definitions of motorcycle

If you have a car engine, you can get a rebuilt engine from a lot of different places. You can get a "Short Block" without a rebuilt cylinder head or a "Long Block" with a cylinder head. You can do the same with any of the lawnmower type, small engines. But when you get to motorcycle engines, none of these options are available. This is because they just don't make that many of each type of motorcycle engine. They will make millions of each type of car engine, but only, maybe 100,000 of each type of bike engine. I guess that is the price of performance.
Because of this you must rebuild each engine by ordering individual parts. Oops, I forgot Harley is now offering rebuilt engines for a price, and a place called PMC has just started to offer selected rebuilt engines. Still, on most engines, you just don't have a short or long block available.
Here is what I think is right for a rebuild and why.
On four cylinder bikes, a top end job just isn't economically feasible unless it's a very new bike, you are hopping it up, or it is a restoration. If it's just a bike to get to work on, junk it out and buy another bike.
A four stroke engine top end rebuild would consist of the following:

New oversize pistons, rings, wrist pin, and clips

Bore cylinders

New Top End gasket set

New Valves both intake and exhaust

New valve seals

Check valve guides

Measure and/or test valve springs

Cut valve seats

Clean engine parts

New cam chain- A lot of people forget this one. If the chain is stretched it will effect the engine timing.

New cam chain sprockets if possible.

Check Cam chain Guides and adjuster

Take a close look at everything as you take it apart. Especially bearings, like on the cam. If things look worn they probably are.

If you just take the head off, say to fix an oil leak. You better be careful and not disturb the cylinders or you will have an oil leak there too. Gaskets get hard over time and once you break them loose from the metal, they will not reseal well.

If water cooled, always use anti-freeze and not straight water. If you use water and forget to change to anti-freeze, come winter, the water will freeze cracking the cylinder and/or block. A single cylinder, two stroke, engine top end rebuild consists of:

New oversize piston, rings, wrist pin, wrist pin bearing, and clips

Bore cylinder

New top gasket set

If you have a power valve, you may have to grind it a bit to clear the new piston and rings.

If you have water cooling, always use anti-freeze and never straight water. If you use water and forget to change to anti-freeze, come winter,the water will freeze cracking the cylinder and/or block. A four stroke bottom end job just isn't economically feasible except perhaps on a single cylinder. On most Four cylinder bikes you would be talking a lot more than the bike is worth. With the exception being Harley Davidsons and perhaps other big bikes that hold their value (Ducati, BMW, Moto-Guzzi etc.).

If you do go into the bottom end check everything. Like gears, shifter forks, bearings, etc. Now is the time to fix it, while you are in there.

Replace rod bearing and maybe the whole rod

Replace the primary chain if it is at all worn

Replace primary and cam sprockets if worn

Replace all seals, o-rings, and circlips

Replace the crank main bearings

New bottom end gasket set A two stroke bottom end job consists of:

New rod, crank pin, crank bearing, crank washers (2)

New crank seals (2)

New crank main bearings (2)

Complete gasket set

Labor to press the crank apart and together and to true it.

New crank and clutch lock washers and it's a good idea to replace all the other seals, (kick starter, counter shaft, shifter, etc.) o-rings, and circlips. A multi-cylinder, two stroke, bottom end job isn't economically feasible unless this is a classic restoration and you have lots of money. If it's just a bike to get to work on, junk it out and buy another one.

If you do go into it replace all seals, o-rings, circlips, and gaskets.

Replace all main bearings A good tune-up is simply resetting all the things on a bike that wear and change, back to the original factory settings. You will find that a simple tune-up will cure a lot of problems. ALWAYS do a full tune-up BEFORE you start ripping things apart.
A four stroke, electronic ignition, bike tune-up consists of:

Adjust valves.

Some bikes have hydraulic valve adjusters and don't need regular adjusting.

Lube all cables

Lube any grease fittings you can find with a grease gun

Clean or replace the air cleaner

Adjust front brake cable

Adjust rear brake cable or shaft

Adjust rear brake light switch.

