GS1100 vs CBX - page 3


We'd charted the two Superbikes' performances, so now it was time to investigate the hardware which made the differences. First we weighed them. With the fuel tanks brimming, the Suzuki had a 51-pound advantage at 560 pounds to the Honda's 611. Obviously, a lot of the CBX's weight is in the engine. The Honda has the weight of longer camshafts, a longer crank, two more pistons, two more rods, two more cylinders, eight extra valves, two additional carbs, a jackshaft and two more header pipes. Most of these things are probably a little lighter than comparable components in the GS1100, but six of them still weigh more than four of the Suzuki's. The CBX engine weighs 234 pounds and although no weight is available for the GS1100 engine, it shouldn't weigh more than 15 pounds over the 199-pound GS1000 engine.

Width is another drawback to a six-cylinder engine. Kawasaki's solution on the KZ1300 was narrow bores and watercooling to narrow the cylinder block. But Honda was more concerned about crankcase width and cornering clearance, so they used a short stroke (53.4mm) and a bigger bore (64.5mm) for a displacement of 1047cc. Locating the CBX's alternator and ignition triggers on the ends of the crank, would make that area prohibitively wide. Instead, Honda uses a jackshaft behind the crankshaft to drive the 350-watt alternator, run the electronic ignition's triggers and accept the starter drive. A link-plate (Hy-vo type) chain wrapped around a sprocket in the middle of the crank and tensioned by a hydraulic damper drives the jackshaft. A simple clutch on the left end of the jackshaft protects the alternator from the engine's sudden acceleration or deceleration. The jackshaft drives the clutch via a gearset. A chain behind the clutch drives the oil pump.

The GS1100's lower end looks like a beefed-up GS1000. Suzuki has started using one-piece cranks in some of their bikes this year, but the 1100 uses the more expensive built-up type which is part of the company's two-stroke heritage. Suzuki has the experience and tooling to build roller-bearing cranks, but they are changing gradually to the more popular and less expensive plain bearing type instead of converting all their bikes to them in one year. The crank in the 1075cc four is stronger and has a longer stroke (66mm vs. 64.8mm) than the GS1000's. The 230-watt alternator is mounted on the left end of the crank, and a trigger for the electronic ignition (which replaces the breaker-point type on all 1980 GS models) is on the right end. Helical gears drive the enormous 18plate clutch. The transmission is very similar to the GS1000's, even using some of the same ratios. However, the 1100's transmission pieces have a higher-nickel content (2.0 percent instead of 1.6) for improved shock absorption.

The Suzuki drives its twin-overhead camshafts with a single roller chain, tensioned by an automatic tensioner. The Honda uses a link-plate chain to drive the exhaust cam. A second link-plate chain riding on its own sprockets runs between the two cams to operate the intake cam. This design permits the use of shorter chains which are less likely to whip and have tensioning problems. Actually, each of the Honda's cams is two shafts joined in the center of the engine by an Oldham coupler.

Honda started the four-valve-per-cylinder trend in modern motorcycles, and as a showcase of technology, the CBX was destined to have 4VPC. The four-valve layout allows smaller, lighter valves for better valve control. Flow is also improved with two smaller valves instead of one larger one, and heat is more readily transferred out of the valves through increased valve seat and guide area. The 4VPC system also permits a centrally located spark plug for improved combustion.

The CBX uses two 25mm-intake valves and two 22mm-exhaust valves per cylinder. The valves are set at 31.3 degrees, have fairly long stems and ride directly against the cam lobes via buckets and adjusting shims. Lift on both sides has been decreased 0.5mm this year. The intake's valve lift is now 7.8 and the exhaust's is 7.0mm.

The GS1100 also uses a 4VPC combustion chamber design but with Suzuki's own embellishments. The valves are larger in diameter (27 and 23mm), shorter, and set at a shallower angle-22 degrees. Lift is 7.0mm all around (or possibly 6.5mm for the exhaust, U.S. Suzuki wasn't sure). However, unlike the CBX and all other DOHC Japanese engines since the CB450, the GS1100 (and the new GS750) uses short forked rockers to operate the valves - one rocker for each pair of valves. This system also employs screw-type lash adjusters, so no special tools or extra shims are needed to adjust the valves.

Besides shorter valves - which means lighter valves and stronger stems - the Suzuki system of valve operation has several attractions. The cams can be set lower in the head to reduce engine height and lower the center of gravity minutely. The shallow valve angle also means that less of the valve guide pokes into the ports to interfere with mixture flow - although it also means that the port must make a tighter turn just outside the combustion chamber.

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