Service

SERVICE

Paul Dean

The braking point

My 1982 Honda Nighthawk has new brakes-dual discs, master cylinder and steel-braided lines. After the bike sits for a few days, the front brakes lock up, with no freeplay in the brake lever. If I just crack open one of the bleeders, the system is fine. Every once in a while, the lever gets stiff when I’m riding and the brakes begin to drag, and they once even locked up. Bleeding again returns them to normal. Help! Mark Sewak Concord, North Carolina

I responded to this type of problem not too long ago, but I’ve gotten quite a few letters about similar braking-system troubles since then, so it s time to revisit the matter. And the diagnosis is rather simple: Something is preventing the master-cylinder piston from fully retracting when the brake is released. There’s a small bleed hole in the bottom of the master-cylinder reservoir that connects to the cylinder s bore, and fluid can move to and from the reservoir only when the piston is fully retracted; as soon as the piston begins its stroke, the hole is essentially blocked. The hole serves two purposes: 1) As the brake pads wear, the caliper pistons move farther outward, so to compensate, the bleed hole allows additional fluid to enter the system as needed; 2) the hole also permits fluid in the braking system to reenter the reservoir when necessary—such as when the brakes are released after the fluid has expanded due to heat.

Normal braking can generate considerable heat in the rotors and caliper, which is transferred to the fluid within the caliper and the lower parts of the brake lines. This heat makes the fluid

expand, and if some of it can’t escape back into the reservoir via the bleed hole, it will cause the brakes to drag and eventually lock up, even if there is no pressure on the lever. Every time you release the lever, the piston is supposed to retract all the way, exposing the bleed hole and allowing some of the expanded fluid to return to the reservoir. Apparently, this is not happening on your Nighthawk. What’s more, when you park the bike after a ride, the brakes and brake fluid are probably a little hot, and because the fluid can’t bleed back into the reservoir, the pads are at least lightly pressing against the warm rotors. This heats the fluid even more, causing the brakes to lock. If you park the bike in a heated garage or in direct sunlight, the fluid might not cool enough before your next ride to allow

the brakes to release.

A number of things could be causing this problem. The components in the master cylinder may not have been assembled properly, or perhaps the frontbrake lever is not the correct one for that master cylinder. And even if the lever is the proper one, it may be hanging up in the lever perch just enough that it won’t return completely when released.

Here ’s an easy way to determine if the lever is the culprit. Next time you ride the bike, take along the tools needed to remove the front-brake lever, and when the brakes start to drag or lock up, immediately take the lever completely off the perch. If the brakes release, you’ll know that the lever is somehow at fault; if they don’t release, the problem is in the master cylinder, most likely with the piston.

Is Wetter better?

I ride my ’99 Honda Super Hawk yearround in Connecticut, so anti-freeze is a must during the winter months. Between April and October, however, I do a few days at a track that prohibits glycolbased coolants. My usual drill for track days is to drain and save the glycol coolant, refill with distilled water and Water Wetter for the track, then reinstall the glycol coolant when the

track day is done. After the last track day of the year, I flush the system and fill with new glycol coolant.

This process takes up time that I’d rather spend riding, so I would prefer to just leave the Water Wetter-amended water in the bike during the warm months. But the instructions on the Water Wetter recommend using at least 15 percent glycol-based antifreeze in street vehicles. Is there a downside to continuously running the Water Wetter mixture without glycol when there is no problem with freezing?

Bill Rath Oxford, Connecticut

Your Super Hawk’s cooling system should not experience any problems if filled with

water treated with the prescribed amount of Water Wetter. As a coolant, plain water actually is more efficient than a typical 50-50 solution of water and anti-freeze. Water Wetter improves that efficiency by breaking down water’s natural surface tension, further improving its ability to dissipate heat. Water Wetter also inhibits corrosion of the cooling system, including the aluminum of the radiator and cylinder heads. Unlike anti-freeze, however, Water Wetter does not lower water’s freezing temperature, which poses a potential summertime problem for automobiles. The air-conditioning system on a car or truck could possibly blow enough cold air through the heater core to cause the coolant in the core to freeze. To prevent such an occurrence, Red Line, the manufacturer of Water Wetter, recommends the use of 15-20 percent glycol-based anti-freeze. Unless your Super Hawk is equipped with air conditioning, this is not something you have to worry about.