Adjust and lube chain

Install new spark plugs and properly adjust the gap

Check spark plug caps

on all cylinders and keep a record of it.

for a points ignition bike add:

Adjust or renew points and retime engine For a two stroke lose the valve adjustment and add:

Adjust oil pump You will notice we don't just replace everything without a good reason. On a car rebuild you replace a lot of stuff because new doesn't cost much. Like valve springs. A set for a car may be 10-20 dollars. on a bike they are 5 bucks each... 2 for each valve... 8 for each cylinder... 32 for the engine. 5 times 32 is an extra $160. A lot of money, at least to me ! So we measure them and reuse them if we can. So it is with everything else.

motorcycle pistons

Pistons and Cylinders are pretty straight forward. After you take the head off try to move the piston, sideways, in the bore. There should be almost no movement. look at the cylinder. If there is an obvious ridge at the top of the cylinder and you can feel it with your finger, and there is piston movement sideways, you are going to have to bore it oversize. The factory oversizes are in quarter millimeter increments. Like .25,.50,.75,1.0 and the like. .25 mm is about .010". That's enough to clean up the bore, but it is not enough to increase the size of the engine by much. If you are unsure, measure the diameter of the bore and the diameter of the piston with inside and outside micrometers. Measure the piston about 1/2" up from the bottom of the piston skirt. Now measure the cylinder bore in several places at right angles to each other. Subtract piston diameter from the biggest bore diameter. This gives you the piston clearance. Piston clearance varies due to a number of factors.

1. Diameter of the piston.
2. Type of metal the piston is made of.
3. Is it a cast or forged piston.
4. Is the engine air or water cooled.
5. Is the engine two or four stroke.

A small (50mm bore) cast piston, 4/stroke may have half a thou (.0005" or .0127mm ) piston clearance, while a big, forged piston, 2/stroke (73mm, 2.874") can need .003" (.075mm) or more. You will need a shop manual to find the clearance for your bike. Now this is the minimum. What is the maximum ? I once had the exhaust off of a 400cc 2/stroke single, and I was able to slip a .020" feeler gauge between the piston and cylinder. Why did I have the pipe off ? The guy wanted me to check the pipe out. I found several, large, rubber, air cleaner box mounts in the pipe ! The guy said he had never had the pipe off. The bike ran for several more months before the piston skirt broke. Bottom line, get a shop manual and get the right clearance. If it is an after market piston, use the piston manufacturers clearance recommendation.
If your old piston is within spec, and you want to reuse it, you will need to measure the ring side gap. Side clearance (gap) is measured with a feeler gauge, with the ring in it's groove in the piston. Just try to fit the feeler gauge between the ring and the top or bottom of the groove. They can be .001" to .003"(.025mm to .0762mm, check the manual). If you are using a new piston and rings you do not have to check this. If the gap is too much, even with new rings, you will need to replace the piston.
Everybody seems to think a new set of rings should cure everything. I wish it was true... but it's not ! I would say 95 % of the time, on a dirt bike, you will need to bore it oversize. Sometimes, on a big street bike, the pistons will be within spec, but on most of the dirt bikes you are going to have to bore it.
It is best to have the cylinder bored on a boring machine. I have honed them as big as .040" over and I held it to spec on taper and out of roundness, but it took forever. Now, if I go bigger then 1/4mm or .010" I like to bore them on a machine. If you do try to hone them be sure to use a good hone like a Sunnen or Ammco. You will have to measure the piston and then bore the cyl to fit. Do not bore the cyl unless you have the piston to measure. If you do, the clearance may be off.
Remove the circlip and push the wrist pin out with a screw driver. You may lightly tap it but if the pin is in too tight, you will need to pull it with a wristpin puller.
If the piston has seized and smeared aluminum on the cylinder you will need to remove it before you measure it. You can do this with Muriatic acid. Just take medicine dropper and put just a few drops on the aluminum that has been smeared in the cylinder. The acid will eat the aluminum but will not hurt the steel of the cylinder. DO NOT GET THE ACID ON YOU . If you do get it on yourself, water and baking soda will get it off. Also don't get it on any aluminum unless you want that aluminum eaten up ! You can get Muriatic Acid at any home improvement store. They sell it buy the gallon, which will do about a billion cylinders. I'm not sure what they use it for... swimming pools or something.
If you have a 2/stroke, be sure to look at the top of the piston. If it looks like a rat has been chewing on it watch out. It means that the bearings in the bottom end are starting to go. If you put in a new piston it will just be ruined as more bits of bearing shed by the lower crank and rod bearings. The cure ? Rebuild the bottom end.
Be sure to check the cyl for any rust pits. If there are any you will need to bore the cyl to a bigger over size to get rid of them. If you are restoring a machine, you will find these rust pits are wherever the rings stopped in the cyl. A lot of water is created during combustion. Supposedly, about a gallon of water for every gallon of gas burned. Some of that water tends to collect around the rings.
When you get your cyl back always ask if they cleaned it. Most places do but, you never know. To check, take a clean rag, put some fresh oil on it and wipe the inside of the cyl with it. If it brings up any dirt, take your cyl and wash it in lots of hot soapy water. Immediately dry and oil the cyl so it will not rust.

