Small four-stroke, single-cylinder engines can typically be found in lawnmowers, compressors, water pumps and generators. Simple in design and function, they can produce a lot of work for pennies in gas. Other than regular maintenance, nothing much happens to these engines to cause major problems. Although the timing features can not be adjusted on single-cylinder, four-stroke engines, there are instances where the timing can be reduced or thrown off dramatically, requiring repair and maintenance.
Place the engine on a solid surface where it will not slide. Use a socket and wrench to remove the main engine cowl. The cowl usually has three bolts that secure it, and it sits on the side or top of the engine. Pull off the cowl. Inspect the crankshaft for a ratchet device connecting to the pull start, or a socket that holds the flywheel in place.
Use a hammer to tap the ratchet device counterclockwise to unscrew it. Use a socket to remove the flywheel nut, if it has this fastener. Do not remove the flywheel yet. Use a socket to remove the spark plug from the engine. Turn the flywheel by hand while you hold your finger over the spark plug hole. Stop when you feel air pressure on your finger.
Inspect the flywheel and magneto. The magneto looks like a coil with two prongs extending to the edge of the flywheel. The flywheel has a magnetic pickup on its edge that should align with the end of the magneto prongs. If it does not align, the timing has slipped. To confirm it, rotate the flywheel back and forth rapidly. If it moves on the crankshaft, the flywheel has sheared the key or slipped on the shaft.
Place a flywheel puller over the flywheel, and hook the puller prongs on the back of the flywheel. Place the puller shaft in the recessed end of the crankshaft, and turn the puller handle clockwise until the flywheel comes off. Inspect the crankshaft keyway for damage, and remove the damaged key. Place a new key in the crankshaft keyway slot. Tap the key with a hammer to set it firmly.
Use a screwdriver to unscrew the silver, circular case that holds the points and condenser. Loosen the one adjusting screw on the points. Remove the other screw with a screwdriver. Remove the two small spring clip wires from the points. Use a screwdriver to remove the single screw that holds the condenser in place. Discard the old points and condenser. Slip the new points in under the adjusting screw, and insert the other points screw. Tighten both screws with light pressure only.
Place a new condenser into position, and tighten the single screw with a screwdriver. Attach both small wires in the spring clip. Use pliers to turn the crankshaft until the small cam lobe on the crankshaft rests against the rubbing block connected to the points. Refer to your owner's manual for the correct gap measurement required for your points setting. For example, it might be .020. Select the correct blade and place it between the contact pads on the points.
Place a screwdriver in the points adjustment slot and turn it back and forth to close or open the points. Once you have the points pads closed on the proper blade thickness, tighten the points adjusting screw and then the mounting screw. Replace the points cap and tighten the cap screws with a screwdriver. Set the flywheel over the crankshaft and push it down over the keyway as far as possible. Screw the ratchet device back down, or the flywheel nut and tighten it with a hammer or socket.
Insert the spark plug and screw it in with a socket. Reconnect the spark plug wire. Place the engine cowl back on the engine and insert the bolts. Tighten the bolts with a socket. Pull the rope starter to test the engine.