Service

SERVICE

Half-braked idea

I have a 2002 Yamaha R1 that is stock as far as the engine is concerned. I had aftermarket brake lines installed and removed the right-side front-brake rotor so it would be easier to see my red translucent powder-coated wheels. This type of wheel treatment is the trend around Columbus right now. Can you tell me how much braking distance or braking time I will be losing at various speeds compared to the stock two-rotor system? I want to know how safe or unsafe my one-rotor brake is before spring hits. If it’s too dangerous, I will reinstall the second rotor and caliper. Kevin Chan Columbus, Ohio

Many motorcycles are built with just one front disc brake, and they re able to slow and stop without any problems whatsoever. The difference between those bikes and yours is that they were engineered to have just one front brake, whereas yours was designed to have two. By removing one of your RI ’s brakes, you eliminated one-half of the front-brake swept area and altered the balance between brakecaliper fluid volume and master-cylinder mechanical advantage.

All other factors being equal, a single-rotor brake system uses a smaller master-cylinder piston than a dual-rotor system. The diameter of the piston is calculated to provide the necessary mechanical advantage while moving only the volume of brake fluid necessary to operate one caliper. If a second rotor and caliper are added, the diameter of the master cylinder usually is increased because the piston now has to displace more fluid to operate two calipers. If the piston diameter remains the same, the brake lever will have to travel too far to make the brake engage. A bigger master cylinder provides less mechanical advantage than a smaller one, but that loss is more than offset by the increase in swept area brought about by the addition of a second rotor.

I don’t have any hard numbers or charts that can predict the changes in your Rl’s braking characteristics, but I doubt you will experience any behavior that could be termed “dangerous.” It’s my guess that your R1 will still be able to stop just as quickly as before, but that you’ll have to squeeze the lever a lot harder to make it do so. I also suspect that it won’t be capable of as many back-to-back stops from high speeds without noticeable fade. That, in fact, is the main reason most sportbikes, roadracers and other high-performance streetbikes are equipped with dual front disc brakes: to make braking easier, more consistent and less prone to fade during continual stops from high speeds.

I suggest you find a safe location where you can try making hard, panictype stops on your R1 and see for yourself how it behaves with just one front rotor. If you can’t make the front wheel approach lock-up with a reasonable amount of lever pressure, I’d strongly suggest you put the other rotor back on and forget about how cool you look; after all, how cool do you think you ’ll look in a full-body cast?

The need for speeds

I own a ’96 Kawasaki Vulcan 1500 Classic, which has a four-speed transmission. I have the opportunity to purchase a fivespeed transmission out of a later 1500 and was wondering if it is possible to remove the four-speed and replace it with the five-speed. Dave Dyer Kansas City, Missouri

Yes, the transmission from a later fivespeed Vulcan 1500 will fit in the earlier model ’s four-speed cases, but the switch involves more than just the addition of another gearset; this conversion requires the replacement of every single component in the four-speed box with those of the five-speeder. Under normal circumstances, the sheer expense of all the required parts could make such a swap cost-prohibitive; but if you’ve located a good used gearbox at a price you can stomach, that ’s not such a concern. If you aren’t capable of performing the work yourself, however, you ’ll have to pony up for all the labor charges required for an engine teardown and reassembly.

Considering that one way or another, this swap is going to cause you some expense, I can’t help but wonder what is prompting you to do it in the first place. The Vulcan 1500 has such a wide, seamless powerband and enough lowand middle-rpm torque that it’s not in desperate need of another gear ratio. Kawasaki added a fifth gear, I believe, more for marketing reasons than for any performance gains. So the question here is not whether or not you want a five-speed transmission in your Vulcan; the question is, why do you want it?

Falling Stars

I need to know what is going on with Yamaha regarding a recall of Road Star models because of a problem with the transmission that can cause the rear wheel to lock up. I own a Road Star and so do quite a few other riders I know, and we all are very upset about the way this problem is being handled. We’ve been told the problem is serious enough that we should not ride our bikes, but the dealers are having a hard time getting the parts kits needed to make the repairs. My dealer said he > could only rebuild two motors a week, and I am number 27 on his list. Some of us are still making loan and insurance payments on bikes we can’t ride. Please help if you can. Cory Dionne Merrimack, New Hampshire

I don’t know if I can “help,” since this is a dilemma that exists between Yamaha, its dealers and its customers, but perhaps I can shed a little light on the matter. On January 9, 2004, Yamaha issued a technical bulletin describing a voluntary recall campaign the company was initiating to remedy a potential transmission failure. According to the bulletin, a quality-control problem with certain transmission parts on all 2002 and 2003 Road Star models can lead to abnormal wear which could cause the failure of a circlip that holds one of the gears in place. When the clip breaks, that gear can slide far enough to one side to put the transmission in two gears at once. Not only would that lock up the transmission and the rear wheel, but disengaging the clutch wouldn’t allow the rear wheel to stop skidding. If the bike were making a turn or moving at any speed greater than a walking pace, the end result could easily be a crash.

