Service
SERVICE
PAUL DEAN
A V-Twin musical
Q A few months ago, I purchased an exceptionally nice 2005 Harley-Davidson 1200 Sportster that only had 2300 miles on it. I really like the bike and am happy with it, but the one thing I want to change is the exhaust sound. My favorite bikes for sound are Ducatis, and because they are V-Twins like my Sportster, I’ve tried to get the same sound by using three different exhausts, but I haven’t had any success. The bike still sounds like a Harley. That’s not bad, but it isn’t what I want. Is there something else I can do, like changing the cams or some special exhaust I don’t know about, that could give my bike the sound I’m after? This is really important to me, but everyone else I ask just laughs and says it’s impossible. David Bradford Huntsville, Alabama
A I promise not to laugh, but I will tell you that what you hope to accomplish indeed is impossible. A Ducati V-Twin engine is not “like” your Sportster’s V-Twin engine in one very important aspect: its Vee-spread. The Ducati is a 90-degree Vee and the Sportster is a 45-degree Vee, and where sound is concerned, that makes for a considerable difference. And not just with V-Twin engines; the number of cylinders, their orientation to one another and their firing sequence all have a dramatic effect on how an engine sounds, even though the very same combustion events might take place in every one of them.
These differences are caused by the ways in which sound waves interact. When sounds have multiple sources that occur in rapid succession rather than all at once—such as in engines of more than one cylinder—some of the sound waves complement each other, some compete with one another, and the timing between each wave is important in dictating the sound that ultimately results. It’s a fascinating phenomenon that some people liken to the variations in sound produced by different wind musical instruments.
Then there’s the matter of rpm range. Your Sportster’s engine is redlined at 5500 rpm, if memory serves, while a typical Ducati’s rpm limit is up in the 9000-to-l 1,000 range, depending upon the model. That factor alone will produce an exhaust note that your Harley could not equal.
So, if you want a bike that sounds like a Ducati, you will have to buy a Ducati or one of the other motorcycles powered by a high-performance, 90-degree VTwin engine—such as a Suzuki SVI000, Honda RC51 or VTR1000 Super Hawk. Aprilia’s 60-degree V-Twins come close in sound, but because of that 30-degree difference in Vee spread, even they produce a slightly different resonant tone.
Where, oh wear
Q I have a question about your July-issue analysis of the #4 cylinder problem on Michael Robbins' 1975 Honda CB400F Super Sport. We who are old enough to remember what gems those 350s and 400s were also recall that they had to be on the boil to achieve the desired performance. But at a mere 12,000 miles, can a cam lobe or rocker shaft on a 400 wear that much +unless the bike had been really abused?
Bill Malandra Durango, Colorado
A Absolutely. I saw several such component failures on those models back then, and not all were the result of what could be termed "abuse." Sometimes, a cam lobe or rocker had escaped the factory without sufficient surface hardness. On a couple of oc casions, the problem occurred due to a low oil level caused by a small, unde tected oil leak. Other times, it was the result of the owner not changing the oil and filter often enough or just chang ing the oil but not the filter. I guess you could call some of those factors abuse, although back in the early 1970s, most motorcycles were more susceptible to even slight tardiness in performing scheduled maintenance than are today's bikes. But even the most sophisticated of current motorcycles still have war ranty issues, proof that they remain imperfect machines manufactured by imperfect human beings.
Pop! goes the Guzzi
Q For more than a few years now, my ’77 Moto Guzzi 850 T-3 has been doing something strange. After it sits for a day or more and I turn on the ignition switch to find neutral before starting, the right cylinder will fire. It does this almost every time before I push the Start button, and it often does it when 1 turn the ignition off. It never happens when the engine is hot and never on the left bank. The engine has NGK plug wires, Dyna III electronic ignition, Flame Thrower epoxy-filled coils and T3 sparkplugs. It starts easily, idles fine and runs great. 1 recently rebuilt the carbs, including new float needles. The valves are right, as is the timing, but nothing I’ve ever done has stopped this problem.
Also, when the ignition switch is turned on, the voltage at each plug will spike to 7 to 10 volts (just for an instant). My ’04 Honda does not do this; its voltage remains at zero. Any ideas?
Tom Morgan Sylvania, Georgia
A For a cylinder to make fire, two ingredients must be present: fuel and spark. You've already answered half the question by determining that the plugs get a shot of current when the ignition is turned on. Evidently, that current is enough to deliver a spark. Fundamentally, ignition systems produce a spark by passing a magnetic field through a coil consisting of thousands of winds of fine wire. I am unfamiliar with the characteristics of your Dyna III ignition, but turning it on apparently creates and expands a magnetic field, producing a spark; turning the ignition off collapses the field, also producing a spark.
