Service
SERVICE
Me and my Shadow
PAUL DEAN
I have a 1984 Honda VT700 Shadow that has been a great bike for many years (rides good, runs good and handles pretty decently for a cruiser). The only rub is that it doesn’t have much top end. Top speed is 75-76 mph, and on even the slightest incline I’ll lose an easy 5 mph or more until the road levels out. I’ve had it to the dealer for service and everything checks out fine. Other riders who have bikes of similar years and size say that’s about all I can expect unless I upgrade to the 1100 model, which I don’t want to do. Is there anything I can do to improve the top-end performance? MAC makes a performance exhaust system I plan to purchase, but I haven’t been able to find any performance air filters in the aftermarket. Do you know of any? My goal is to run 85-90 mph flat-out on top end. Will a better exhaust and a performance filter get me some more top speed? Jim Lang Louisville, Kentucky
A Despite what your dealer and fellow riders might say, something is wrong with your Shadow’s engine. When we tested the VT750C-the original 749cc Shadow-in 1983, it managed a top speed of 109 mph. The di splacement was then dropped to 694cc the very next year to dodge the stiff tariffs imposed on foreign imports of 700cc or larger. We didn’t test a VT700C until 1986, but when we did, we still got a top speed of 107 mph. And that was despite the engine having been slightly detuned between the ’85 and ’86 model years to deliver more bottom-end grunt. What’s more, that ’86 700 Shadow testbike ran 94 mph in the quarter-mile and would do 73 mph in third gear! So, performance-wise, your bike is a mere shadow (ouch!) of what it should be.
When a engine runs in the manner you describe (no misfires or hesitations but cannot even approach its intended top speed), the cause is usually either a loss of compression and/or a shift in the cam timing. You didn’t state how many miles are showing on the odometer, but after 23 years of use, the engine may simply be tired. Worn rings, leaky valves and stretched cam chains all could be at fault, either individually or collectively.
If your Shadow’s engine were in top running condition, a freer-breathing exhaust system and a less-restrictive airfilter element would boost top speed, but only by a few mph, not 10 or 15. Before you invest in those aftermarket components, you need to find out what is making your bike run so poorly. Otherwise, you’ll just be wasting time and money.
In case you do get the problem rectified, you should know that K&N sells an air-filter element for your ’84 VT700. It’s part number HA-1326 and has a suggested retail price of $45.
Yikes! A math lesson
Ql’m confused. In the specifications you include at the end of some of your road tests, you list the high, the low and the average fuel mileage figures, but the math doesn't make sense to me. For example, I remember one test where you said that a bike got a high of 50 mpg, a low of 40 and an average of 43. Wouldn’t the average be 45, which is halfway between 40 and 50? In another, you said that the high was 47, the low was 36 and the average was 40. Again, wouldn’t the average be 41.5, which is halfway between 36 and 47? What am I missing here? Frank Donateili New Castle, Pennsylvania As to BMW final-drive lubricant, here again the maker determines a class of lubricant that will do the job. I don’t know what that is but it will likely have a designation such as GL-4, GL-5 or GL-6. These are gear lubricants containing so-called extreme pressure additives, and it is these additives—usually chlorine and/or phosphorus compounds-that give gear oil its characteristic stink. When a hot spot forms on a gear surface, these compounds react with the hot metal to form a protective layer of metal phosphide or chloride, which has a low coefficient of friction and is sacrificed if friction is high enough to scour it away. A new layer forms repeatedly, resulting in a kind of local polishing action. The additives in GLs are usually not compatible with the needs of an engine oil, and gears don’t do very well in engine oil either, unless they are sized to carry loads with only engine oil as lubricant. This is usually the case modern motorcycle engines, and is why their gears are so large. Kevin Cameron one tank of gas is involved: You have to add up all the miles traveled during the affected tanksful and all the fuel consumed during that same period, then divide the total miles by the total gallons. A Answering those questions in detail could fill a small library, so considering the very limited space available here, I’ll only be able to surf the high points. To begin with, the engine designer has to know what purpose the finished motorcycle will be intended to serve. Will the engine go into a racebike, a sportbike, an all-around street performer, a cruiser, a touring bike or what? That is the guiding light for virtually every decision the engine designer must thereafter make. Those decisions involve important aspects of the engine such as its feel, sound, vibration, power characteristics, peak power