Yamaha claims that only a very tiny percentage of Road Stars have been affected by this problem, but the serious consequences of a possible failure obligate the company to modify every one of them. The remedy involves a complete engine disassembly and installation of a special 4th Pinion Gear Exchange Kit that contains a total of 41 separate pieces. The kit includes not just the affected gears and shafts but also all the necessary gaskets, clips, washers and seals required to do the job.

Worldwide, somewhere around 30,000 Road Stars are affected by this recall, and the need to quickly manufacture such a large quantity of parts initially held up delivery of the kits. But Yamaha claims that all the required kits will have been shipped to dealers by the end of April, and that all 2004 Road Stars have been suitably modified at the time of manufacture. Hopefully, then, by the time you read this, your Road Star will already have been repaired.

In a classic case of making lemonade out of lemons, some enterprising Yamaha dealers have prompted their Road Star owners to use the transmission repair as an opportunity to hop-up their engines at a vastly reduced cost. Since the engine has to come completely apart anyway, it can be reassembled with aftermarket hotrod parts at little or no labor cost to the customer; the labor is paid by Yamaha, making the customer responsible only for the cost of the speed equipment. Yamaha has no problem with this practice and is even paying its dealers 91/2 hours worth of labor charges for a job that s only listed in the flat-rate book for 7!/2 hours.

Spaced out

I just finished installing new rear wheel bearings on my ’97 Yamaha YZF600R, but something isn’t right. Every time I try to tighten the axle nut, the rear wheel refuses to turn. If I back off the nut just a little bit, the wheel will spin freely, but as soon as I apply even a little bit of torque to it, the wheel freezes solid. I know that I’m not overtightening the nut. I borrowed a torque wrench and checked the torque on the bike’s front axle nut and it was 62 lb.-ft., but the rear wheel locks up with anything more than about 15 lb.-ft. on its axle nut. Everything was okay before I changed the bearings, so what did I do wrong? Ricky Cheshire Muncie, Indiana

You probably made one of three mistakes: You may have failed to press one (or both) of the new wheel bearings all the way into its respective mounting bore; you could have forgotten to reinstall the spacer tube that fits between the two bearings; or you may have omitted the little spacer that goes between the sprocket hub and the left-side wheel bearing. Any of these miscues would result in the same symptoms, but I’ve found that failing to put the spacer tube between the wheel bearings is the most common oversight.

Recall Roster

NHTSA Recall No. 03V521 American IronHorse Legend, Outlaw, Ranger, Slammer, Stalker, Tejas, Texas Chopper, Thunder Model year: 2002-2004 Dates of manufacture: Aug. ’01-Nov. ’03 Number of units involved: 2395 Problem: On certain motorcycles equipped with optional brake-rotor carriers, the carriers can crack while in service and possibly break, causing partial loss of the brake system or the potential for rotor-carrier detachment, either of which could result in a crash. Remedy: Dealers will replace the rotor carrier assembly. Owners who do not receive the free remedy within a reasonable time should contact American IronHorse at 817/665-2045. NHTSA Recall No. 03V535 Big Dog Chopper Model years: 2003-2004 Number of units involved: 1446 Problem: On certain motorcycles assembled with an early-version Rolling Thunder frame, a stress crack could develop in the frame, which could cause the rider to lose control of the motorcycle. Remedy: Dealers will repair the frame. Owners who do not receive the free remedy within a reasonable time should contact Big Dog at 316/267-9121. NHTSA Recall No. 03V525 Triumph Speedmaster and America Model years: 2002-2004 Dates of manufacture: June ’01-Dec. ’03 Number of units involved: 5148 Problem: If the motorcycle is dropped onto the left side, air may enter the rearbrake master-cylinder reservoir. If the reservoir is not checked after the tipover, the rear brake may not operate, resulting in a loss of control and increasing the risk of a crash. Remedy: Dealers will reposition the rearbrake master cylinder. Owners who do not receive the free remedy within a reasonable time should contact Triumph at 678/854-2010.

Tightening the axle nut draws together all of the separate components (spacers, wheel adjusters, inner bearing races, the swingarm itself, etc.) that the axle passes through. If any of those components are missing or not situated precisely where they are intended, tightening the axle nut will either cause the wheel to bind or allow it to have excessive side-to-side freeplay. If you didn’t get the bearings pushed all the way into the bottom of their mounting bores, tightening the axle will squeeze the inner bearing races closer together while the outer races remain where they are. The bearings are designed only for radial loads and not side loads, so this pinching shifts the inner races out of lateral alignment with the outer races, binding the bearing and locking the wheel. The same thing happens if you omit the spacer between the bearings; the spacer prevents the inner races from being squeezed closer together as the axle is tightened, so without it, the bearing binds and the wheel locks.