I admit to guessing here, but I have to believe that the right carb on your Guzzi still has a very, very slow leak that allows tiny amounts of fuel to seep into the cylinder, even though you have rebuilt the carbs. Perhaps the seat that the new float needle mates with has an imperfection, or maybe the leak is between the seat and the body of the carb. Whatever the leak’s cause, its rate is insufficient to allow any meaningful amount of fuel to accumulate in the cylinder in an hour or so; but overnight or even longer, enough gasoline can dribble into the engine and—most importantly—continually atomize into an easily ignitable vapor that combusts when the ignition is turned on or off, creating the Pop! you hear.
There’s an easy way to be certain that the problem is with the right-side carburetor: Swap it with the left one.
If the condition then moves to the left cylinder—which I am almost certain it will—you’ll need to either go through that carb once again or try to round up a replacement.
Of course, since the popping seems to be harmless, as evidenced by its continuance for, as you put it, “more than a few years,” you could do nothing. That’s not what I suggest, but it is an easy option.
Getting a "feel" for it
I just bought a 1968 Triumph Bonneville from an older gentleman who has been unable to ride it for the last dozen years. I’ve cleaned it up to the point where it looks nice, and it runs good, too, except that the valves are noisy. I would like to adjust them myself, but I’ve never done it before. How do I know if I am measuring the clearance at the right place? I know that cam lobes are eccentric, but I don’t know how to tell when a lobe is at the right place for adjustment. And how snug should a feeler gauge be when 1 slide it between the rocker arm and the valve? I’ve been told that it should be hard to push and also that it should go through with no resistance. Can you set me straight?
Carl Richter Des Moines, Iowa
A Sure can. Your Triumph has a 360-degree crankshaft, which means that whatever one cylinder is do ing at any given moment, what the other is doing is exactly the 360-degree oppo site. That makes positioning cam lobes for valve adjustment a piece of cake. You want to make adjustments when the tappet is on the "heel" of the lobe, directly opposite the point of greatest lift. So if, for example, you want to adjust the left-side intake valve, simply turn the engine until the right-side intake valve is at its fully open position. That puts the heel of the left intake cam directly opposite from its fully open po sition. Do the same with the other three valves, always positioning its opposite valve in the fully open position. As far as the feeler-gauge issue is concerned, there's a reason those tools got their name: They rely on the user's "feel." But both of your advisors were incorrect. If you have to force the gauge between tappet and valve stem, you are, in effect, partially pushing the valve open and will end up with too little clearance. And if you let the gauge slide through with no resistance, the valve will have too much clearance, and you
Recall Roster
NHTSA Recall No. 1 2V270000 Manufacturer: Ducati North America Model: 20121199 Panigale Number of units involved: 375 Problem: On certain of these models, an incorrect screw was used to attach the swingarm to the rear suspension linkage. If the linkage detaches from the swingarm, catastrophic suspension collapse would occur and adversely affect the rider's ability to safely handle the motorcycle, increasing the risk of a crash. Remedy: Dealers will inspect and replace as necessary, the incorrect screw. Owners not receiving this remedy can contact Ducati at either 800/231 -6696 or www. ducati.com.
won't have any idea how much. Instead, the gauge should push in and out with a smooth, even but slight resistance that will do neither of the aforementioned. This sometimes requires a little prac tice before you get it right. You always should try to make the adjustments as correctly as possible, but fortunately, if you are off by a thousandth or so in either direction, no harm will come to the valvetrain as a result. Some people prefer to make valve ad justments with what are called "go/no go" feeler gauges that have two different thicknesses on each blade, one usually .002-inch thicker than the other. In your case, you would first push the thinner tip that has the desired thickness between valve and rocker, then the thicker part. If the thin part fits but the thick section does not, you know that you are within
approximately .001-inch of your desired setting. But if the thick part of the gauge also goes in easily, you know that the clearance is too great. You can get go/no-go gauges with both American and metric thickness siz ing from Proto Tools (www.stanleyproto. com; part #MT-1022; $18.22) or Lisle Corporation (www.lislecorp.com; part #68150; $19.06).
Got a mechanical or technical problem with your beloved ride? Can't seem to find work able solutions in your area? Or are you eager to learn about a certain aspect of motorcycle design and technology? Maybe we can help. If you think we can, either: 1) Mail a written inquiry, along with your full name, address and phone number, to Cycle World Service, 1499 Monrovia Ave., Newport Beach, CA 92663; 2) fax it to Paul Dean at 949/631 -0651; 3) e-mail it to CWlDean@aol.com; or 4) log onto www.cycleworld.com, click on the "Contact Us" button, select "CW Service" and enter your question. Don't write a 10page essay, but if you're looking for help in solving a problem, do include enough infor mation to permit a reasonable diagnosis. And please understand that due to the enormous volume of inquiries we receive, we cannot guarantee a reply to every question.