motorcycle system

Electronic Ignition... so easy to get to, so easy to test... so easy ! I hate electronic ignition systems. At least, I hate to work on them. I wish I could tell you I know everything about motorcycle electronic ignitions, but, well, after working on these things since they first came out I can categorically state that I don't know 'nothing about them. So I'll just ramble on about them for a while, and if you read real carefully, you will know as little as I do !
Most Electronic Ignitions have four parts that can fail. trigger (pickup) coil, a source coil, a CDI unit (Black Box) and an ignition coil. The trigger coil tells the black box when to trigger the spark. It does this when a small magnet on the flywheel passes the trigger. The source coil produces the power. The black box coordinates everything and tells the ignition coil when to fire the spark plug. This is for a magneto and requires no battery, as the power comes from the source coil. Battery Ignition CDIs use the battery as a power source. The battery is then recharged by the charging system.
Now, when I say CDI I mean Capacitor Discharge Ignition, but I am also lumping in all types of ignitions that don't use points. Each manufacturer has their own design and way of thinking. However, they all seem to have those four parts. Trigger coil, source coil, black box, and ign coil. Usually, they give you specs on the trigger unit, source coil, and ignition coil. Sometimes, they give specs on the CDI box too. These specs are given as resistance values in Ohms. That means we can test them to see if they are good... sort of... most times... maybe ! Some manufacturers also give values for the black boxes too, and some don't. All this means these things are very hard to test accurately. Fortunately, most of the electronic ignition units are quite reliable and require no service, but this plus turns to a minus when they do go bad. They are very hard to trouble shoot. To top it off, most motorcycle CDIs are expensive to replace, and when they go out, the bikes are too old to justify the expense of replacement.
They say electronic ignition doesn't change once it is set. BUT, IT DOES ! Sometimes, it will change as it fails. This can give some pretty weird running. It can also cause the engine to overheat and seize. This is something to remember when you rebuild an engine that blew up for seemingly no reason.
OK, we can use an ohm meter to check most things except the black box, and sometimes, even the black box... If we are lucky ! Well, maybe things tested Ok. You have to remember, on all electrical things, they test either bad or they might be good. There are a number of very expensive testers out there, and they all claim to work great. But do they ? Let me tell you a story. I once had a snowmobile come in which would die (no spark) after 5-6 minutes of running. I had factory specs on everything including the black box. Everything tested OK, even when hot. Long story short, I finally ended up talking to the owner of a business that made aftermarket, replacement, snowmobile CDI boxes. He told me all the factory specs were wrong, and gave me some new specs that he said sometimes worked and as he was very knowledgeable about electronic ignitions I asked him what tester he used. He told me he had tried them all and none of them worked. He said for each new CDI box design his company bought an engine, and modified it so they could run it with an electric motor. They could then test the black boxes by substitution. Customers could send in their factory CDI boxes and he could test them to see if they were good. He said they had a whole warehouse full of these modified engines. This was back in 1988-89. I like to think they have something better now... however, I still can't afford a tester other than an Ohm meter.
The reason I'm telling you all this, is to give you an idea of the amount of hassle these things can be. Many times I've read factory bulletins telling their people in the field to be more careful. They're sending back, under warranty, too many "bad" boxes that turn out to be good.
All right, we have no spark. Check the resistance, in Ohms, of the Trigger coil, Source coil and Ignition coil. If one is out of spec, replace it, but first check all the plug in connectors. Check and clean all the ground connections and make sure the kill button is working right too. Also, remember some bikes have safety kill switches at the clutch lever, the side stand, and who knows where. Look for them and make sure all of them are working right. Check each Ohm reading several times and remember most specs give a temperature to check at, usually 70 degrees. So don't leave the bike out overnight at 30 degrees and expect to get an accurate reading. Sometimes there will be a spec for the black box, and sometimes not. Here are the specs on a Kawasaki Vulcan. Others, if they give any, look similar. As you can see, there are a fair number of tests to perform. Maybe this is why a lot of manufacturers don't give any specs. Honda used to give specs, but it seems they don't anymore. Yamaha doesn't give any. Kawasaki and Suzuki both sometimes give specs and sometimes defer to special factory testers. Others ? You will have to look in the shop manual.
