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TECHNICAL WRITEUPS WITH TIPS AND INFO FOR THE VINTAGE MOTORCYCLE ENTHUSIAST

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This month's article was published on August 2010 in the CVMG Newsletter. 

By Ken Mortimer

(Continues from Home Page)

... that I can sneak into this month’s topic before you realize that it is electrical in nature… Still with me? If the top of the page had read “DVOM Basics” or “Making Friends with your Multi-Meter” I’d bet that half of you would have muttered “electrical? eeewww!” and turned the page.

The electrical system is the most misunderstood and perhaps scariest part of the motorcycle for most of us. But luckily there is no need for the average rider to know this system intricately. But having some basic ideas can come in handy. So I promise no formulae to memorize and no plumbing analogies. (remember grade nine shop class? Voltage equals water pressure, the battery is like a water tank, blah, blah, blah. If this is true how come when I attach the hot water pipe to the cold faucet I don’t see smoke?

Within the CVMG stable, dare I say that most of us have bikes that use a 12 volt negative ground system? There are some 6 volt systems out there. And of course there are some positive ground systems alive and well within our ranks. But I’m assuming that most of you riding bikes with these systems are quite familiar with them and probably capable of writing this column. So I’ll concentrate on the common 12v, neg ground and hopefully help some of you who are not so electrically inclined.

To begin with you should own a digital volt ohm meter. (DVOM for short). There is no need to purchase an expensive version. CTC or PA stores often have an adequate DVOM on sale for just $9.99. It’s not the unit I would choose for professional use but it will do everything the casual home user will need.

Which ever meter you select will come with a red wire lead, (for positive) and a black (for negative or ground). Each lead will end with a sharp probe, handy for piercing wire insulation, sliding into a connector or drawing a blood sample from your finger tip. Having at least one alligator clip for attachment at the end of the leads is handy. And a continuity “beeper” is a nice touch.

Your DVOM will have several scales within each of their functions. It’s important that you select the correct scale for the job you are doing. This is not as complicated as you might think. First select the function you wish to work with. For our bikes, this will most often be “D.C. Voltage” or the “Ohms” function. Your meter will usually have an “A.C. Voltage” function, and low “Amperage” capabilities along with many other possibilities.

Next you want to choose a scale that exceeds your expected maximum reading. If checking a voltage reading on your 12 volt electrical system you need to dial in the 20 volt scale. Make sense?

When measuring resistance, (ohms) always start with the highest scale and move down incrementally until you are reading in the zone. (If you want to part with more cash, you can buy an “auto-ranging” meter and the meter will find the correct scale for you. There are reasons that I prefer to stay away from this type of meter but they do make things easier.) Here are a few tests and checks that anyone can make with their DVOM.

Battery condition.- engine off, key off.20 vdc (Volts D.C.) scale, red lead to (+) battery terminal and black to (–) terminal. A fully charged battery will show 13 volts or more, about 2.2V per cell. Less than 12 means you need to charge the battery. Less than 9 and you best go shopping for a new one.

Charging system- same scale and connections as above. But this time start the engine. This one will vary somewhat depending on your motorcycle but you need to see greater than battery voltage when the engine is revving at road speed. So twist the throttle slightly and hope for high 13’s or better on the voltage reading.

Parasitic draw- If you routinely find your bike with a dead battery after a period of non use it could be that something is drawing it down while not running. Disconnect the ground lead at the battery and set your DVOM to the amperage scale. Most inexpensive meters will have a 10amp max capability.

With the key off connect one lead to the battery terminal and the other to the battery lead. You should be seeing zero amps or very close to it. Bikes have very few circuits that can cause you this kind of trouble, (unlike autos) but it can happen. If you own a European brand with an analogue clock you will find a considerable current draw. If you do find that something is “staying on” you then must isolate the circuit causing the problem.

Circuit testing- Back to the 20 volt scale and you are ready to check a faulty circuit. For instance an inoperative brake light. Connect the black lead to the battery negative and look for voltage along the circuit. Remember to apply the brake to activate the circuit. You’ve probably already tried a new bulb so check to see if power is reaching the bulb socket. If so; you’ve got another bad bulb, (or mixed up the old one with the new one and retried the bad one…) OR you could have a bad ground in the circuit. Move your meter black lead to the bulb socket and retest. Work systematically back checking for power at the brake light switch, (both sides) and at any connections. Rarely does a circuit give trouble along a section of wiring unless it has been chafing and worn through. Most problems are at components or connectors.

If you have found a possibly faulty switch you can confirm it’s not working with your meter switched to the Ohm scale or if equipped, the continuity beeper. In these positions your DVOM will tell you if the circuit is “complete” and how much resistance is within that circuit. For the test we are doing we are more concerned with former.

Connect your leads to each side of the brake switch. With no brake application your meter should read infinite on the ohms scale and the beeper should be silent.

Applying the brake should cause the switch to allow power to pass and therefore you should see an ohm reading and/or your beeper should sound.

This method can be carried through to any circuit you wish to test. And any switch can be checked as well. And using the Ohms setting you can check any current consumer: bulbs, fuses, etc. Readings will vary as each part will provide some resistance. But what you are looking for is continuity vs. an open circuit rather than an exact resistance value. Manuals provide specifications for some items such as ignition components. But be wary of condemning these based solely on a resistance test. These parts will have quite specific allowable ranges, most often very low, (thousandths of ohms) and difficult to read accurately.

Electrical issues range from head scratchingly complex, to very simple and armed with a DVOM, some knowledge and some patience you’ll be surprised at what you can solve. Some might even make you smile, like a recent Suzuki on which I had the pleasure of sorting out headlamp troubles…caused by some sort of insects that had nested within the switch housing preventing current flow.

Tech Tips For this month we revisit the gas tank topic. Here are a couple of more submisions that came in after the first article went to print. First up is Trevor who wrote: “I'm currently rebuilding my Chang Jiang 750 and had the tank coated with Scotchkote 134FBE, it's a baked epoxy coating similar to powder-coating so it's not something that can be done at home. I had it done by Corey Harink of Desert Blasting & Painting in Brooks , AB. He's used the coating on his own Chang's with good results. He sandblasted the tank inside and out to remove rust, then sprayed and baked the coating. The only stipulation Corey mentioned is the tank opening needs to be large enough that he can work through it while blasting and spraying the coating. I'm sure Corey can provide more information. His email is casa35@hotmail.com Another option is POR15, they manufacture a kit for treating and coating rusted fuel tanks which is a little more backyard friendly, we just started selling their product so I haven't had any feedback on the tank products yet.”

Next I heard from Ian Sandy. Ian has included a link to his website and it is worth a look, especially if you have an interest in 1970’s Suzuki GT’s. “As per your request for tank sealing info, here are a couple of links to my projects web site - most of the information is still correct, although the Canadian Caswell operation now doesn't seal the same sealant(they now sell the POR-15 product) - I've been quite happy with the result and would buy it again!”

Ian has some detailed tank info as you follow the restoration of his 1976 GT750 Custom. The link to Ian’s bike page is www.sandyfamily.com/oldjapanesebikes

....Ken kmortimer@persona.ca

TECHNICAL WRITEUPS ARCHIVE


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