Remove your YZF’s rear wheel and check these components very carefully. Stick a finger through the inner race of one of the wheel bearings and try to feel the presence of the spacer. If it is in place, you 'll then need to verify that the bearings are fully seated. Using a hammer and a drift, tap on both bearings ’ outer races (not the inner races), changing your point of impact by moving around the race after every couple of taps. Do this until you are sure that both bearings are fully seated in their bores.

Here are two additional pieces of relevant information: The correct torque specs are 85 lb.-ft. for the rear axle nut and 47 lb.-ft. for the front axle, not 62 lb.-ft; and never install any bearing that mounts on its outer race by hitting or pushing on its inner race, and vice versa. Otherwise, the installation process will inflict damage on the bearing that could prove terminal.

Got clearance?

I’ve asked several mechanics this question but never gotten the same answer twice: Why do valves have clearance or “lash,” and why isn’t it the same for all valves and all engines? I’ve noticed that some engines require more valve clearanee than others, and some engines even have different intake and exhaust clearances. I’m hoping you can shed some light on this for me. Matt Stafford Warrendale, Pennsylvania

Hey, that’s two questions, not one. But you ’re in luck: We ’re running a two-forone special this month, so I’ll answer them both.

It’s all a matter of heat expansion. There always needs to be at least a minimal clearance between the top of the valve stem and the device that pushes on it (cam lobe, rocker arm, follower, etc.). Were there no clearance, the valve would not fully close, allowing that cylinder to lose compression. For convenience and consistency, the clearances are adjusted when the engine is cold, but under those conditions, they are greater than they will be once the engine reaches full operating temperature. As the engine heats up, the cylinder head and its valvetrain components all expand, but not all at the same rate. A valve tends to expand more than the other components, since one end of it lives in the combustion chamber, where the heat is generated. Since the valve grows more than the components around it, the clearance is reduced as the engine heats up. During the R&D process, the engine designers figure out how much clearance the valve needs when cold so it will still have at least some clearance when hot.

But wait! There s more. Not only is the face of the exhaust valve subjected to the heat of combustion, the entire head of the valve and the lower part of its stem get blasted by hot gases rushing out the exhaust port. Meanwhile, the intake valve gets cooled slightly every time a fresh fuel charge passes it en route to the combustion chamber. As a result, the exhaust valve tends to run hotter than the intake valve. On some engines, this calls for the exhaust valves to have slightly more cold clearance to ensure that there will be sufficient clearance when hot.

Who let the dogs out?

I have a 1992 Kawasaki ZX-7R that I just bought used with only 10,000 miles on it. I got it pretty cheap because it had a major problem with jumping out of second gear, just like described in a Service response to Keith Graham (“Put a fork in it,”) in the January, 2004, issue. I have some experience with motorcycle engines, so I took mine apart to fix it myself and couldn’t believe what I found: One of the gears that engages second only had two dogs on it! It’s supposed to have four, but the other two were completely gone. If you think that’s weird, I couldn’t find any pieces of metal in the oil that were big enough, even if all the little filings were glued back together, to account for just one of the missing dogs, never mind two of them. The remaining dogs on that gear and the four on the mating gear were all beat to hell and rounded off, and the shift fork was bent, so I had to replace all that stuff anyway. But I can’t figure out how the dogs broke off and where they went. The rest of the tranny looks just fine, with no evidence that the broken-off pieces got chewed up by the other gears. Got any ideas? Benny Salazar Posted on www.cycleworld.com

Yeah, I do. I believe that the phantom dogs were missing when you bought the bike. I think that a previous owner, for reasons I couldn’t even begin to understand, cut the dogs off and put the gear back in the transmission. Maybe he did it so he could unload the bike without having to buy a new gear. Maybe he thought it was some kind of trick modification that would allow the gearbox to shift faster or easier. Maybe he was just an idiot.

Whatever the case, it is virtually impossible for just one or two gear dogs to break off entirely and leave the others intact. All the dogs make contact simultaneously, so they share the forces applied to them equally. It only makes sense, then, that any force powerful enough to shear off one or two of them would do likewise to all of them. The absence of shrapnel in the gearbox is another clue that someone deliberately installed the gear in question and that it may not have lost its dogs by accident. While you have the engine apart, you d be well served to check everything else to ensure that the same “mechanic ” hasn’t butchered something else.

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 949/6310651; 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.