potential, physical dimensions, packaging considerations, manufacturing cost and, in some instances, ability to use that same basic engine in other models. A flat-tire repair kit is like insurance; It’s something you should always have but hope you’ll never need to use. And if you are going to carry one along on your rides, it should be a good one. One of the nicest I’ve ever seen is this $32 kit from Aerostich (part #4674; www.aerostich.com). It contains five CO2 cartridges, an air chuck, a flexible connector, a tube of rubber cement, a tire-hole reamer, a plug installation toot, a small scraper for roughing up the area around a hole, a selection of patches and tubeless-tire “string” plugs, plus a little foam rubber sleeve that slips around the cartridges to prevent your fingers from getting frozen while installing the CO2. Alt this weighs just under a pound and is packaged in a 31/4 x 61/4 x 11/4-inch zippered nylon pouch, so it won’t tax your bike’s GVWR or take up much room in your onthe-road toolkit. purposes. But engines of a given displacement with a greater number of cylinders rev higher and generally make peak power at high rpm and less torque at lower revs, so they aren’t usually as suitable for cruisers. Inline-Fours also have “flat” crankshaft layouts that tend to produce quite a bit of secondary imbalance. which can be a significant aid to handling. And no one can dispute that VTwins sound great. With 90-degree V-Twins such as Ducati’s, that advantage is somewhat offset by the front-torear length of the engine. This forces a shorterthan-ideal swingarm and, as with V-Fours, makes it hard to get ideal weight on the front wheel. Aprilia tried to overcome those problems with 60degree V-Twins, but that angle allowed enough vibration to warrant the use of dual counterbalancers. A Let me answer your last question first. Manufacturers provide their dealers everywhere with motorcycles jetted for sea level simply because they do not know where those bikes may be ridden. Just because someone buys a motorcycle at 4500 feet doesn’t mean it won’t be ridden at lower altitudes. If an engine jetted for ideal fuel mixtures at 10,000 feet is ridden at or near sea level, it will quickly either seize its piston(s) or detonate itself to death. Conversely, if an engine jetted for sea level is ridden at 10,000 feet, it will perform poorly but at least won’t suffer any damage.
AI think you are confusing the terms “median” and “average.” The median of a list of numbers is found by putting all of them in order, from the smallest to the largest; the number in the exact middle is the median. There always will be as many numbers greater than or equal to the median in the list as there are numbers less than or equal to the median.
In your examples, you used only two numbers (the highest and lowest mileage figures), then essentially found the middle number-the median-by adding them together and dividing by two. But let’s suppose you had more mileage numbers to work with, and that over 7 refuelings, a bike got 40,
41, 42, 43, 47, 49 and 50 mpg. In that grouping, the median would be 43. Now let’s change a few numbers and say that the bike got 40, 42, 42, 43, 44, 47 and 50 mpg. The median is still 43, the number in the middle.
Another mistake people often make when trying to calculate average fuel mileage over numerous fill-ups is to add up all the averages and divide by the number of averages. If, using that last set of figures, we take that approach, we get 44 (40 + 42 + 42 + 43 + 44 + 47 + 50 = 308 - 7 = 44). And if you do the same with the first set of figures (40, 41,42, 43, 47, 49 and 50), you get 44.57. But neither of those numbers are the bike’s average fuel mileage over 7 tanks of gas; instead, each one is the average of its respective set of averages. The actual fuel mileage during that period will differ, perhaps even to a large degree.
There is only one way to determine average fuel mileage when more than
Candid Cameron
I’ve been riding since the mid-1960s and, like everybody else, have heard horror stories about oil breaking down trom heat and pressure. Can you tell us, simply, what that means? Does 40-weight oil become 10 weight or kerosene? Is the breakdown permanent? When oil is re-refined, does it come out as a lesser quality or viscosity? I ask all this because, years ago, I heard claims that with certain filters, oil could have an unlimited service life. Even now, there’s a debate on the CW online forums about BMW driveshafts and recommended oil e intervals. Fid Hawser Posted on www.cycleworld.com
Oil breakdown could have several components but the simplest is the “falling out of grade” that happens to multi-grade oils. These are oils whose viscosity index (slope of the viscosity-versus-temperature curve) has been enhanced by the addition of a percentage of “variable geometry” polymers. When cold, these effectively roll up in a ball, making little contribution to viscosity; but as the oil warms, thermal activity causes them extend progressively to become long-chain polymers that slow the natural loss of viscosity with temperature.
