Service
SERVICE
PAUL DEAN
Meshing, not mashing
In John Agugliaro's "Leaping to contusions" letter in the October issue, which dealt with the problem of the clutch plates sticking when he shifts his older Honda into first gear before each ride, I can’t believe you did not suggest he simply hold the front brake on before putting the bike in gear. That will stop the bike from lunging forward and break the clutch loose; it instead kills the engine without the leap. Then, he just has to put it back in neutral and repeat the process until it goes into gear smoothly. I’m betting one time will be enough.
Leon Sizemore Posted on www.cycleworld.com
I’ve gotten dozens of responses to that Service letter from readers who suggest all kinds of solutions to Mr. Agugliaro’s problem: rocking the bike back-and-forth in gear before starting; starting the engine in gear with the clutch lever fully compressed; putting the bike on its centerstand in gear and turning the rear wheel by hand; lashing the clutch lever to the twistgrip at the conclusion of each ride so the plates can’t stick together before the next ride; and various forms of your suggestion to use the front brake to prevent the bike from lunging forward.
Problem is, none of these suggestions cure the problem; they instead just treat the symptoms. That’s not what I do in Service. There often are countless ways to work around a malfunction, but my goal here is to cure problems, not sidestep them.
Besides, many of those temporary “fixes” don’t always work or even can cause other problems. Not all motorcycles have centerstands, for example, so that tactic won’t always work, and starting the engine in gear often fails to break the plates loose; it also can cause the bike to move forward and possibly even start the engine, which could have disastrous results. Rocking the bike back-and-forth in gear before starting may or may not work, either, depending upon how firmly stuck together the clutch plates might be; and while tieing the clutch lever to the grip after a ride will prevent the plates from sticking, it also can weaken the clutch springs by fully compressing them when hot and holding them in that position for long periods. Intake and exhaust valves are randomly held in an open position when an engine is shut off; but their springs are made of a specialized, high-grade metal through an elaborate manufacturing process so they can resist weakening when cycled tens of millions of times and held fully compressed when hot; clutch springs, however, usually are of a lesser quality, especially in many older engines.
Finally, your suggestion of using the front brake to prevent the bike from moving forward does not necessarily work, either. I have dealt with many bikes that had this same clutch problem, and in some cases (especially on slick, polished concrete surfaces, such as in home garages, gas-station pump areas, parking-lot/garage floors, etc.), they would still lunge forward with the front brake locked. This is especially true when starting an engine cold (which is when this problem usually occurs), because the idle speed is likely much higher due to the use of the cold-start/choke mechanism. I once saw a rider slam into the side of a parked car when he dropped his bike into gear with the front-brake applied, and I witnessed another instance in which the rider lunged into a person walking in front of the bike.
What’s more, shifting into gear when the clutch fails to disengage damages the transmission. The sudden shock of two gears’ sets of engagement dogs clashingone set stationary and immovable, the other spinning at three, four, maybe five hundred rpm and instantaneously being slammed to a complete stop-can round off gear dogs and bend shift forks. It also delivers a severe shock to the entire drivetrain, from the primary drive to the rear wheel and everything in between. Your method might be acceptable if the clutch plates only hung up lightly every once in a while; but for a severe, everytime condition like that experienced by Mr. Agugliaro, repair or replacement is the only sensible solution.
The plane, the plane
After reading your response on the "Science of sipes," I still have a question. I always see the sipes on the front tires of motorcycles pointing in the reverse direction of wheel rotation. I never see this on cars or trucks; I only see it on motorcycles. It stands to reason that the water gathered by the reversed sipes during rotation would be increased under the contact patch and possibly cause hydroplaning. The purpose of the sipes is to channel as much of the water out from under the tire and cause it to exit to the side and back from the frontal approach of the tire. So why do all the manufacturers deem it necessary to install this sipe opposite to common logic?
James W. Stevens Posted on www.cycleworld.com
A They do it because of the differences in what the front and rear tires are intended to do. Yes, they both have to help steer the bike, the front pointing the way and the rear following the front’s lead. In the wet, though, steering inputs are much less aggressive than they are in the dry. And as I explained in last month’s Service, because of their comparatively narrow, rounded shape, motorcycle tires are less prone to hydroplane than are car tires. So, instead, the most important task the rear tire must perform in the rain is to accelerate the bike (push it forward) controllably, while the most important job of the front tire is to help it brake (in essence, push it backward) controllably. Consequently, the sipes in the front tire are aimed in the opposite direction of those in the rear tire. That orientation indeed might cause the front tire to hydroplane a bit more easily any time the front brake is not in use, but as I stated earlier, such planing is much less of a problem with bike tires than it is with car tires.
