Technical Innovations
Honda four-stroke engine
 Honda claims its expertise in Formula One racing enabled it to produce a 96-mm (3.8-in) diameter piston that is 33.6 mm (1.3 in) high and has a mass of only 261 g (9.2 oz). |
The power and weight advantages of two-stroke engines in applications where those factors are significant have long meant that two-stroke engines were preferred for small motorcycles, scooters, and personal watercraft. But tightening exhaust emissions requirements have encouraged renewed interest in developing four-stroke engines for such applications.
Along the way toward building cleaner engines, some advantages have been realized for four-stroke engines. Off-road motocross racing places an absolute premium on the power-to-weight ratio of the motorcycle. More power means better acceleration, and lighter weight makes the bike easier to ride while also contributing to quicker take-off.
A normally-aspirated four-stroke engine is unlikely to ever match the power output of a similarly-sized two-stroke, but race-sanctioning bodies apply equivalency formulas that let bigger four-strokes race against smaller two-strokes. The leading class of motocross (and supercross, its indoor variant) is the 250-cm3 category. Organizers let 450-cm3 four-strokes race against the 250-cm3 two-strokes in this class, and Yamaha recently has had success with its YZ426F four-stroke motocrosser.
The discovery, upon the re-introduction of four-strokes to motocross racing, was that while the power was comparable, the power delivery of the four-stroke bikes is easier for riders to manage, giving them an edge over their two-stroke-mounted competitors.
 Honda has packed 449 cm3 of four-stroke power into an engine that has a mass of only 29 kg (64.5 lb) but that produces 41 kW (55 hp). The needle-bearing connecting rod follows two-stroke practice, reducing the need for oil in the crankcase. |
Honda has responded with the CRF450R, an off-road race bike that employs a 449-cm3 four-stoke engine to compete against smaller bikes. Power is rated at 41 kW (55 hp) at 9000 rpm and 49 N•m (36 lb•ft) at 7000 rpm, from a bore and stroke of 96 x 62 mm (3.8 x 2.4 in). The compression ratio is 11.5:1, and redline is 11,200 rpm.
A program of extreme attention to weight has produced a motorcycle with a claimed dry mass of 102 kg (225 lb) (claimed motorcycle dry masses are notoriously optimistic), compared to 97 kg (213 lb) for Honda's benchmark CR250R two-stroke racer.
The CRF450R's single-cylinder and single-overhead cam engine has a mass of only 29 kg (64.5 lb). Honda claims that while the CRF450R's frame is not interchangeable with that of the CR250R because of different engine mounting and clearance requirements, the two bikes are otherwise virtually identical. The CRF's frame is only 0.2 kg (0.5 lb) heavier than the CR's; therefore, the CRF450R's 449-cm3 four-stroke engine has a mass of only about 5.4 kg (12 lb) more than a 250-cm3 two-stroke.
Honda achieved that weight through the application of racing technology and by not employing technology that could add weight. Yamaha's YZ426F, in comparison, features a double-overhead cam, five-valve design. Honda opted for a single cam head with four valves.
The 36-mm (1.4-in) intake valves are titanium, with a mass of only 24.8 g (0.87 oz) each, a savings of 15.2 g (0.54 oz) compared to steel valves. The camshaft acts directly on the intake valves, but opens the 31-mm (1.2-in) steel exhaust valves through a forked, low-friction roller rocker arm. The rocker has roller bearings at its tip, enabling Honda to reduce its size because of reduced strain on the rocker. The system has a mass of 377 g (13.3 oz) less than a comparable DOHC arrangement, according to Honda.
The 96-mm (3.8-in) diameter piston is only 33.6 mm (1.3 in) tall. It looks like a disk with wrist pin bosses. The disk is wrapped by two rings instead of the usual three. A single compression ring and an oil-control ring are sufficient for a racing-only engine. The 261-g (9.2-oz) piston is 114 g (4.0 oz) lighter than a traditional piston with full skirts instead of the CRF450R's mini-skirted piston. The cylinder is Nikasil lined for reduced friction, contributing to cooler running and extended engine life.
 The single-overhead-cam arrangement—Honda calls it "Unicam"—is smaller and lighter than a comparable double-overhead-cam configuration, according to the company. |
Oil control is a less significant problem for the CRF than on most four-stroke engines because it employs needle bearings for the crankshaft end of the connecting rod. Most engines use plain bearings that require more oil than needle bearings so there is more oil in the crankcase. The CRF has a reduced oil supply in the crankcase to cut friction losses from the crankshaft and rod churning through oil.
The engine and five-speed transmission have separate oil supplies, which is unusual for a motorcycle, to keep clutch and transmission material contamination from reaching the engine and provide the clutch with a cooler supply of oil.
Kickstarting a stalled, large-displacement, one-cylinder engine is a challenge welcomed by few riders, least of all those who may have just crashed during a race and want to remount and continue as quickly as possible. Honda has built in an automatic compression release that makes starting easier. The kickstarter is also designed so it works in any gear, again saving riders time when they hope to return to the fray.
The engine's flat-slide carburetor features ball bearing on the slide, reducing throttle pull resistance so the rider's wrist doesn't get as tired during races. Dual radiators dissipate heat more effectively than a single unit, and a titanium header pipe trims weight from the exhaust system.
- Dan Carney
Improved surface finishes from Makino
 Makino's EDNC43S die sinker EDM machines uses High-Quality Surface Finishes technology, reducing or eliminating the need for surface polishing. |
The EDNC43S die sinker EDM uses patented "additive technology" from Makino to produce High-Quality Surface Finishes (HQSF). HQSF is a machining method that combines micro-discharge pulse control, high-response servo technology, and Makino's powdered additive for the machining of ribs and other hard-to-polish shapes, such as grilles.
Mixing the additive with a dielectric fluid adds to enhanced electrical conductivity for more consistent discharging. The process eliminates secondary discharges that waste energy and allow increased efficiency of the sparks for an improved surface finish, according to the company. Equalized distribution of the additive in the dielectric fluid is realized partly due to the low specific gravity of the additive, a combination of copper, high-grade graphite, and medium grade graphite. Makino claims that flushing is not necessary to achieve even additive distribution on sidewall areas or bottom surfaces. The technology also allows the use of a single-dielectric system, requiring less space and maintenance than a dual-dielectric system.
The EDNC43S is one of Makino's S-series models developed to maintain surface integrity by reducing polishing times and increasing the life of a mold. The bed of the machine is a heavily ribbed, single-piece casting that incorporates anti-friction linear guides for improved rigidity. A drop-tank design allows for easy set-ups and flexible operation as well as lower mechanical stress during orbiting. The machine has a 500 x 700-mm (19.6 x 27.5-in) fixed table with a 1000-kg (2200-lb) maximum table load and a 10-m/min (32.8 ft/min) jump cycle. Makino quotes machining accuracies to be ±0.001 mm (0.00004 in).
Single Page Programming allows for automatic programming with a minimum amount of operator inputs. The single screen menu displays prompts and questions, then the system chooses the correct power supply settings for the operator. Model Plan Programming allows experienced operators to have complete control over the EDM process. It enables jumps to be modified, or it can create a cleaning jump cycle, change orbiting speeds, or control servo speeds. The system allows less experienced operators to choose a variety of automatic routines for simple 2- or 3-D orbits, automatic positioning, and measuring. Blueprint data input screens on the CRT allow all canned cycles to be adjusted for any situation.
- Jean L. