Service
SERVICE
The Life of a motorcycle
I'd like to get a lot more information on your “Special Delivery” article in your September, 1986, issue.
In particular, I was struck by the statement that motorcycle messengers average about 40,000 miles a year. Do the bikes go this long without overhaul? How long will they go before overhaul?
I’m very interested in the projected life of a motorcycle engine. Where I live, if someone puts over 10,000 miles on a bike, big or small, they consider it worn out, and this is reflected in the resale price.
Steve A. Kay Anderson, South Carolina
We can 7 say in general how long a given motorcycle will last, but we can offer one example that should put the 10,000mile folklore to rest. Eric Malmquist, a motorcycle messenger and friend of the CYCLE WORLD staff, currently has 69,000 miles on his 1983 GPz550, without any major engine repairs. Eric, whose livelihood depends on his motorcycle, takes better care of his bike than do most people: He religiously changes oil and filter every 2000 miles in the summer, 3000 in the winter. Given his maintenance schedule, Eric would be very disappointed in any bike that failed to cover 40,000 miles without an overhaul.
Keep in mind, though, that engine life may be a function of both mileage and time. For example, standard aircraft practice is to require rebuilds after every so many hours of actual operation, or after so many years since the last rebuild, whichever comes first. That's because many engine components, such as seals and gaskets, may deteriorate with time as well as with miles. So if you rack up miles at a tenth the pace of a messenger, your bike may not carry you as far.
Last of the 350 Fours
I don’t know where else to turn. I acquired a CB350F last year, and have been slowly modifying it to make it look and go faster than what it was (a $50 whim). The only real problem is finding a cam. Andrews, the only company I got a reply from, sent me a poster and a pamphlet on cams for giant drag bikes. Am I wasting my time? My 350 Four isn't much, but it seems somebody should have a cam for it. Where do I turn to now?
Rich Chisock Erie, Pennsylvania
Hot-rod parts for 12-year-old motorcycles can be difficult to come by, but we could make one suggestion for improving the performance of your 350F: Honda already hopped up this motor a long time ago by turning it into the much quicker 400F. Parts from the 400, including the cam, may interchange. Indeed, it ma y be possible to find a complete 400F engine in a salvage yard and simply do an engine swap.
Exhaust music
Lotsa talk lately about the soulfulness of an engine’s sound. It is indeed a primordial aspect of the personality of a bike. Thus my query: Given identical bore and stroke, inlet and exhaust paraphernalia (from airbox to silencers), and the same rpm, would not a VFour, a flat-Four, a square-Four and an inline-Four all make exactly the same sound?
Second, if we were to take an inline-Four of 1 OOOcc and cut it in half (or rather build a 500cc parallel-Twin, as we still need the
1 OOOcc Four for sound-comparison purposes), and spin that Twin at twice the 1 OOOcc rpm (say, 4000 rpm vs. 2000 rpm), would we not again produce the same sound, as the number of explosions happening in identical environments would be equal?
In practice, I believe that I am wrong, as the sound of a Twin is quite easily distinguished from that of a Four. In theory, though, I fail to see where I err.
Germain Laberge Beauharnois, P.Q., Canada
Several characteristics (other than silencer design) influence engine sound. Most important are the actual cylinder pressure at the point of exhaust-valve opening, the rate at which the exhaust port is exposed, and the timing of the exhaust pulses from various cylinders. In your first example case, with the various Fours, these first two factors would be the same for all your hypothetical engines. And because inline-Fours, square-Fours and flat-Fours all share the same even firing order, these three engine types could all sound alike if given equivalent exhaust plumbing and silencing. Most common V-Fours, however, don 7 have the same evenly spaced firing order as these other engines do, and would indeed have a distinctive sound.
And there is a marked difference between a 500cc Twin turning 4000 rpm and a 1 OOOcc Four turning 2000cc rpm. For the Twin, there would be one 250cc cylinder firing every .015 second; for the Four there would also be one 250cc cylinder firing every .015 second. But the valve opening rate of the Four will be half that of the Twin, and the Four in this case should be the engine with the more bass voice (assuming equal exhaust systems, say a 2-into-2 versus a 4-into4). Also, the two engines would require different throttle settings to maintain these speeds, and cylinder pressures will almost certainly not be equivalent. With those differences, there will be no problems distinguishing the Twin from the Four.
The latest Vision
I wish to install the carburetor from a 1983 Yamaha Vision onto a 1982 Vision. What are the ramifications involved in such a swap?
As you probably know, the 1982 Vision had a stumble in its acceleration due to poor carburetor design. This malfunction was remedied on the 1983 Visions due to various modifications, and I would really like to incorporate this improvement onto my 1982. By the way, I was fortunate enough to come by a 1983 Vision with a damaged engine very cheaply, hence my ability to modify my 1982.
W. Campbell Dorval, Quebec, Canada
This swap will work as long as you change to the 1983 airbox along with the 1983 carburetor. The redesigned airbox complemented the recalibrated carburetor, but the 1982 and 1983 Vision engines otherwise were similar
Seca 900 problems
I own a 1983 Seca 900 and have several problems I’d like your opinion on:
1 ) At high speeds (above 90 mph) the bike develops a weave that gets worse as speed increases.
2) The engine runs terribly when cold (sometimes) but seems fine when fully warm.