Ins & outs of intervals
am wondering why there is such a big difference in valve-adjustment intervals between motorcycles and automobiles. Most of the motorcycles you test (except H-D and others with hydraulic adjusters of some sort) have frequent valve-adjustment intervals, some as often as every 7500 miles, as on the Ducati Monster. So, why don’t automobiles, many with sophisticated sohc or dohc valvetrains and high horsepower-to-displacement ratios, require their valves to be adjusted so much more infrequently, if at all?
Bob Carbon Thibodaux, Louisiana
A
There are numerous answers to that question, none of which tells the complete story; but all together, they would seem to offer a reasonable explanation of the discrepancies in recommended adjustment intervals.
Most car engines employ some sort of hydraulic device in the valvetrain that automatically maintains valve lash at zero. But for those that do not, let’s consider differences in rpm. On the vast majority of the motorcycles in question, the engines spin at higher rpm when just cruising at legal freeway speeds than most car engines ever reach. This means many more valve openings and closings per mile on the bike. If the motorcycle is a supersport, its engine has a redline that’s two or two-and-a-half times higher than a car’s, and chances are great that its rider will frequently exercise that high-rpm capability, either during a track day or when playing racer on backroads. So, the bike’s valves could, on average, open and close three or four times more per mile than would the car’s valves.
There’s also the matter of valve size. Car engines have bigger valves, which also means more valve-seat area per valve. Changes in valve clearance occur mostly due to what is called “valve recession,” which is what happens as a valve continuously hammers against its seat when closing, gradually decreasing valve clearance. Further, high-performance bike engines generally have more-radical camshafts than car engines, with proportionately higher lift and more-rapid openings and closings. So, with greater valve-seat area, combined with a lower rpm level (which translates to less-forcefUl impact upon closing), less-radical camshaft profiles and fewer open-close cycles per mile, the car valve loses-or gains-clearance much less often.
Another relevant fact is that car manufacturers are required by law to warranty their engines against anything that would affect emissions output for 100,000 miles; motorcycle manufacturers are not. Given that mandate, the car companies work tirelessly and diligently to use materials, manage combustion heat and design valvetrains that will meet that requirement with little or no maintenance.
Don’t think that motorcycle companies simply do not have the technology or wherewithal to take advantage of automotive valvetrain designs. Many bike companies also manufacture cars and have that kind of knowledge at their disposal. Honda, Suzuki and BMW all are players in the auto biz, and Yamaha has been designing and developing engines for Toyota’s GTS series for many years.
More is more-or-less less
After reading your August-issue comparison of the BMW
K1300GT and Kawasaki Concours 14, I have a question: Why does the higherrevving, lower-geared, higher-horsepower BMW get better fuel mileage than the lower-revving, taller-geared, lowerhorsepower Kawasaki? The GT’s 13pound weight advantage and 59 fewer cc don’t seem to add up to 4 mpg, given all the other stats.
Steve Tatreau Posted on www.cycleworld.com
Feedback Loop
letter the in “Boots September’s are made Service, for rotting” there was no picture of the rubber boots that deteriorated on Mr. Fritzke’s H-D Showa shocks, so I don’t know if my suggestion is dead-on. But I had a ’69 Triumph Bonneville in the early 70s that had rubber fork gaiters. The original pair rotted and split in about a year, and they weren’t very easy to replace. I found that rubbing them down with silicone kept them from rotting. After another year and a half, the second pair still looked and felt like new.
Jim Hanson Posted on www.cycleworld.com
Good idea, Jim. I don’t know if a 2002 Harley’s shock boots are made of the same material as a ’69 Triumph’s fork gaiters, but it’s worth a $5 can of silicone spray to find out. And as my friend Terry Shepherd is fond of saying, “It couldn’t hurt!” Thanks for the tip.
