loose.
4. Replacing and setting points
A set of points has one fixed side and one that is moved in and out by the rotating lobe on the crankshaft. The fixed point is moved away from the moveable point by an adjusting screw.
To take out the old points, first remove the locking screw. Then remove the wire that connects the coil to the fixed point as well as the wire from the condenser to the moveable point. An exception is the Briggs and Stratton engine, which has only one wire from the condenser to the fixed point.
Put the new points in place and fasten them down lightly with the locking screw. Turn the crankshaft until the tip of the lobe pushes the moveable point away from the fixed point as far as possible. That is the precise gap you need to set.
With the proper feeler gauge (usually .020) between the points, turn the adjusting screw on the fixed point until you feel a slight drag on the gauge. (On most Briggs and Stratton engines, the adjusting screw moves the condenser, which in turn moves the fixed point.) Check the gap by trying to gently insert the next larger size gauge. It should not slip between the points.
The condenser, which captures extra high-voltage electricity, is normally held in a retaining clip next to the points. Attach the wire from the condenser to the moveable point and the wire from the coil to the fixed point. Again, the exception is the Briggs and Stratton engine where the condenser wire attaches to the fixed point.
Before replacing the points’ cover and the flywheel, put a small dab of grease on the crankshaft to reduce wear on the fiber block. The grease often comes in the package with the points.