Service

SERVICE

Paul Dean

Dirty little secrets

I have always wondered why motorcycles have slower top speeds than cars, even though they’re capable of much faster zero-to-60 or quarter-mile times. No Ferrari or Lamborghini or Porsche can come close to out-accelerating performance bikes like a Hayabusa or a GSX-R1000, yet many of those cars can easily exceed 200 mph. Why is this so? Dave Kerner Posted on www.cycleworld.com

Compared even to the average passenger car, a motorcycle is an aerodynamic disaster. Most modern automobiles have very smooth, contoured surfaces that let them slip through the air rather cleanly, while motorcycles have all kinds of protrusions and irregular, uncovered surfaces that create considerable turbulence and drag. Consequently, bikes without fairings are about as aerodynamically efficient as an open parachute, and even fully faired sportbikes are “dirty” compared to a car. So, even though motorcycles have less frontal area than a car, they have a much higher coefficient of drag. Highperformance motorcycles boast powerto-weight ratios that cars can ’t equal, which explains a bike’s vastly superior acceleration. But the enormous drag that motorcycles bring to the party prevents them from attaining the kinds of top speeds that more streamlined vehicles can reach.

Here ’s a wonderful example: A man I know once bought a used 1985 Honda VF750 Interceptor V-Four engine from a salvage yard and bolted it, unmodified in any way, into a four-wheel streamliner. The car was encapsulated by a teardrop-shaped body, which was a modified wingtip fuel tank from some small jet fighter. An ’85 750 Interceptor had an actual top speed of around 135 mph, but the VF750-powered streamliner reached a top speed of nearly 180 mph, even though the engine was bonestock. Matter of fact, the mechanic who installed the engine in the car never even replaced the sparkplugs. That 45mph difference was the result of aerodynamics and nothing else.

Red-hot Trumpet

I love my ’97 Triumph T595 Daytona except for one problem: It overheats at the drop of a hat! And I’m not talking about letting the bike sit with the engine idling or anything like that. If I have to stop at two or three traffic lights in a row, the temperature gauge goes right into the red. I’ve checked the cooling system pressure, changed the coolant using distilled water, and added Redline’s Waterwetter (which helped a little but not enough). The original thermostat seems okay, but I ordered a new one anyway, and the fan seems to work properly, as well. Is overheating normal for this bike?

Tony Leone Posted on www.cycleworld.com

Those Triumph models do tend to run a little on the hot side, but not to the extent you’ve described. Something definitely has gone awry somewhere in the cooling system. If you have not yet installed the new thermostat, try removing the old one altogether and temporarily run the bike without it. If the temperature then stays within the normal operating range, you ’ll know for certain that the thermostat was the cause of the problem.

Also, those Triumphs are very sensitive to the presence of air in the cooling system; even a small pocket of air can significantly raise the operating temperatures. When filling the cooling system, first remove the small bleeder bolt located right next to the radiator cap. Then add coolant through the filler neck until it starts flowing out of the bleeder hole and is free of any apparent air bubbles. That procedure should eliminate any trapped air in the system.

If neither of these tactics solves the overheating problem, there most likely is some kind of blockage in the cooling system that is preventing the normal flow of coolant. You ’ll have to track it down one step at a time.

Dyno? I don’t need no stinkin’ dyno

I own a 2000 Suzuki TL1000S. I just had a set of Yoshimura race pipes installed and now I want to have the fuel-injection remapped. What is the best way to do this? My mechanic tells me he can remap it on the street, due to his experience, or I can have him do it on a dynamometer. He prefers to do it on the street, claiming that all the dyno tells him is the engine’s horsepower and torque. And should I change the air filter? Some people say that doing this sometimes does more harm than good. Jeff Whipkey

Posted on www.cycleworld.com

I assume the mechanic in question remaps the injection system by using one of the more commonly available devices designed to accomplish that task. Some shops and tuners use a fuel-injection adjusting tool made by Yoshimura that allows the fuel curve on injected Suzuki models to be recalibrated. And Dynojet and K&N both sell the Power Commander, which is a programmable, plugin supplement to the Engine Control Module on fuel-injected motorcycles.

If your mechanic knows what he is doing and is familiar with the TL’s idiosyncrasies, he probably can adequately remap your injection system by riding the bike up and down a local street at various rpm and throttle settings. Personally, I prefer to do this type of tuning first on a dynamometer, which allows me to accurately quantify the results of any adjustments I make, then verify the eventual outcome by road testing the bike. But I’m amused by the mechanic s statement that “all the dyno tells him is the engine’s horsepower and torque.’’ Uh, what else is there? Or has he discovered that internalcombustion engines produce some other kind of propulsive force that the rest of us don’t know about?

As far as the air filter is concerned, installing a freer-flowing filter element will not harm a thing. Yoshimura, in fact, recommends the use of its BMC oiled-gauze filters in conjunction with the installation of one of its exhaust systems and the remapping of the fuel-injection.

Meat lover’s F3

I have a ’95 Honda CBR600F3 fitted with a 160/60-17 rear tire, the same size as the original. I would like to go up to a 170/6017 tire to give the rear a meatier look, but I’ve been told that a bigger tire will balloon up in the center and make the bike illhandling. Is this true? If so, can I increase the rear rim size to solve the problem. What is the widest rim I could use? S. Ward Posted on www.cycleworld.com

Don’t worry about increasing rim width; your F3 can handle a 170/60 tire with no adverse effects on its handling. Most 170series sport tires are suitable for mounting on rims from 4.5 to 5.5 inches in width,

and your Honda ’s rear rim is 5 inches wide. But if you go any wider-to, say, a 180/55-17, which is the next size larger-the rim will be too narrow and the tire will lose its intended tread profile; that size tire requires a 5.5or 6-inch-wide rim. Besides, beyond a 170 tire, chain clearance on your F3 becomes a problem that has no easy fix.

