Service
SERVICE
PAUL DEAN
Scoping it out
Q I recently changed the exhaust system on my 1986 Yamaha SRX:6, and it sounds to me like there now is an exhaust leak. It's been hard to diagnose the problem because within a few seconds after the engine is started, the exhaust system becomes too hot for me to check for leaks using my fingers. Is there a way to find an exhaust leak that doesn't involve burnt flesh?
John Kara Napa, California
A I've always had great success in tracking down exhaust leaksand many other engine noises-using a stethoscope designed for such tasks. In the April, 2009, Service department, I featured a nice stethoscope from Graham Tool Co. (www.grahamtool.com; part #52750, $32.95), and you can find a variety of others at most auto-parts outlets, through online sources and even in the tool depart ments of many retail giants like Home Depot, Lowe's and Sears.
Essentially, the stethoscopes involve
two hollow metal tubes that fit into the wearer's ears and are joined together at the bottom where they plug into a long piece of flexible rubber or neoprene tubing that, in turn, connects to a round amplification chamber. Inside the chamber is a thin metal diaphragm attached to the top of a long metal rod that is used as a probe.
To find the source of mechanical sounds, you place the end of the rod against various hard components in the suspected area. The rod acts as a conductor that transmits sounds up to the diaphragm, which then amplifies them and passes them up through the hollow tubes, into the wearer's ears. You just keep moving the rod around until you find the location where the sound is the loudest, and that is usually the source.
For tracking down non-mechanical noises-including exhaust and vacuum leaks-you remove the metal probe and diaphragm, leaving the chamber open to act kind of like a funnel that amplifies any sounds near the open end. Then, much like with the metal probe, you move the chamber around in the general direction of the suspect ed leak until the noise is the loudest, which invariably will be at the source.
Oil gone AWOL
Q After a recent long ride on my 2002 FZ1 Yamaha (23,000 on the odometer), I changed the oil and filter. Once I drained the oil and swapped filters, I poured in a little more than three quarts of 15W-40, checked the oil level (it looked good) and took off for a short test ride. In less than a mile, the oil light came on. I pulled over immediately, shut the engine down, put the bike on its centerstand and looked at the sight-glass to check the oil leveland couldn't see any! I checked for leaks and there were none. After a few minutes, a little oil showed up in the window, so rather than pushing the beast home, I started it. The oil light came on again just as I got to my driveway.
This is my tenth bike in the last 40-plus years, and I've always done my own maintenance, but I've never had a problem with an oil change. Leaving the bike on its centerstand overnight caused a little oil to dribble into the window, but not enough to give me any joy. I'm assuming that some debris is blocking an oil return passage some where in the lubrication system. Where do I look? Is there an internal filter somewhere? How could anything get in there?
Bob Marsh Prescott, Arizona
A Very strange stuff, Bob, but the evidence-as little of it as there is-points to the oil filter. On your ride just prior to the oil change, everything was hunky-dory, and the only "hard part" difference between then and now that could account for a restriction in oil flow is the filter. You didn't specify the brand of filter you used, and I'm not intimately familiar with the direction in which oil is routed on an FZ1; but if the filter has a manufactur ing defect, such as a faulty anti-drain back valve, it could be preventing full circulation of oil through the system. This would explain why the oil light comes on and no or very little oil shows up in the sight glass.
Truth is, I'm really guessing here as much as anything else, but I suggest you simply spin on another oil filter. That's about the cheapest way I can think of to determine if my diagnosis is correct or I've gotten lost in space.
Rotary club news
Q Why is the simple, smooth, Wankel-type rotary engine not used in motorcycles? On the face of it, this design would seem ideal. Could you please explain why this is not so?
Incidentally, you and Kevin Cameron have taught so many so much, and I, for one, very much appreciate that. Thank you, and please keep it up! Mark Walter
eep it up! Mark Walter Toms River, New Jersey
A Speaking for Kevin and myself, you are very welcome, Mark. We strongly believe that information is a precious commodity meant to be shared, not hoarded. It's fundamentally the same mentality that motivates some people to become teachers.
In response to your question, there have been several motorcycles over the years to use rotary engines, the most ambitious being the Suzuki RE-5 sold between 1974 and 1976. DKW also built a smaller, more simplistic rotary bike, and Norton has maintained an on-again! off-again love affair with rotary-powered racing machines.