The shop manual will give you the color of the wires to test and the correct resistance too. If everything is within spec, recheck all the connectors and the grounds. If all is OK the only thing to do is replace the black box. Sometimes you can get the part off a working bike and substitute it for the part in question. Most times this can work pretty good. Other times the bad part can take out other good parts. The reason this can happen is because these systems produce very high voltages. That voltage has to go somewhere. Sometimes it can burn it's way through the side of the plastic case. The good news is that this is quite rare in most motorcycle systems. Don't you love the way I use most and sometimes and might and maybe ? There's good reasons why electrical parts are sold with no warranty.
Another thing to check is the air gap between the trigger and the magnet on the flywheel. Usually this is done with non-metallic, brass gauges. You can also use a piece of plastic of the right thickness. That thickness is usually .005" to .010". Try to get the parts as close as you can, without them hitting.
Sometimes, there is no separate trigger unit. Everything is in the coils or the black box. The circuitry reads the voltage rise and triggers the spark at the right time. They do have little ignition units that are used on lawnmowers and small engines. They tell me some of these units can be used on motorcycles. I've never used them on a bike, but they do work on other small engines.
Most Dirt bikes are a CDI magneto, and do not require a battery. Most street bikes are a battery charged CDI, and need a fully charged battery. That battery also has to run the starter, lights, radio, and other stuff in addition to the ignition. Different things require different power requirements from the battery. We think of the battery as supplying a steady 12 volts and it should. But, things can vary. What does all this have to do with electronic ignition ? Most electronic ignitions require a full 12 volts to give out a good spark. If you let the bike sit a long time or the battery is weak, you may not get a full 12 volts. Now the starter may spin just fine, but the starter requires amps more than volts. Think of it like this. Amps are volume, volts are pressure. Amps won't jump a spark plug gap and volts won't spin that starter. At least they won't in the numbers that we deal with. Anyway, the starter is spinning but the ignition is not getting enough volts to fire the spark plug. The moral ? Make sure you have a good, fully charged battery in the machine before you start hunting for ignition problems.
Don't unplug anything while the engine is running. That includes the spark plug cap. These systems can produce a lot of volts, like 18,000-30,000 and more. It's got to go somewhere. Readers Digest magazine had a big expose' on bad auto mechanics. They pulled one spark plug cap loose and took it to a bunch of different mechanics. They complained that a lot of those mechanics did detailed, expensive tests, instead of just popping the plug cap back on. Those mechanics didn't do anything wrong. Pulling that plug could have fried the entire ignition system. I've seen it happen. When you check for spark, ground that plug to the engine. The spark should easily jump a 1/4" gap. If it won't jump 1/4", or more, outside the engine, it won't jump .030" inside the engine under compression. A handy tool is a spark tester. There are lots of different types. You can buy one or you can make one yourself real easy. Take a new spark plug and bend the side electrode out straight. Now solder a small clamp on the side and you are done. Clamp it to the cylinder head and hook up the spark plug cap. Crank the engine and you can easily see the spark. The engine can and will run if you connect the tester clamp to the end of the spark plug. Provided, of course, the plug is good and installed in the engine.
Remember, that spark is what sets the air/fuel mix burning. It can do the same outside the engine too.
Make sure there is no spilt gasoline or other flammable mixtures on or near that Spark Tester.
Keep a fire extinguisher handy !