Can’t get a grip

Can a tire have areas of greatly differing coefficients of friction? I’ve never been without a bike in 40 years, and my current one, a year-old dealer leftover, has almost low-sided me a dozen times, mostly at 5 mph or less. Initially, I attributed it to this bike being my first with tubeless tires running high pressures. Then I decided the tires just needed miles on them. At 1000 miles, I searched to see if the tires were subject to a recall; they weren’t. Now, at 3000 miles, I chalked the rear tire to see how much more lean was available and noticed that the chalk seemed to apply as one would expect on the right side, but the left side of the tire almost seemed like teflon, even though it was visibly identical. As a multi-decade reader of Kevin Cameron and owner of his wonderful Sportbike Performance Handbook, I knew that tires take a while to cure. It made me wonder if a new bike kept on its sidestand for an extended period might have a nonuniform cure. Bob Jones Lexington, Kentucky

You didn’t tell me the make and model of either the bike

or its tires, and I doubt that the dealer knows what might have happened to the rear tire between its installation at the factory and the bike’s delivery to you. All I can tell you is that there is no good reason the tire should be more slippery on one side than on the other. Some tire companies have made motorcycle tires that have softer rubber on the sides than in the middle, and even today, some special racing slicks built just for Daytona have three different rubber compounds. But no one makes a street tire that has different rubber on one side than the other.

Here’s the simplest, safest, most rational way to deal with your rear tire: Replace it. This is no time to cheap out. New tires aren’t that expensive, even top-of-theline sport rubber, and their cost is insignificant compared to the damage-to both you and the bike-that a tire-caused crash can incur.

Fight of the Vaikyrie

I just bought a 1998 Honda Valkyrie with 17K on the odometer, and it has a noticeable engine vibration during acceleration.

A local dealer said the vibration is due to poor carb synchronization, but since then, the bike has been serviced (carb cleanup and sync, all fluids changed, new sparkplugs, but no valve adjustment; the previous owner claimed that one was performed 5000 miles earlier), and that didn’t help. The engine pulls strongly, but it vibrates in any gear between 2800 and 4000 rpm. The vibration is felt mostly in the handlebar and has the same frequency as the engine rpm, so it is definitely not from the tires or driveshaft, and if I disengage the clutch, the vibration stops. The mechanic who did the service says he never saw a problem like this with other Valkyries. Could you advice me on this issue? Vlad Gur Atlanta, Georgia

I think your mechanic made a couple of mistakes in his diagnosis. For one, carbs that are out of synch would not cause vibration at higher rpm. The engine might run erratically at lower revs and smaller throttle openings, but if you didn’t notice any vibration under those conditions, you wouldn’t detect any farther up in the rpm range. The mechanic also erred by not performing a compression check. The procedure doesn’t take long, and it would have told you whether or not a tight or burned valve is the probable source of your Valkyrie s vibration. You don’t know for certain that the previous owner actually had the valves adjusted, or that the adjustment was done properly if it did take place. And even if it did, that’s still no guarantee that the valves are sealing properly 5000 miles later. So, before going any farther, have the compression checked, either by the leak-down or cranking-pressure method.

if the compression proves to be within spec on all six cylinders, check to ensure that all of the motor mounts are tight. This also is a relatively easy, inexpensive process that could cure the vibration altogether. If the mounts are secure, the next logical step is to check the primary and alternator drives. These contain rubber cushions and damper springs that may have broken or worn excessively, which would allow them to shake back-andforth and cause the kind of vibration you describe. If that fails to provide a solution, check the spring-loaded tensioner on the cam-drive belt; if the spring is broken, the belt couldflutter enough to cause small but constant changes in cam timing, resulting in engine vibration at certain rpm ranges.

Recall Roster

NHTSA Recall No. 05V151000 Harley-Davidson 2003-2005 FLSTC/I, 2003-2005 FLSTF/I, 2005 FLSTN/I Number of units involved: 110,000 Problem: The VIN/Certification labels on these motorcycles contain incorrect frontwheel tire-size and inflation-pressure Information. The label states that the tire size is MT90B21 and that the inflation pressure should be 30 psi, whereas the correct tire size is MT90B16 and the correct inflation pressure is 36 psi. Remedy: Harley-Davidson will mail installation instructions and a corrected federal certification label to all registered owners. If an owner so desires, a dealer can install the label. Owners who do not receive this free remedy should contact Harley-Davidson at 414/343-4056.

Free torque trick

I don’t have a problem but I do have a technical question. One of my riding buddies claims that an engine will make more torque if you adjust the valves more loosely than normal. Is this correct or just another of those myths that seem to go around? Donnie Hartwell Ft. Stockton, Texas

Generally speaking, your friend is correct, although the amount of improvement usually is quite small. Opening up the valve clearances to their maximum recommended specification causes the valves to open later and close sooner, effectively shortening the cam timing while also reducing valve lift by an amount equivalent to the increase in clearance. Depending upon the engine’s state of tune, this can boost torque by a percentage point or two but usually also lops off an equivalent amount of peak horsepower. This tactic won’tfill in flat spots in the torque curve but it can marginally sharpen the bottom-end performance. On most bikes, however, the differences would be too small for the rider to notice. Plus, you have to adjust the valves more frequently because the clearances already are at the far end of their acceptable range. For 99 percent of all riders 99 percent of the time, it ’s not worth the time and effort.

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.