Linda asked someone to write up a wiki page for points.
I have this started.
haven't touched cleaning and adjusting on the peds yet or four strokers and the pics aren't added yet, but I'd like to hear input.
yes, it is a draft and i'm plenty willing to change it.
For the purpose of this audience this will be written for two stroke, single cylinder engines unless I note differently. I'll add four stroke and multi cylinder engines at the bottom.
Contact points, ignition points are the same name for an essential piece of the ignition system.
What is a set of points? or What are points? Simply put a set of points is an on/off switch. ( pic 1) But it is a very special on on/off switch. It is spring loaded and usually closed. It is opened by a lobe or bulge (cam) that spins around and rubs a block. That opens the contacts about .015 inch (check your manual for exact measurements) and then the spring closes them soon after. Electricity from your coils under the flywheel goes through the points and then to your coil. The coil converts the 6 or 12 volts into high voltage stuff and sends it to your spark plug. Each time the crankshaft revolves the points open and close and send that voltage on. Sounds simple enough, right? The engine may be spinning at 4,000 rpm or more. That's a lot of opening and closing. In a one hour ride, we expect these to operate 240,000 times. They also have to open and close at the right time. The spark must hit shortly before the piston reaches top dead center. That give the fuel/air mix a bit of time to start ignition and to produce it's power on the way down. This is called timing. If the timing is off, the plug can fire while the intake port is still open and blow smoke through the air filter. .You won't be likely to start it. If the timing is way off the engine may start, but actually be running in reverse.
Because of the many ways of setting timing on different peds, that will not be addressed here.
Points give us trouble in many ways. They get old and worn. They can get oily or wet. Oil and water can conduct electricity way from where we want it. and lose all power. The wires going to them shake and break. The wires may rub against the inside of the flywheel and ground out. Mounting screws can vibrate loose (rarely) and the block no longer rubs against the cam. The spring can break and the points won't close. Screws or clips holding the wire to the points can disconnect. When I see peds running without a cover over their flywheels I can't help but think. "One splash of water can stop that bike."
To make our trouble worse, they hide under the flywheel. To clean or adjust points you need to be peering in a tiny space with a flashlight, a feeler gauge, maybe two screwdrivers in a place lower than your knees.
It is never fun. A lift or a table can hold a ped high enough to make the height better, but most of us don't have those.
So how do you replace points? Sorry, you gotta take off the flywheel. Many kinds of pullers are available and there is also the dreaded rubber mallet method. Here is where Honda owners are happy folk. The flywheel is bolted to crankshaft. With simple tools it can be taken off to easily expose the points.
(pic 2) . On this NC50 you can see where the gap should be measured, how the wires connect and a place for adjusting them. Take the sparkplug out of the engine. Disconnect the wires (keeping track of which ones go where) Unscrew the screw(s) holding the base of the points in place. Install the new points, but don't tighten up the mounting screws. Add the wires to it and nudge the points over to the crankshaft.
Hope you don't own a Garelli. Garellis have the cam for the points inside the flywheel (pic3)so they can't be set until the flywheel is in place. Motobecanes have a cam that is a separate piece (pic 4) that is mounted on the crankshaft. It must be in the right place or you will be in serious trouble. Ok, you can now turn the engine by hand (aren't you glad you pulled out the spark plug) Make sure you are turning it the same direction it runs. On the Honda Expresses with the tap starters you can have serious trouble if you turn them the wrong way. As you are slowly turning that engine you can see the cam on the crankshaft start to push the points away. You want the farthest place that the cam will push to be resting against the rubbing block. Gently push the assembly into the cam until the points open. Now grab your feeler gauge (pic 5), and get ready to put it in the gap. Slightly tighten the assembly mount. Open the points by hand and rest the feeler gauge between the round contacts (pic 6). With one hand you can use a screwdriver in the notch in the points to move the mounting plate to exactly where you want it. With your other hand drag the .015 (or your spec.) blade through the contacts, moving the first hand until there is barely a drag on the feeler gauge. With your third hand, tighten down the mounting plate. Again on the Garelli, the adjustment must be done with the flywheel in place working through the grooves. Check your timing. Cover everything up.
Put your spark plug back in, put away your tools and ride.