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.
MONOSHOCK STIFFNESS
I recently bought a 1978 Yamaha IT175 with 2150 mi. on it. Everything works fine except the monoshock. Being a 170 lb. rider, I like a slightly stiffer suspension. Both ends of my bike supply this, so fast riding and jumps are no problem. After a jump the landing is soft, but for some reason the monoshock will not return as normal. Instead it takes many seconds for it to come back out. The monoshock could have been adjusted for a stiffer ride because jumps are about the only time the shock will work or move. Also, when I get off the bike the monoshock will very slowly creak back out to its normal position. This creaking is loud and the problem is altering suspension performance.
Is it possible to repair this problem? If so, how much would such a repair cost in relation to a new monoshock?
Chris Bennett Germantown, N.C.
The problem is likely to be in the mono shock, but before you spend time or money on the shock, remove it and make sure the swing arm works freely. A bent swing arm or bad bearings can sometimes cause the symptoms you describe. If the swing arm is all right, the monoshock needs work. It is possible that the previous owner has the damping clicker adjusted in too far, which will virtually close off oil flow on rebound and prevent the shock from returning to normal position. Try returning the damper adjustment to the medium position as specified in the owners manual. If there is still no improvement, the shock has either a bent damper rod or it is worn out and has lost the nitrogen pressure it needs to return properly. It will have to be replaced or rebuilt. A new shock, without spring, from Yamaha lists at $107.46. A cheaper alternative is to have it rebuilt by White Bros. Cycle Specialties, 11611 Salinaz Dr., Garden Grove, Calif. 92643, (714) 638-1653. Charge for a straight rebuild on the IT monoshock is $50. For $95 they can rebuild the shock and tailor it to your specific needs in weight and riding conditions, adding new springs, valving and sleeves. Rebuild time is two days in shop.
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KAWASAKI CALIPERS
I have a ’74 Kawasaki 500 H-l. This bike has the front disc brake caliper in front of the fork leg. A friend said that it should be behind the leg to increase braking power and limit diving under severe braking pressure. He said to slide the forks out of the clamps and turn the whole assembly 180° to accomplish the job.
Is there anything to the line he’s giving me? Can the front forks and wheel be turned like that? As I’m not a professional rider would I gain that much by doing it? All the other bikes I see have the calipers behind the leg except for mine and a few Harleys. What gives? Style? Function? Safety? Efficiency?
C. Rodebauge Durham, N.C.
In theory, placing the caliper behind the fork leg moves the mass of the caliper closer to the steering head axis, which gives the fork assembly a lower polar moment of inertia as it swings on its axis. A popular explanation of this principle says that if you hold a barbell by the center of the bar and twist it back and forth, the change of direction will be easier as the weights are moved closer to your hand. In motorcycle application, moving weight closer to the steering axis should make for lighter steering and better steering control when road conditions try to amplify fork vibrations into a tank slapper.
However. There is a second school of thought which maintains that the higher polar moment of inertia gained by moving weight away from the steering axis actually helps prevent steering wobble by resisting deflection and helping to damp road vibration in the first place. Thus you have the Honda Gold Wing (admittedly no sport bike) with weighted handlebar ends. On racing bikes, there is also cooling to consider, and brake calipers stay cooler when they are in the undisturbed air flow in front of the fork leg. So on competition machines the question of fore-or-aft caliper mounting seems to have become academic. Some of the best handling, fastest bikes in the world have a pair of calipers sitting in front of the fork legs: Barry Sheene’s World Champion RG-500 Suzuki, this year’s Daytona-winning Yoshimura Suzuki Superbike, the Honda RSC1000 and the Moriwaki Kawasaki. Our resident Superbike racer rode the Moriwaki bike with the calipers both ways and said there was no detectable difference. Two of the 400F Hondas we’ve raced, calipers in front of the forks, handled very nicely without brake modification.
Moving the caliper on your H-l will probably not make a substantial change in the bike’s handling, except perhaps to lighten the steering on an already light and quick steering bike. It will not increase braking power or limit dive. Kawasaki engineers were free to place the caliper on either side of the fork leg when they designed the bike and no doubt placed it in front with the H-l’s particular handling and steering characteristics in mind. If you want to try it, however, the forks can be turned 180°. Re-routing of the brake line will be necessary and the fender will have to be repositioned; the speedometer will no longer work, with the drive running in reverse.
Our feeling is it’s probably not worth the trouble. And in the case of the H-l, any small bit of weight you can move farther forward will probably help the tire touch ground occasionally between shifts.
CBX RATTLE
Okay, guys, figure this one out. My 1979 Honda CBX makes a grinding rattle which seems to be originating under the clutch cover and occurs only between 500 and 1500 rpm (right at idle). The noise fades slowly when the clutch is disengaged and stops instantly when the transmission is clunked into gear.
