Service

SERVICE

The incredible badness of baldness

Paul Dean

My riding buddies continually hassle me about the nearly bald front tire on my Honda 1200 Gold Wing, but I tell them that it's not a problem. In fact, it actually has better traction than their deeply treaded tires. Look at the racers on their "slicks" with no tread at all. Wet-weather performance is also not a problem since, due to their round cross-section, motorcycle tires don't hydro-plane. And as far as rubber goes, there is about a quarter-inch of rubber remaining below the tread, above the cords. Please tell these guys that I'm doing the right thing (and saving money) by riding on it until I see cords.

rds. Bert Sisson Baldwin. Michiaan

Unless this letter is a prank, you are an accident desperately searching for a place to happen. There is so much wrong with your line of thinking that I won’t even try to explain it all in such a limited space.

First of all, motorcycle tires do hydroplane, and when they do it, the experience is far scarier than it is in a car. The tire companies don’t put those deep grooves in the tread to be artistically expressive, as though they were decorating a birthday cake; the specific purpose of the grooves is to channel water out from under the tire to reduce the likelihood of hydroplaning. Have you ever seen what happens on a roadrace track when it suddenly starts raining? In any areas of the track where water accumulates, the bikes skate around on their smooth slicks (hydroplane, in other words) almost as though they were on ice. The riders immediately make a pit stop for a quick switch to rain tires, which have even more tread blocks than conventional street tires.

Then there’s your philosophy about the amount of remaining rubber between the base of the tread grooves and the cords. That quarter-inch (or less, on many tires) is there to provide a margin of safety and help maintain the structural integrity of the carcass. When you use that rubber as a tread surface, you run the severe risk of the tire being punctured by any number of normal road hazards-not just a nail, but a little stone, a small scrap of metal or just about anything with a sharp edge. And the less rubber there is above the carcass, the faster that air can rush out of the tire.

So, if you get a puncture when you ’re just about down to the cords, the tire can go flat before you have a chance to slow down and get off the road safely.

Apparently, you are one of a small number of motorcycle riders who think of tires simply as rubber rings that keep the rims off the ground. But tires are much more than that. In one way or another, everything a motorcycle does is an interaction between it and the road, and it only touches the road in two very small patches. Logic then dictates that the nature of those two patches is critically important to the bike’s behavior. To believe otherwise is to disregard your own safety—as well as that of anyone who might accompany you on the back of your Gold Wing.

Double clutching

I'm confused about the clutch adjustment procedure on my `03 Harley-Davidson Road King. On a recent ride with my wife on the back, the clutch began slipping a little bit, mostly when I would use full throttle in high gear. The lever didn't have much freeplay in it, so after I got home, I gave it about a quarter-inch of slack with the adjuster in the middle of the cable, but the clutch still slips. My riding buddy says I need to adjust the screw on the pressure plate, but I don't see why, since the lever already has plenty of freeplay. Does this mean I need to replace the clutch?

Danny Ackerman Oklahoma City, Oklahoma

I have no way of knowing f your clutch should be replaced, but as far as its adjustment is concerned, your friend may be correct. Think of the clutch actuation system on your bike as being divided into two segments: In one segment, the clutch cable connects to a ball-and-ramp mecha nism-sometimes referred to as a clutch l~fler-situated at the right end of the mainshaft, inside the right-hand transmission cover; in the other segment, a pushrod runs through the hollow transmission mainshaft, between the l~fler and the pressure-plate adjustment screw on the left side of the transmission. When you squeeze the clutch levei~ ______

the cable rotates the l~flei' which pushes the pushrod slightly to the left. The move ment of the pushrod against the adjustment screw l~fis the pressure plate, releasing the spring pressure on the clutch plates and disengaging the clutch. When the clutch is correctly adjusted, there must befreeplay between the pressure plate, the pushrod and the l~fler; if there isn `t, the pressure plate won `t be able to exert full force on the clutch pack and the clutch will slip. As the fiber clutch plates wear, the pressure plate gradually moves to the right, reducing the freeplay and possibly eliminating it altogether~ To a certain extent, the proper freeplay can be recov ered by simply turning the mid-cable adjuster.;

But the lifter has a limited amount of rotation and side-to-side movement; so, if you adjust the clutch using only the cable adjuster and the clutch plates have worn significantly, it’s possible to give the lever the required amount of slack, but there may still be no freeplay between the pressure plate, pushrod and lifter. Consequently, the clutch will slip.