Even though that test was a direct comparison and the vast majority of the riding was conducted with both bikes at the same time, that was not always the case. During the two-month period in which those bikes were in our possession, testers occasionally took one bike or the other on a ride all by itself using a route that was not necessarily also traveled by the other bike. Sometimes it was just a trip to and from home, sometimes a short weekend jaunt; sometimes two-up, sometimes solo; and they no doubt rode at various speeds and levels of aggression that likely were not exactly replicated by other riders. With bikes that have the high-performance potential of these two, seemingly small differences in riding styles and routes can result in large differences in fuel consumption.
Add to this the fact that while upgrading the K1300GT from its K1200GT predecessor, BMW developed some unusually sophisticated fuel-injection technology that allows the system to monitor and regulate the mixture with exceptional quickness and accuracy.
This permits the 1300 to meet European Union EU 3 emissions standards and improve fuel mileage without negatively affecting performance. Not that the Kawasaki’s EFI is second-rate; it’s just that the K1300GT was developed more
recently than the Concours, which has gone unchanged since its introduction in 2007.
If you combine all these variables, it should be easy to see how a higher-revving bike with more horsepower could have gotten about 10-percent better fuel mileage.
Candid Cameron
explain would the like benefits/disadvantagfor someone there to es of a V-Twin with a single-pin crankshaft. I’ve worked on engines all my life, and I can see no advantage to this arrangement other than the exhaust sound-if you like that sound.
Reg Collins Noblesville, Indiana
assuming you are suggesting that a V-Twin with offset crankpins is superior to engines in which the two rods are on a single pin, such as Harley-Davidsons. In some large Japanese cruiser engines, the pins are offset to emulate the perfect primary balance provided by a 90-degree V-Twin, but the problem with this design, as I understand it, is the fatigue durability of the crank. The designer of an offset-pin crank must try first of all to place the rods as close together as possible axially to avoid the rocking-couple imbalance that arises from having the two rods operating in widely separated planes. But when the two offset pins are placed as close together as possible, the result is an awkward shape for the stresses the crank must withstand, and the result-if the crank is operated above the fairly civilized rpm of street use—is fatigue cracks originating at the fillets where the crankpins join the other parts of the crank.
When Commonwealth Racing built a roadrace bike powered by a Honda dirttrack RS750 engine with offset pins, they found it necessary to change the crank every 150 miles to prevent failures. At least two of the many people who built race versions of the Honda Ascot engine began collections of broken cranks, one of which I still have. I know of a California shop that went so far as to make a billet crank from something like 4340 steel-and it broke in the usual way.
The offset-pin V-Twin crank is a clever solution to imbalance because not every situation lends itself to the bulk of a 90degree cylinder angle (at which perfect primary balance can be achieved with just crank counterweights). Provided that such an engine doesn’t have to operate at racing rpm, it can be perfectly satisfactory.
Kevin Cameron
The car-tire controversy
fairly regular on your forum, and this car-tire-on-a-motorcycle thing seems to go on forever. Can you folks put this subject to rest? Are car tires on bikes no big deal, a good idea, sure death or what?
Paul SaintClair Asheville, North Carolina
Recall Roster
NHTSA Recall No. 09V347000 Buell XB12SS Model year: 2009 Number of units involved: 405 Problem: On certain motorcycles, the front-brake line may contact the front tire. This could cause a hole to develop in the brake line, allowing brake fluid to leak. This condition might result in an ineffective front brake and lead to a crash.
Remedy: Dealers will inspect the front-brake line, and if it is undamaged, Install a guide on the line. If the line is damaged, it will be replaced and re-routed. Owners not receiving this free remedy should contact Buell at 414/343-8400.
They are much more than no big deal, clearly not a good idea but far short of sure death. Here is the irrefutable truth, espoused by every motorcycle designer, tire technician and worthwhile engineer who ever killed a single brain cell thinking about such matters: A motorcycle will not and can not possibly have the same degree of agility, stability and maneuverability with a car tire at either end as it can with a motorcycle tire. I know, some people swear by car tires, heralding their significantly longer-wearing capabilities; but there is not one scintilla of hard evidence that supports the contention that the use of car tires on motorcycles results in no loss of safety or control. Anyone who thinks that tilting a motorcycle up on the sharp, narrow outer edge of a flatprofile automobile tire when cornering is a good idea is either poorly informed or downright delusional. □
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) Mall 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 “Contact Us” button, select “CW Service” 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.
