Service
SERVICE
We welcome your technical questions and comments, and will publish those we think are of interest to our readers. Because of the volume of mail received, we cannot return any personal replies. Please limit your “Service” letters to technical subjects only, and keep them as brief as possible. Send them to: “service,” CYCLE WORLD, 1499 Monrovia Ave., Newport Beach, Calif. 92663.
HIGH SPEED WEAVE
My 1982 GSI 100E is a great bike, but in high speed sweepers it wobbles as if it were hinged in the middle. It does fine in a straight line but in the corners it’s wicked. The only change from stock is a set of the new Dunlop Sport Elite tires. I have set and reset my suspension and nothing seems to help. I know a lot of guys that have bikes that wobble and they figure all bikes wobble. I don’t! Any help would be useful.
Herb Abell
Loma, Mont.
The problem you are describing is a classic case of what the motorcycle dynamics technical literature describes as high speed weave. High speed weave is characterized by a coupled pitch-rollyaw oscillation, and does feel like the motorcycle has developed a hinge, or as if the bike is doing a snake dance underneath you.
Well assume your GS didn’t weave before you made the tire change. If this is the case, you should look for causes related to the tires or the wheel removal and reinstallation. The first thing to check is tire runout. The Dunlop Sport Elites are large tires and they may not be perfectly centered on the rims. You can check for runout by putting the bike on the center stand and spinning the wheels. Vertical runout of either tire should not exceed 0.1 in. If it is greater than that, you can probably correct it by deflating the tire and resetting the bead. Once you’re sure the tires are properly mounted, you can check the wheel alignment. This would also be a good time to check for any obvious loose pivot points, mainly to eliminate any concern that they may be contributing to the problem. The steering head bearings should be adjusted to factory specifications, and there should be no play in the swing arm (either side-to-side or in twisting).
If you haven’t come across any obvious problem yet, and your bike still weaves, the time has come to look at the suspension. Return the suspension to the factory recommended settings, and back off the preload. If the motorcycle still weaves, try increasing the damping at both ends. Do the rear shocks seem to be doing their job, or does the rear end feel “springy”, with the bike oscillating up and down several times after passing over a dip in the road? This is important because of the interaction between pitching on the suspension and the weave. Shock and fork damping are the main energy drains from the pitch-weave interaction, and loss of this damping will make things worse quickly. Our experience is that the GS1100 shocks lose much of their damping capabilities after several thousand miles, so perhaps your bike is in need of new shocks. If these changes have cured the high speed weave, you could, if desired, increase the preload and air pressure settings in the fork and shocks. If the weave reappears after doing this, at least you have settings that work to return to.
Alternatively, if the weave is still there, you’ll have to consider the possibility that the Dunlop Sport Elites themselves are the source of the problem. Not all tires work with all motorcycles, and the stiff construction Dunlops have characteristics very different from the O.E.M. tires the Suzuki was designed to use. Perhaps, if all else failed, a tire switch would eliminate your handling problem.
STURGIS BELTS
I am interested in buying an FXB Sturgis Harley-Davidson, which is belt driven. I would like to obtain information on the wear and durability of the belt as compared to a chain. Could you help me?
Joe Mobley
Boulder, Colo.
We’re not sure if we can be much help in giving you a service life of the final drive belt on a Sturgis because we couldn’t find one that had failed in normal use. We did hear of one that had been damaged when a rock had been trapped between the belt and sprocket when the bike was being used on a gravel road, but even that belt survived long enough to carry the bike and rider to a dealer for a replacement. Harley representatives will only say that they expect at least a 20,000 mi. service life from the belt. Local dealers are less pessimistic since they have seen no belt failures and some of their customers have more thani
40.000 mi. on a Sturgis.
The primary belt has not had such an outstanding service history. There were some cases of belt failure after relatively few miles on the original 1980 Sturgis models, and there were occasional complaints about noise when a loose belt rubbed against the cases. Also, the compensator sprocket used on the 1980 models had some durability problems, and often needed repair after
10.000 mi. Reacting to these problems, Harley has updated the compensator sprocket with hardened thrust washers, and incorporated provision to adjust the primary belt tension. These changes have improved matters to the point where local dealers expect 20,000 mi. on the primary belt. However, these same shops recommend the replacement of the primary belt at the 20,000 mi. mark as preventative maintenance.
TRAIL AND RAKE
I’ve been reading your reports on various street bikes for a while and think they’re great, but could you please explain what rake and trail are and how they affect steering?
W. Wright
Costa Mesa, Calif.
When looking at a side view of a motorcycle, rake is the angle between the steering axis (the centerline of the steering stem as it turns in the headset bearings) and a vertical line. Trail is the distance the center of the front tire contact patch (directly beneath the front axle) is behind the point where the steering axis intersects the ground.
The affect of trail and rake on steering is complicated, but, in general, more of either will lead to more straight line stability and heavier steering. Notice that both rake and trail can be changed by suspension movement, so the actual values during riding may be different than the quoted values which are measured with an unladen machine. In addition, there are other factors affecting steering characteristics, such as tire construction and profile, front wheel weight and inertia, wheelbase, weight distribution fore and aft, center of gravity height, and moments of inertia of the motorcycle. Because of the complexity of the situation, rake and trail comparisons are only useful between very similar motorcycles on similar tires.
WARPED BRAKE ROTORS
In July of 1981 I purchased my CB900F. Since then I’ve placed 6000 mi. on the machine, riding 110 mi. to and from school with a lot of hard back road riding. At about 3000 mi. I started getting a pull out of my front brakes, not left or right, just grabbing when the brakes are applied. This was more pronounced at slower speeds than higher speeds. At 5800 mi. it got really bad. My dealer said that the brake discs had warped under hard braking and that this time they would be replaced under warranty, but next time it would be my wallet that buys them. The rotors and brake pads cost $400!
How can this be, a design flaw in a cycle that is supposed to perform under hard conditions? It’s such a beautiful bike in all other areas; what’s the catch? Did Honda put too small rotors on the front? If so, is there an aftermarket product I must use to get better results? My dealer says with the stock parts being used the condition will just reappear. What’s up?
Robert M. Prado
Sumter, S.C.
We discussed your brake disc warpage problem with American Honda, and they may be of some help to you. Their one-piece brake discs and carriers have gone through a number of redesigns and process changes through the last five years, and they claim the incidence of rotor warpage for 900Fs is low. They suggested that if you have problems with your new rotors, you should either have your dealer call their warranty hot-line, or that you directly contact their Customer Services Office at (213) 321-8680. If your brake rotors were warping under hard street use, the American Honda representative thought arrangements could be made to replace the rotors at their expense.
As general advice to anyone who has suffered a problem during the warranty period that then reoccurs after the warranty is over, we would suggest that they contact the manufacturer, or the manufacturer's local service representative, politely, in writing, as soon as possible. From our experience, this is often all it takes to achieve the desired repair. If you can’t get satisfaction from this approach, don’t despair. While we’re not lawyers, we believe that the right to have a motorcycle fixed extends beyond the warranty period for problems brought to attention during the warranty period. The best place to find out specific legal information about warranty rights would be the state level consumer protection agency or office. After that, it's up to you.