A Suzuki in drag

I own a 2000 Suzuki 1500 LC, and I’ve installed 2-inch drag pipes and rejetted the carbs. The bottom-end performance is good, but the top-end acceleration is a problem. It tops out at only 90 mph, and from about 65 mph, it’s slow in reaching that maximum speed. The pipes are open with no baffles in them. I’m anxious to see what you have to say. GllSS Perry Posted on www.cycleworld.com

The culprit here is the exhaust system, pure and simple. Drag pipes were initially conceived years ago for drag racing, a sport in which an engine only uses a narrow band of rpm at the very top of its rev range. Tuners found that they could maximize peak power with straight, simple exhaust pipes cut to the ideal length for that particular engine ’s peak rpm range. The pipes were only effective in that one specific rpm spread, though, so they didn’t work very well at any other engine speed. But for drag-racing purposes, that was a perfectly acceptable compromise.

Over the years, drag pipes have become very popular, especially for V-Twin streetbikes, but the same compromise still exists. Unlike other types of exhaust systems that utilize numerous internal design elements that help produce a broad powerband, drag pipes can’t be tuned to work over a wide spread of rpm. So while they often yield a decent power increase in one particular rpm range, they invariably produce flat spots elsewhere.

You didn’t mention what brand of pipes your bike uses, but they apparently are not tuned for higher-rpm power on a 1500 LC Suzuki. Your only options are to live with the compromises those pipes bring about or replace them with something else better suited to your needs.

Tick, tick, tick...

I have a 2000 Yamaha YZF-R1 that only has 450 miles on it. When the engine is idling or when I give it just a little bit of gas (between idle and, say, 3000 rpm), I hear a ticking sound coming from the top part of the engine. My dealer says that one of the valves is loose and needs to be adjusted, but a friend of mine, who also is a mechanic, says I should leave the valves alone for the present. Fie says that I should finish breaking-in the engine and that when the break-in is complete, the ticking will probably stop. Who is correct? And what is causing the ticking? Is it a loose valve hitting the piston? Your help would be greatly appreciated. M.G. Buttigieg Posted on America Online

Your friend could be right: That ticking just might go away by the time the breakin period is complete. But he’s more likely to be wrong; seldom have I seen a noisy valve quiet down as the miles accumulated. The ticking is not caused by the valve hitting the piston, b t instead is the result of excessive clei ranee between that valve’s cam lobe and its mating bucket-type tappet.

There are all kinds of different components and materials involved in the cylinder head and the valve gear, and each component is subjected to different levels of heat. Consequently, there are numerous different rates of expansion among those components as they make the transition from cold to normal operating temperatures. So, there needs to be a specific amount of clearance between the lobe and the tappet to compensate for those variations in expansion. What’s more, most camshafts are designed with what are called quieting ramps, which make valve operation less noisy. The ramps do this by gradually taking up the clearance before the lobes begin pushing the valves open, and by allowing the valve to close more slowly rather than slamming shut.

If the valve clearance is too small, the cam lobes will prevent the valves from fully closing once the engine heats up, even on the lobes ’ lowest points. And if the clearance is too large, the quieting ramps are rendered useless, causing the ticking sound you hear. If the ticking is allowed to continue unabated, damage to the valve can occur.

My recommendation is obvious, then: Get the valves adjusted now. Even if your 2000 R1 is out of warranty, a valve adjustment now is much cheaper than a valve job later.

How to battle the rattle

In your June Service column, you replied to a reader who complained of an exhaust rattle (“‘RR’ means rattle, rattle”) on his 2000 Honda CBR929RR. Your reply was based on your consultation with our service department, but I want to offer some more accurate information on the subject. We have, in fact, published this information in a technical newsletter, called The Wrench, that we send to our dealers: “If a CBR929RR owner comes in asking about cam-chain noise or some other type of ‘engine rattle,’ try listening to the EGCV (Exhaust Gas Control Valve). The EGCV bushings are made of carbon and will wear with normal use. Use a sounding rod or stethoscope to verify if the sound is caused by worn bushings. The complete bushing replacement procedure is detailed in the CBR929RR Service Manual on pages 5-102 and 5-103.”

Though the information we previously provided you indicated that this rattling is normal and cannot be remedied, bushing replacement will in fact go a long way toward quieting the noise. I’m sorry that we didn’t have this information to give you when you wrote your response.

Pete terHorst American Honda Motor Co. Torrance, California

Thank you for the follow-up. I’m certain that the riders of those rattling 929RRs appreciate the additional information. □

Got a mechanical or technical problem with your beloved ride? Can’t seem to find reasonable solutions in your area? Maybe we can help. If you think we can, either: 1) Mail your 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 CW1Dean@aol.com; or 4) log onto www.cycleworld.com and click on the Feedback button. Always include your name, along with your city and state of residence. Don’t write a 10-page essay, but do include enough information about the problem to permit a reasonable diagnosis. And please understand that due to the huge volume of inquiries we receive, we can’t guarantee a reply to every question.