motorcycle work

Well, if you are one of those wicked people who don't bother to maintain your points ignitioned bike you will find the spark of your fire does indeed go out. So what do we do to prevent this ?
Points Ignition is on it's way out, but there are still a lot of them out there. Most engines (but not all) made after 1980 have an electronic ignition and no points. Most engines (but not all) made before 1980 have points. To find out look under the points cover. this cover will usually have two or three screws holding it on. On most single and twin cylinder engines it is usually on the cylinder head, right or left side. On most four cylinder engines it is usually on the crank end and again it can be on either the right or left side but it seems mostly on the right. Three cylinder engines seem to be mostly on the left.
If there is any doubt as to the condition of the points, replace them. Sometimes a good looking set of points can cause a funny misfire that can only be cured by a new set. If the points are pitted badly you will not be able to get an accurate gap setting. Replace them. I have spent way too many hours trying to make a used set of points work, in vain hope of saving $10-$15. Save your time and nerves, buy a new set of points. Interestingly enough, it's been my experience that condensers almost never wear out. I have found maybe four or five bad condensers in the last 35 years. Everybody pushes you to buy them, but I never replace them unless they test bad. They make little cheap testers (at least they used too !) that work quite good. A rough and ready way to test them is to connect the pig tail to the positive terminal of a 12 volt battery and the body to the negative terminal. This charges them up. Now ground the pig tail to the body and, if it is good, you should see a nice fat spark. In some cases the condenser will have two leads. One goes to ground and one to the points hot wire. Connect them by the color coding of the wires. If both wires have the same color, they can be connected either way. Same way to test. One wire to positive and one wire to negative to charge and then touch them together. You should get a nice spark if they are good. The condenser keeps the points from arcing when they open. The condenser can be anywhere in the line (wire) going to the points. Sometimes this is quite a ways away from the points. Like under the gas tank. The capacity of a condenser is measured in microfarads (0.2 microfarads being the average capacity) and that capacity is matched to the points. If there is a big build up of material on one of the points it means the capacity of that condenser is too big or too small for that set of points. If the negative point (grounded or stationary point) loses material, with the build-up on the positive ( Moveable ) point. The condenser capacity is too low. If the build up is on the grounded point ( Stationary ) the capacity is too high. While you are replacing the points go ahead and take the points plate off and check out the It is usually attached to the point cam. Make sure it is working smoothly.
Ok, we got a new set of points and we found where they go... now what ? When you connect the points wire to the points it must go to the movable point and that point is insulated from the stationary point. The little screw that holds the point wire must be insulated from grounded, stationary point. There are usually several little fiber washers and a fiber tube that keep the point spring and screw from grounding. Turn the engine over until the highest spot on the points cam aligns with the points heel. This is the spot where the points are at their maximum opening. Now use a feeler gauge, of the right thickness, and set the point gap. After you tighten the point screws, recheck the gap. Most times it changes a little and it may take several tries to get it right. Point gap can be as little as .010" or as much as .022". Look in your shop manual. Most Japanese bike have a gap of .012" to .016", so use .014" and you will be about right... at least for Japanese bikes.
Now take a circuit tester light and ground one end to the engine and the other to the hot wire going to the points. Sometimes, it's easier to connect to the points spring. Turn on the ignition and turn the engine backwards with a wrench on the crankshaft nut or bolt. If the points are on the left side of the engine this would be clockwise. If the points are on the right side of the engine it would be counter-clockwise. Keep turning until the points close. Keep going till the flywheel mark, usually an "F", has moved well beyond the stationary mark on the crankcase. You go well beyond the crankcase mark so any play in the spark advance will be taken up when you turn the engine forward. Some European bikes use "O", Harleys use a vertical line for the front cylinder and a "O" for the rear, and sometimes a "O" and a "OO". Like always, check the manual.
Now turn the engine in the direction of rotation slowly until the. The light in the circuit tester should come on just as the two marks line up. If they don't, loosen the screws that hold the points carrier plate to the engine and turn it one way or the other till the marks line up. Tighten the screws and recheck. If the engine is fresh and strong, time it so the light comes on exactly when the marks match. If the engine is worn, you will want to advance the timing (See the Ignition timing page.). More wear, less compression, more advance. If in doubt, just use the stock timing marks. When you tighten the points and points plate screws, the points and plate will usually change just a little. Sometimes they change a lot. Recheck the timing after you tighten everything up. If the timing was right on and then advances when you tighten the screws, loosen the screws and set it a bit retarded. When you tighten the screws, it will advance a bit and be dead on. Do the opposite if the timing retards when you tighten the screws. You will also notice two marks on the flywheel that are before (Advanced from) the "F" mark. These marks are the full advance marks. If you shine a timing light at them with the engine running four or five thousand RPM you will see that they are supposed to line up with the stationary mark. You will also see lots of oil flying everywhere if the flywheel is the "wet" type like the Honda Trail 90s, 160s, 175s, 350s, 450s and others. Unless you want to make a special cover with a window in it, you don't really need to use a timing light. Bikes of this type seem to time just fine in the retarded spark position. If the bike is one of the Honda fours, the Yamaha 650 twin and others, you don't have to worry. You can use the timing light.
