"..with 9000 miles on my 500 I have yet to check the points or change the plug. If it aint broke leave it the hell alone!!!"Normally, I couldn't agree more, but I'd change that leave it to check it once in a while, anyway. Or better yet, learn to listen to your engine at all times, and NEVER run it with detonation! (Also called spark knock, pinking, or ping.)
When I first started riding motorcycles, more than a few of my friends were having two basic problems:
1) Colliding with cars
2) Blowing holes in pistons
The first I took care of by analyzing every accident I heard about. (And a few close calls of my own.) I soon concluded that motorcycles are less than invisible to car drivers (we appear to them as holes of opportunity in the traffic stream composed only of other cars) and that one MUST EXPECT any and all cars to cut in front of us, or run into our sides, or rear-end us, at all times. I've been riding completley paranoid since '56, and have yet to (knocking furiously on wood.....)
The second took a little longer. The popular belief at the time was that so-an-so is just really bad, and he rides so hard that the blows bikes up all the time. What a guy! This never happened to me, but only because I took the advice of the various manuals of which I was able to get ahold, and checked my timing regularly. I soon got to be able to recognize the sound of a retarded single, and of course the sound of "ping" which tells us it's too far advanced. For those who have yet to develop the ear, I'd strongly recommend checking timing on a regular basis. Too retarded will burn the exhaust valve out of the thing, and too advanced will blow a hole in a piston. Compared to the little bit of trouble it is to check your timing once in a while they're both fairly catastrophic events.
It was at first only coincidence that some of my friends were blowing their bikes up and I wasn't, but sooner or later I figured out that it had been advanced timing that had taken those pistons out, not hard driving. They had been, of course, used bikes, and the DPO's had likely sold them after tweaking timing unsuccessfully. Bummer!
So, now to today's lesson:
There isn't a lot to checking your timing - in most cases, you won't have to adjust it, and soon you'll get to know just how often you'll need to do it, and begin to develop an ear for the "snarl of a well-tuned single," a quote I still remember from an early _Cycle_ magazine - a road test of a Matchless scrambler, I think it was.
What lights up the compressed mixture is the spark plug, and the firing time, relative to the position of the piston, is controllable by adjustment of the spark advance - setting your ignition timing. The spark fires, in points systems, when the points open - they close soon after, and what happens during the time they're closed is another story, beyond the scope of this lecture. What's important to us just now is that each time they open, a spark is sent to the plug.
Three Possiblities:
(1) Put the bike on the center stand, or otherwise raise the rear wheel. (Milk cartons are the time-honoured way to do this for the center-standless.) Remove the spark plug, being careful first to clean the area around the plug hole to avoid ingestion of foreign object (rocks, mud, beercaps, etc.)
2) Prepare the timing stick. Take a 6" piece of straight coathanger, welding rod, or similar material. With the bike in top gear, insert the wire through the plug hole, as close to straight down as you can get it. The rotate the rear wheel in a forward direction until the wire is forced upwards. When it gets as far up as it gets, rotate the wheel back and forth until you get the "feel" for Top Dead Center-" you'll soon figure that one out. Then, make a note of a spot on the timing stick that corresponds to some spot on the cylinder head - the top rim of the spark plug hole is a good one. Mark this with your thumbnail, withdraw the timing stick, and mark this TDC point with the file or hacksaw blade. (Or you could be using a Popsicle stick and a pencil, it's not critical.)
3) Now, all you need to do is to mark the proper advance distance on the stick, below the TDC mark. Spark advance specs are given as before TDC, either in degrees of crankshaft rotation, or in actual piston travel distance - the spec we'll be using here. You'll need to get the distance from your manual, or a reliable source. Using a ruler or scale, mark this distance on the stick, and you're ready to check your timing. You may want to keep the stick in your toolbox for future reference.
1) For this, you'll want to use the test light. When the points are open and the ignition is on, there will be a voltage present across the points. When the points are closed, this voltage will drop to 0. So you want to connect one side of your test lamp to the wire from the coil to the points, and the other to ground (the other side of the points.) When the points open, the light will come on, when they close, it will go off. Move the wheel back and forth around TDC with ignition on and light connected, to verify that this is happening.
2) Now it's time to check with the timing stick. Move the wheel BACKWARDS until the piston is an inch or so down. With ignition still on, push the timing stick down onto the piston crown, (vertically, remember!) and rotate the wheel forward until the light comes on. If the advance mark on the timing stick passes your reference point at that exact position, Bob's yer uncle. If not, you'll have to adjust the timing until it does. Don't forget to turn off the ignition after checking!
Once the gap is right, it's time to move your breaker plate. Loosen off the holding screws so that it will turn freely - but not too freely. If the plate is too loose, it will move , once you've set the timing, when tightened, and you'll have to do it again.
2) Set the piston to the advance point. Run the wheel back past TDC, then, feeling with the stick, forward again until you reach the advance point.
3) Now to set the Breaker Plate. First, you'll need to make sure that your centrifugal advance mechanism is working. If you attempt to twist the rotor/cam shaft, back and forth, you should find that it will move a bit. This is normally accomplished by the springs working against a set of centrifugal weights behind the points plate. You need to set the timing in the full advance position - with the cam rotated full in the direction of rotation when the engine is running.
Power up the ignition and connect the light. Then, with the rotor in the advance position, (you'll have to hold it against the return springs as you have a friend rotate the rear wheel) rotate the housing in the direction of lobe rotation until the light goes on. Then rotate the housing AGAINST the direction of lobe rotation until it just goes out. This is the point at which the points will open in normal operation. Once you've done this, tighten the set screws.
4) Now, check it by rotating the engine through two revolutions in a forward direction. Pull out the timing stick, so you won't bend it, until the second time the piston is on it's way up. As the advance mark hits the spot, the light needs to come on. Keep doing it till you get it right; it'll soon be second nature. Like most things, it'll take a half a day the first time, but will soon be doable in just a few minutes.
Once you've set it spot-on, start listening to your bike. Try to develop an ear for retarded timing. As for advanced timing, read pingtime.htm on this website for a detailed rundown on setting timing dynamically - the best, but more subjective, way to do it.
The very earliest points-fired Brit twins didn't have this variable pointset feature. For these, you have to vary the point gaps a thou or two in either direction until they both open at the same precise instant relative to piston position. Then check with the strobe. Use of a stroboscopic electronic timing light is recommended to check that both plugs show the same advance before ping-timing. Then, once you've got it ping-timed, check the timing with the light at ~1500 rpm and make a note of where the mark flashes. You can then use this reference to check your timing in future, to duplicate the ping-timing you found so successful. By the way, if you find your timing light is flashing all over the board, and it's the type that requires a 12V supply for power, use a battery other than the one on your motorcycle - they sometimes pick up spurious signals from the alternator system.
I hope this helps. All this typing was worth it if it saves just one piston! Happy riding!