One dealer said primary chain, another said primary drive gear, and American Honda says the clutch basket is rattling on its rivets; but with a little study and disassembly, none of those explanations seems to make sense.
My guess is the steel driven clutch plates rattling on the splines of the inner clutch hub. Am I right? And if so, why don’t other motorcycles of similar design do the same? Can the noise be eliminated? Is it really as “harmless” as American Honda indicates? It sounds bad enough to make me grit my teeth!
J.M. Ganzer
San Rafael, Calif.
Your guess is correct, but the others are also partly right. Most of the noise you describe is clutch plate rattle in the basket, but there is also a bit of grumbling from the straight cut jackshaft gears, Hy-Vo primary chain and from the driven primary sprocket where it is splined to its shaft. The 1980 CBX has a tapered collar on the driven sprocket to eliminate that contribution to idle noise, but the labor and cost of changing over a 79 to the new setup would probably not be worth the small improvement. The noise occurs only> when there is no load on the engine, and even the small amount of drag from the disengaged clutch plates eliminates most of it. This rattle, though occasionally bothersome, is, as American Honda says, harmless. The best way to quiet it down is with accurate carb synchronization at idle.
A rough idle causes drive train vibrations that load the sprockets, gears and clutch unevenly and amplify the noise.
XS750 OIL COOLER
I have long been skeptical of the need for fitting an oil cooler to motorcycles that are used for non-competition riding, but after increasing the displacement in my Yamaha XS750D it seems to run noticeably hotter, and I’m wondering if an oil cooler isn’t a good idea now. I’d appreciate your thoughts on the approaches open to me.
Late models of my machine do have a cooler fitted, and I suppose I could purchase the necessary bits and pieces and retro-fit them to my bike. Past experience has taught me that owning “genuine Yamaha replacement parts’’ can be an expensive proposition, and I am naturally considering an aftermarket cooler. Yamaha feeds its cooler from a plate located between the oil filter and the crankcase, while some aftermarket items use the external oil line that supplies the camshafts in the head. Since Yamaha has not provided replaceable bearings for these cams it would appear that a momentary loss of oil or an oil pressure drop would mean replacement of the entire head. Is this a valid concern? Which cooling system is superior?
Lawrence Erkie
Los Angeles, Calif.
The best way to determine if a cooler is needed is to install an oil temperature gauge. Performance modifications often cause running problems which are due to minor jetting, flow or ignition irregularities rather than an overheated engine. Only an oil temp gauge will let you know if there is a problem. Running the engine too cold is nearly as bad as the other extreme because the oil will not flow at its proper operating viscosity and it will retain moisture and acids normally evaporated off at higher temperatures. Generally 160° is accepted as minimum healthy operating temperature, 180° to 200° ideal, and anything up to 250° acceptable for heavy loads, hard running or competition. Above that, most oils begin to oxidize at an accelerated rate.
If you have doubts about your running temperature a temp gauge is a good investment because it will either dispel or confirm your worries. If the engine is in fact running hot and you decide to fit a cooler, a gauge will measure the drop in tempera-> ture and also warn you if the oil becomes too cool. In winter weather, for instance, it is often necessary to cover the oil cooler (unless it includes a thermostat) to maintain correct operating temperature. Most oil temp gauges use a sensor which replaces the oil sump drain plug. VDO-Argo Instruments, 980 Brooke Rd., P.O. Box 2630, Winchester, Va. 22601 manufacture a dial-type gauge, and digital readout oil thermometers are available from Kerker/ Kendrick Engineering, 7900 Deering Ave., Canoga Park, Calif 91303, or from Hayden, Inc., 1531 Pomona Road, Corona, Calif. 91720.
If high temperatures necessitate your buying a cooler, the Yamaha item is probably the most expensive way to go. They no Jonger make a regular kit for the 750, but a retro-fit from the 850 is available. The Yamaha cooler, with oil lines, hardware and adapter will cost $200. Hayden, Kerker and Lockhart, however, all make XS750 coolers with a sandwich-type adaptor for oil pickup between the filter and cases. The Hayden cooler lists for $113.30 in chrome and $82.20 in black; they have a separate thermostat for $40, at the address listed above. Lockhart makes two coolers for the 750, small and large,
for $89.95 and $104.95 respectively. The large cooler can be bought with a built-in thermostat for $134, or a separate thermostat is available for $34.95, at Lockhart Industries, 16606 Texaco Ave., Paramount, Calif 90723. Kerker/Kendrick Engineering sells an XS11 oil cooler kit which they say will fit the XS750 for $92.35, thermostat kit $35 extra.