To properly adjust the clutch, you first turn the mid-cable adjuster all the way in, giving the lever as much slack as possible. Next, loosen the locknut on the pressure plate and back off the nut and its adjuster screw several turns. Then, while holding the locknut in place with a wrench, turn the adjuster screw inward (clockwise) until you feel resistance against the pushrod. From that point, back the screw out between half and one turn, then tighten the locknut. Finally, use the mid-cable adjuster to give the clutch lever the required Vi&to Vs-inch of freeplay. If you follow this procedure and your clutch still slips, the plates will need to be replaced.

Duel of the dudes

In your "Free torque trick" response in the August Service column, you state that an engine might be able to make a little extra torque if the valve clearance is set at the loose end of the adjustment range, but then you claim that, “You have to adjust the valves more frequently.” Dude, what were you thinking? The valves are loose already, so adjustment will be needed less frequently, unless you insist on keeping them at their loosest setting. In that case, adjustments should still be needed only at the regular interval, not more often as you indicate. Set ’em straight! BMWriderOOl Posted on America Online

Dude, ever hear an engine with a valve tick? Dm sure you have, and Fve encountered more than I could possibly count. That ticking wasn’t caused by a valve that was too tight; it was the result of a valve that was too loose, and it got that way through normal running.

Granted, valve clearances usually tighten up as the valves and their mating seats get hammered from the constant impact of closing. But not always. Other factors can cause the clearance to increase, the most common being wear of the cam lobes, cam followers and valve stems. If you start out at the loosest end of the allowable clearance range, the opening impacts between those components often tend to be more forceful, accelerating wear. In my August response, I probably should have said that,

“ You may have to adjust the valves more frequently, ” but I still stand by the rest of my statement.

Liquid horsepower

I have an ’83 HondaNighthawkCB650SC. Can I continue to add off-the-shelf octane boosters to my gas to improve performance without hurting my engine? For each full tank, I pour in about 4-5 ounces of 104+ Boost or other various octane additives that make my Nighthawk have the extra power that I like. The bike only has 13,000 miles on it, and I do all the regular maintenance and oil changes on time.

Jeff Diggs Holland, Pennsylvania

I hate to burst your bubble, Jeff, but octane booster does not, in and of itself, give an engine any more power; it merely provides gasoline with a greater ability’ to resist abnormal combustion. In some engines—such as those designedfor all-out racing or with very high compression ratios, or engines with large bores that have less-than-optimnm combustion-chamber designs-the mixture can be ignited by sources other than the intended spark. These sources can be hot spots in the combustion chamber, or the fuel can ignite merely as the result of being compressed.

This is called "pre-ignition, "and it not only causes a loss of power~ it can wreak havoc on engine internals. Increasing the octane of the fuel raises the point at which pre-ignition occurs by controlling the combustion more effectively But it does not increase the energy in the gasoline, and that energy is what the engine con verts to heat and forward motion.

On your Nighthawk 650, abnormal combustion is not a problem. Its compression ratio is only 9.5:1, which is lower than that of most comparable modern streetbikes, and its four-valve combustion chambers are reasonably efficient, even by today’s standards. It didn’t require octane boosters in 1983, and it doesn 't need them today.

Psychologically, you may think the engine is making more power because voit 've put octane boosters in the tank, but it is not. If you run your bike on a dyno and make comparisons with and without octane booster, you will see this for yourself. And over time, you 'll be able to pay for the dyno work with the money you won 't have wasted on octane boosters. □

Got a mechanical or technical problem with your beloved ride? Can’t seem to 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 CW1Dean@aol.com; or 4) log onto www.cycleworld.com, click on the “Letters to the Editor” button and enter your question. Don’t write a 10-page essay, but if you’re looking for help in solving a problem, do include enough information 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.