In olden times, skeptics could point to early breakdown of such polymers, but better ones have been developed and now even the diesel people accept multi-grade oils as valuable. The idea is this: that you choose an oil for a given engine based on its ability to support loads in the hottest places—the top ring groove and the exhaust valve guide. If the oil has adequate viscosity for those hot zones, it certainly has too much viscosity elsewhere, such as in crank bearings, the lower ring grooves, camand-tappet, etc. Ideally you’d like an oil whose viscosity was right everywhere, and multi-grades are the best approach to that.
The polymer added to make a multi-grade can be broken by rapid , such as what takes place between gears and between cams and . It can also be broken down by excessive temperature, although oil makers claim you get what you pay for here.
Incidentally, oil makers do not generally make the additives in their oils. These are supplied by specialist firms such as Paramins and Lubrizol, and are in the form of “additive packages”
¡sting of the multi-grade polymer, anti-wear, anti-foam, anticorrosion, etc. additives, all prepared to various price levels. Vehicle enthusiasts are always wanting to “do
for their engines, and this makes them /ulnerable to claims of engine life extension. My view is that the maker conducts tests to determine which oils will carry the load, and that therefore use of whichever oils are specified in the owners’ manual is wholly adequate. Those who wish to pay $32 per quart for ambitious lubricant claims are free to do so if it makes them happy. I find that ice cream-much cheaper— provides me at least equal happiness.
I can illustrate this with a simple example. Let’s say that during one tankful, you rode very conservatively at moderate speed for 250 miles and then, at a gas station located at the very beginning of your favorite backroad, the tank took exactly five gallons. That’s 50 mpg (250 = 5 = 50) on that tankful. You then flogged the bejeezus out of the bike for the entire 40 miles of that backroad before stopping at a gas station at road’s end where the tank required 1.2 gallons. That’s 33.3 mpg (40 = 1.2 = 33.3) on that tankful. If you use your method and add the two averages then divide by two, you get 41.65 (50 + 33.3 = 83.3 -52 = 41.65). But if you do the math correctly by dividing the total mileage (290) by the total fuel consumed (6.2), you get 46.77, the true average fuel consumption for those two tanks of gas.
The wheel deal
Q What’s up with the 16/4-inch wheels that are the current trend on racebikes? Prior to the mid1980s, 18or 19-inch wheels were standard fare until 16-inch wheels came along and were briefly thought to be the hot ticket. By the early 1990s, 16-inch wheels had given way to 17-inch wheels, which ever since have been the standard on sportbikes and other performance motorcycles. But now the shift appears to be toward 16!/2-inch wheels. What has happened that made the designers go first to smaller wheels, then to bigger wheels, then back to smaller wheels? Dale Bright Federal Way, Washington
A Technology constantly marches onward, often allowing what previously had been proven impractical to be made not only feasible but preferable. This is true with many aspects of motorcycle design, such as four-cylinder engines, overhead cams and four valves per cylinder. All of those were produced at one point or another in the early days of the sport, then abandoned as impractical before being resurrected years later and becoming standards of the industry.
So it has been with wheel sizes. In the 1980s, motorcycle engineers and race tuners concluded that the reduced gyroscopic effect of 16-inch wheels compared to that of 18or 19-inchersespecially on the front-helped racebikes and sportbikes to be more agile, especially when flicking into and out of fast corners and through esses.
Trouble was, 16-inch wheels had more or less been “glued onto” existing motorcycles, so tire technology, steering geometry and chassis design had not been fully developed to complement 16-
Feedback Loop
Q0n page 116 of your Service column in the December, 2006, issue, you describe the adjustment procedure for the transmission shifter pawl on a 1999 Harley-Davidson Road King (“No shift, Sherlock”). I thought I would bring to your attention that the shifter pawl is no longer adjustable on Twin Cam Harleys, which were introduced in 1999. That adjustment feature went away with the last of the Evolution Big Twin engines.
Bill McCarter Kennesaw, Georgia
A Thank you for attempting to keep me on my toes, Bill, but I’m afraid you are incorrect. Harley introduced the Twin Cam 88 engine in 1999 only on the Dyna and FL series, and they retained the same basic transmission internals—including the adjustable shifter pawl-as used with the Evolution motors. When the counterbalanced TC88B engine came along the very next year in the Softail series, it had a redesigned transmission that eliminated the adjustable shifter pawl, but the Dyna and FL models didn’t get that gearbox until 2001. So the information I gave to Mr. Manesis in that December Service reply is indeed accurate.
inch wheels. As a result, bikes with 16inch fronts in particular tended to behave unpredictably in certain situations, enough so that they soon fell out of favor. By then, 17-inch wheels had shown to be a much more reasonable compromise between stability and agility, and they quickly became the industry standard for performance bikes.