The chief advantage to coolers with the sandwich pickup at the filter is that they are a full-flow design; all of the oil in the system goes through the cooler, so overall oil temperature is lower than with systems which use a pickup off the oil line to the cylinder head. They are also easy to install because no threading or other modifications are needed to bolt on the pickup.
Coolers which tap off an oil line to the head cool only a small portion of the engine oil, but manufacturers are quick to point out that the cylinder head runs hotter than other parts of the engine and the cams and valves benefit most from lower temperature lubrication. These coolers will cause a slight delay in oil delivery to the upper end when the engine is first cranked over, usually from 1 to 1.5 sec., a time period which is probably not significant when there is residual oil on the cams and buckets. All coolers drain down somewhat when the engine is shut off and have to refill to come back to full pressure. Operating oil pressure is not affected by most coolers because oil gallery restriction in the engine is greater than that in the cooler or external lines. An oil cooler with its pickup taken off the cylinder head oil line is made by Derale Oil Cooler, 138 W. Gardena Blvd., Gardena, Calif. 90248, for $79.95 with thermostat and $69.95 without.
Again, check your oil temperature be-> fore installing a cooler. If it is within normal operating range, you are better off without one.
TOO TALL
I have been following your service column closely for some time, waiting for someone to come up with my problem, but with no luck. j
As the proud owner of a 1978 Honda 750F I have only one complaint. The bike is too high for me. I have to risk picking it up at stop signs every time I lean the bike over to put it in gear. I have replaced the seat for a lower one, which helped a little, but was wondering if there are rear shock modifications or any other means I could use to lower the bike.
B. Santa Cruz Woodland Hills, Calif.
Shorter rear springs, both aftermarket and those for other Honda applications, are available for the 750 in a variety of spring rates. The simplest and least expensive answer, however, is probably to install a lowering kit. Most kits contain a pair of blocks that bolt into the lower shock mounts and allow the shock to be mounted rearward a few inches, which raises the swing arm and effectively lowers the back. of the bike. With a lowering kit in place the pinch bolts on the triple clamps can be loosened and the front fork tubes slid upward to lower the front end a corresponding amount, bolts tightened when the bike is level.
Honda 750 lowering kits are available from Domi Racer Distributors, Inc., 52181 Wooster Rd., Cincinnati, Ohio 45226 FOR.L $7.95. Rocky Cycle Co., Inc., 1250 Elko Drive, P.O. Box 1431, Sunnyvale, Calif. 94086 also sells a kit called “Shock Backs” which will lower the rear suspend si on for $15.10.
SALT PITS
Being a Florida biker, I speak for many others who have this problem. The problem I am speaking of is pitting of the aluminum on our bikes from salt and sand from the road and air. I had a similar problem with my ’78 Wing on Long Island. I solved this with chroming the belt and valve covers. But with my ’79 XS1100 I don’t want to go through the expense of chroming the front forks, engine side covers and cam covers. Is there anything w<* can use on our exposed aluminum, like black paint, to repair or at least protect the rest of our bikes? It’s the pits.
Michael K. Corcoran Boynton Beach, Fla.
Wish we could give you the name of the miracle product you need, as bikes in th& CW office area also suffer from salt air. Salt does a thorough job of attacking and , pitting nearly any metal surface not encased in plastic, cosmoline, or some other thick film that renders motorcycles useless for anything but storage. We checked with tBrian Slark, whose coastal area business is the restoration and preservation of classic bikes. His advice: ( 1 ) Keep the motorcycle covered or garaged at night or when' ever you aren’t using it. (2) Make sure that metal and painted surfaces are heavily waxed, and (3) Wash the salt film off the fiike with clear water at every opportunity. Any coating over a vulnerable surface— car wax, paint, or one of the silicone or polymer-based finishes—is better than nothing. These will provide a temporary barrier to salt corrosion, but only frequent washing will keep it from pitting through. Even these precautions will not eliminate salt attack but should minimize the damage.
SHIMMY FIX
Just read the first letter in the Service column in the May, 1980, issue, from Morris Hammack, Whitehouse, Texas. "My GS850 had an identical wobble or shimmy at 32 to 40 mph. Three relatively good Suzuki service shops could not help -me. Because I had tried everything you suggested plus some, I figured I had nothing to lose, so took about one-eighth turn on the steering head bearings.
Shimmy went away completely!
This was done in May, 1979. There was no detectable looseness prior to this adjustment and the front end did not become -overly tight. Please forward this information to Mr. Hammack post haste so he can get the world’s finest sports tourer down the highway shiny side up.
T. Herr
South Haven, Mich. £1