Some bikes have a timing hole. This hole is covered with a plug. You remove the plug and replace it with a special clear timing plug. This keeps the oil in the engine and off you. Examples of this would be Honda Gold Wings and all Harley Davidsons. The plugs don't seem to work all that well unless you screw the plug in so it almost touches the flywheel. Then it works real good ! You can do this with the Harleys pretty easy, just screw it in a bit more. Others are harder, but you get the idea.
These points plates all have elongated holes in them allowing you to adjust the plate. Sometimes if you need more adjustment, you can take a small rat tailed file and file more length to the elongated hole.
Point gap is not supposed to be used for the adjustment of timing, but sometimes we can use it for that. Wear, on the different mechanical ignition parts, may require us to use it to adjust timing. Other times the manufacturer designs it that way, even though that is not a good thing to do ! The gap of the points is supposed to control how long the Ignition Coil(s) is charged by the battery. The time the points are closed is called the Dwell Angle. This angle is given in the shop manual. This can get complicated because some systems charge the coils when the points are open and others when they are closed. We won't worry about that and anyway most of the points we will be dealing with charge when the points are closed and fire the spark plug when the points open. Just be aware that you can vary timing a little with the point gap, but you want to stay within the maximum and minimum specs so the coil will charge right.
Some twin cylinder bikes, like the old 350cc Honda twins, have both points screwed to the points plate. On these bikes you must use the point gap to adjust at least on of the cylinders. Usually, you can set the gap on one point set, turn the point plate to set the timing and then use the point gap to adjust the timing on the second set of points. Now check the gap on the second set and if it is within spec you are done. If not, you will need to juggle settings on the other set of points and points plate to get everything within spec. To help things out, some manufacturers use an extra plate that holds one set of points and bolts to the main points plate. It is moveable, so you can keep the gap right and still adjust the timing for that point after you have adjusted the other set with the main points plate. Most four cylinder bikes that use points have this extra plate. Some twins use them too.
Points tend to blacken with corrosion when left sitting for a long period of time. You can clean them with a points file. I don't use the metal ones that look like small files. I never could get them to work right, the metal used in points is just too hard to file good. It's also not a real good idea to file points if they are badly pitted because it cuts down on their contact area. If you do file badly pitted points you must file ALL the pits away. I use a flexible type that has grinding compound imbedded in it, or a piece of 100 grit sand paper folded back to back. This just cleans up the point surface. If the points are badly pitted, replace them. Now blow everything clean with compressed air and clean with some contact cleaner. Finally, clean the points with a 1/4 inch strip of paper cut from a 3 by 5 inch card and dipped in acetone. Also, put a bit of points grease on the points cam, points heel and the points lubricating felt. If the felt is old and dry, lube it with grease and put one drop of oil on it. If the felt is old and dry, and you only put grease on it, the dry center will pull the grease into the center and away from where you want it... on the points heel. The oil kinda "charges" the dry felt center, preventing this.
The Yamaha XS1100 is the only bike engine I know of that has a vacuum spark advance. Why have vacuum advance ? Under part throttle, air intake into the intake manifold is restricted, so a vacuum develops in the manifold. Because of this vacuum less air/fuel mixture is drawn into the cylinder. This, in effect, lowers the engines compression and slows the burn rate of the fuel mix. To get the full power out of the engine under these conditions requires more Ignition advance. The Vacuum advance gives you this advance when there is vacuum in the intake manifold. Most car engines have a vacuum advance, but it just didn't catch on for motorcycles.
If you reverse the low tension ignition coil connections it will reverse the polarity. It takes 40 % or so more voltage to fire the spark plugs on a ignition system with positive polarity. On most bikes you would have to really work at it to do this. However, some four cylinder bikes like the early Honda fours are designed this way with double ended ignition coils. One lead is positive and one lead is negative. This means two of the plugs will require a lot more voltage to fire than the other two. Not much you can do about it, but if two plugs start fouling out on these bikes, this might be the reason. To test polarity put a pencil lead between the high tension lead and the spark plug. If there is a flare from the pencil to the spark plug, the polarity is correct. If the flare is between the lead wire and the pencil the polarity is wrong.
I've found that a set of points seems to go out of time in about 2000 miles. If you are willing to live with lousy performance, they can go upwards of 8000 miles.
With the ignition on, you should have battery voltage going to the points. With the ignition on, if you take a screw driver and ground out the the moveable point, when you remove the screw diver from the ground, you should get a spark at the spark plug. With the ignition on and the points closed, open the points with a small screw driver. This, also should produce a spark at the spark plug. The spark should easily jump an air gap of 1/4" or more, to ground, outside the engine.