But racers in particular are perpetually dissatisfied, always tweaking here, trying something different there in hopes of gaining of a few hundredths of a second on the track. As engineers developed more-sophisticated ways of understanding precisely what motorcycle tires, suspensions and chassis do when pushed to ever-increasing limits, the matter of wheel sizes inevitably entered the picture. And the affected technologies had evolved to the point where 1614-inch wheels have demonstrated a marginal handling advantage over 17-inchers.
So far, that has just been in racing conditions. Will sportbikes follow suit? Probably. But only time will tell for sure.
Engine-eering
QI have a question concerning engine layout. Your magazine always provides statistics about motorcycle engines, but I don’t see the importance of some of it. First, once you decide on a certain displacement, there are a number of possible engine layouts. What are the advantages and disadvantages of parallel-Twin, Triple, inlineFour, etc. versus V-Twin? And once the V-Twin option has been chosen, what is the big deal between 90-degree, 60degree, 45-degree, etc.? Andy Hoover Posted on www.cycleworld.com
Generally speaking, for any given displacement, a greater number of cylinders yields more valve area, and more valve area yields more power; so the easiest way to make more power for high-performance models is to add cylinders. If the engine gets too wide, of course, either the cornering clearance will be restricted or the engine will have to sit higher in the chassis, raising the center of gravity and thereby slowing the handling. Inline-Fours currently seem to be the best compromise for performance
Tool Time
V-Fours offer four cylinders in an engine only about as wide as a Twin, but they are more complex (and therefore more expensive) and make it difficult to get sufficient weight on the front wheel for good sport/racing handling, and fitting a tuned exhaust can constitute a plumbing nightmare. Current MotoGP designs seem to be overcoming those challenges, but those are racebikes on which manufacturing costs and streetability are not concerns. InlineTriples, meanwhile, are narrower than inline-Fours, are naturally a little torquier and, with their typical 120-degree cranks, vibrate very little; but they can’t quite match Fours for sheer power, and they produce a “rocking couple” that results from their straight-across 1-2-3 or 3-2-1 firing order.
V-Twins generally do not have a performance potential equal to that of Fours or Triples, primarily because they can’t have as much valve area and are unable to rev as highly as equaldisplacement engines with more cylinders. V-Twin Ducatis have won numerous Superbike championships, but those usually came when Twins had a 33percent displacement advantage over Fours or when the manufacturers of Fours were not putting forth a full factory effort. Ninety-degree Vees do, however, have perfect primary balance that allows them to be smooth-running, and they also have the advantage of being narrower than Triples or Fours,
And 45-degree V-Twins shake so much that their most resolute proponent, Harley-Davidson, has had to either let the engines float in rubber or equip them with chain-driven counterbalancers.
This explanation barely touches the surface of engine configuration and design, but I hope you at least understand the fundamental message: All of these engine designs are valid, but none are perfect. Which is best is a matter of which gets the job done with the fewest compromises for its intended purpose.
The air up there
QI enjoy riding in the mountains of Northern Utah at elevations from 4500 to 10,000 feet. I recently purchased a 2006 Suzuki DR-Z400S dual-sport, and at 4500 feet-with the help of a speed bump-I can lift the front wheel. But in the higher elevation of the mountains, snapping the throttle open to lift the front wheel over a log, or just to shoot up a hill, causes the motor to bog. I suspect that the carburetor is jetted for sea level, and rolling the throttle open results in a fuel-to-air mixture that is too rich. The Suzuki has no fuel-to-air adjustment, and I have been told the carburetor will need to be rejetted for Utah’s higher altitude.
Is rejetting the answer or is there something more to do? My question to the manufacturer and the dealer is, what logic is there in selling a motorcycle jetted for sea level to riders living at 4500 feet or more? Eric Leonhardt
Salt Lake City, Utah
This is why carbureted engines have replaceable jets and needles. Slide/needle carbs like those used on pure off-road bikes cannot compensate for the thinner air of high altitudes, and even CV (constant-velocity) carbs such as the one on your DR-Z400S have only a limited ability to compensate. Your bike’s carb does have a fuel-mixture adjustment screw, but it only affects the mixture at idle and slightly above.
So, yes, rejetting will be necessary for your bike to run decently at higher elevations. But even if you manage to attain perfect air-fuel ratios at 10,000 feet, the engine will never perform as well as it does at 4500 feet simply because the air is so much thinner at higher altitudes than it is at lower elevations. Less air equals less power, and there’s nothing you can do about that. □
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