3) Ever since I replaced the stock brake pads with Ferodo organic pads, the brakes squeal and sometimes vibrate at low speeds.
4) The brakes constantly need bleeding for best performance.
5) The forks are very soft and bottom nearly every time I brake. However, the forks are quite stiff over small bumps.
What can I do about any of these?
Rick Jones Cerritos, California
High-speed weave was a problem with some 1983 Yamaha Seca 900s, even though our test bike tracked straight if its rear suspension was set on minimum damping. The flaw was at least partially attributable to the machine's handlebar fairing; later models (the 900 Seca is still sold in Europe) came with a small, framemounted quarter-fairing. Unfortunately, short of making all the updates Yamaha incorporated in later Secas, there may be no complete fix for your bike's weave. We'd suggest making sure your bike's steering head bearings are adjusted to Yamaha specs, and checking that its tires are both balanced carefully and have no significant run-out. Also, high speed weave is very sensitive to tire wear and brand; if your rear tire is worn fairly flat in the center, it may be a large part of the probel m. And while we don't know if new tires alone will cure the weave, aftermarket radiais have been touted as improving high-speed stability; perhaps, and only perhaps, Pirelli P7s or Dunlop K700s would help.
Poor running when cold is due to lean, emissions-redueing jetting. However, since your Seca runs well warm, we wouldn 7 suggest altering the regular carburetor circuits; just make sure the choke or enriehener circuit is completely engaged at start-up.
Brake squeal as you describe it is a high-frequency vibration of the pad and disc, caused bv stick/slip behavior between the two. There are a few commercially available damping compounds you can apply to the back of the pad that may reduce squeal.
If your brakes continually need bleeding, it could be because of a leak in the system. It also could be created by air pockets that get trapped in high spots in the system and don 7 self bleed during normal operation; there are two of these created by the Seca 's ineffective anti-dive system. Simply removing the anti-dive lines (you may need shorter banjo bolts going into the calipers for this change) would surely improve brake feel.
Finally, the Seca 's fork suffers from overly soft springs combined with too much preload. Stiffer springs lightly preloaded and run with zero air-pressure would improve fork performance; such springs are available from Progressi ve Suspension (11129 G A venue, Hesperia, CA 92345; [619] 9484012) or ATK/Leitner Corp. (723 Laguna Canyon Rd., Laguna Beach, Calif. 92651;[714] 497-7525). In addition, the Seca's axle-clamping .VRStem can easily bind the front fork, pulling the bottom of the fork legs together. A custom-made axle spacer may be required to prevent this from happening.
More Seca advice
I’m 15 years old and presently ride a Husky 175. For my first streetbike I am buying a leftover 1983 Yamaha Seca 400. I plan on using this bike for transportation to and from work, for sport-riding, and some light touring.
I would like to mount a 2-into-1 exhaust system on this bike. I know there will be a top-end power increase, but would there be a loss in the low-end and mid-range where the bike will spend most of its time? Also, would the addition of a barmounted fairing such as a Tracy Streetfighter cause any handling problems such as front-end lift?
Mark Sommer Pittsburgh, Pennsylvania
There's no guarantee that an aftermarket 2-into-1 exhaust will give a Seca 400 a big power increase anyplace. The Seca uses a 180-crankshaft whose uneven firing order isn 7 ideal for a 2-into-1 pipe, and it's quite possible that a pipe change (in this case) will result in less power, more noise, and rougher running unless the the carburetor is recalibrated; we'd be hesitant to make the change unless we knew someone who had achieved satisfactory results with a particular pipe.
A handlebar fairing shouldn 7 cause any particular handling problems at the speeds possible on a 400; on a few weave-prone bikes, handlebar fairings can worsen the tendency to weave, generally at speeds well above the national limit.
K&N safety
I was wondering if changing my stock air filter on a 700 Honda Interceptor to a K&N will hurt my bike. I left the airbox lid on. My friend says it will cause me to burn my pistons. Is this true? I made no other changes, just the air filter.
Rick Caywood
Long Beach, California The simple change of air filters should have no ill effects Anything that reduces the flow restriction upstream of the carbs will tend to make carburetion leaner; and will certainly cause poor running, if not burnt pistons, if you don 7 rejet. The difference in flow between the different filters, however is small compared to the restriction imposed by the airbox, so the filter change by itself is rarely a problem. If you had removed the airbox lid. though, you almost certainly would have had to change the jetting as well.
OW-NSR drag race
Okay, so we know that, with the right gearing, Eddie Lawson's OW or Freddie Spencer's NSR can do over 200 mph. But just out of curiosity and for comparison, how fast do you think they can cover the quarter-mile?
Kurt Phillips Mission Viejo, California
Both of those GP bikes make about 150 horsepower (at the rear wheel'.), and both weigh about 260 pounds. Simply based on power-to-weight ratio (with a 160-pound rider aboard), they should run well under 9 seconds in the quarter, at terminal speeds well above 150 mph. But as we've recently learned the hard way, there's a lot more to a fast quarter-mile than a power-to-weight ratio; and because these machines have short, approximately 55-inch wheelbases and no wheel ie bars, we suspect that simpl y not looping them would take your full attention. Since neither bike is likely, then, to tolerate full throttle during much of a quarter-mile run, they wouldn 7 be nearly as quick as their statistics indicate. 0