Rotary engines indeed are simple and smooth, with fewer moving parts than in the reciprocating variety, plus they are generally lighter and more compact. But they are not without their problems, one of which is excessive heat. In a reciprocating engine, heat is generated in one place, the combustion chamber, which gets cooled between each burn with a fresh shot of incoming fuel mixture. The combustion chamber in a rotary, how ever, is not stationary; as it pushes the rotor through its path, the chamber "moves" along nearly half of the engine's internal surfaces between sparkplug and exhaust port, and those surfaces are never cooled with incom ing fuel mixture. As a consequence, a rotary runs hotter and radiates more heat than a piston engine; and since lost heat is lost energy, the rotary gets poorer fuel mileage.
Rotaries also do not make as much lower-rpm torque as piston engines are ca pable of producing, but they can be tuned to make higher horsepower numbers with less displacement (although displacement comparisons between the two engine types are a constant source of argument). In addition, the seals on the tips of the rotor have been prob lematic since the design's very inception, frequently resulting in rapid seal wear, leakage (causing increased oil consumption and power loss) and even outright fail ure. And last but certainly not least, getting a rotary to comply with emissions regulations is far more difficult than it is with piston engines.
If rotaries had undergone the same 125 years of continuous, worldwide refinement as have piston engines, maybe they would be superior in every way. But they haven't, and so they are not. They are perfectly viable engines, as Mazda has proven for decades, but they're not The Answer for motorcycles.
M/C hammer
Q My 2007 Honda VTX1300 started making a hammering nois~at 700 miles that sounds like it's in the front, lower part of the engine, like maybe it's a main bearing. The bike now has 9000 miles on it, and the noise seems to have gotten a little worse but not much. I hear it most at around 11 mph in first gear. It makes the noise in all gears, but at that certain speed and rpm, it seems to be the worst. The dealers are willing to tear the engine down, but if they can't find a problem, the warranty won't cover it and I'll have to pay for repairs. Is this a problem that you are familiar with, and if so,do you have any suggestions?
Burhi Nietiedt Cabot, Arkansas
A As I've stated several times in the past, it's nearly impossible for me to diagnose the cause of a noise with any degree of accuracy when I can't actually hear the noise. Having said that, however, I suspect that what you are hearing is the effect of normal side play between the VTX's crankshaft and the engine cases.
All engines need to have a small amount of side-to-side clearance between the crankshaft and the main bearings to allow for expansion caused by heat. Manufacturing tolerances allow for a small range of variation in this dimension-as well as most others-so some engines end up with more crank sideplay than others. The loads placed on the crank, however, are asymmetri cal; in your VTX, for example, the crank drives the entire motorcycle via the primary gears on the right, but it only has to spin the alternator flywheel on the left. That alone keeps the crank constantly shifting back-and-forth in its freeplay as it rotates. What's more, the two connecting rods in your V-Twin are side-by-side on the same throw, so the forces acting on them create a rocking motion that tends to alternately thrust the crank to one side of its freeplay and then to the other. Then there's the uneven firing sequence of a V-Twin, which exacerbates many lower-rpm engine noises because of the constant rpm variations it causes. When the engine was new, the noise was not soapparent; but as it broke in, the involved components loosened up, causing the noise to be much more audible.
FeedbackLoop
Q I used to ride SoCal motocross and desert in the `60s and `70s, and I had aleft-hand numbness problem like the one described by Brian Fletcher ("Looking for a buzzkill," June issue). I wondered why it always was my left hand and never the right, so I converted a throttle twistgrip tube to the left side by potting the cable drum with silicone, and most of the problem went away. I think the little annular space between the bar and the throttle tube allowed the vibration to dissipate. I then plugged both ends of the handlebar with pipe plugs, drilled and tapped the bar between the clamps and filled the inner space of the bar with silicone oil pres surized to 150 psi. It sure helped.
When I purchased my SV650 Suzuki in 2000, I had the same problem and found that Boyesen Engineering (wwwboyesen.com) makes a throttle-type left-hand grip that re duces vibration. It uses two plastic "worms" that hold the throttle drum from rotating but still allow a small amount of movement to absorb vibration. It comes with worms of varying density for tuning purposes. Maybe Mr. Fletcher should try it. Brian Fabre
lul Lullilly pUI~JU~~ vIdyu~ )uld try it. Brian Fabre Posted on America Online
Q Thank you for the great suggestion. I'm sure that the "other" Brian will be especially appreciative.
So, while it is entirely possible that your VTX1 300 does have a serious engine problem, I believe that the noise you describe is normal-and in the end, harmless.
Got a mechanical or technical problem and can't find workable 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@ aoLcom; or 4) log onto www.cycleworld. corn, click on the "Contact Us" button, select "CW Service" and enter your question. Don't write a 10-page essay, but if you're looking for help in solving a problem, do provide enough information to permit a reasonable diagnosis. Include your name if you submit the question electronically. And please under stand that due to the enormous volume of inquiries we receive, we cannot guarantee a reply to every question.
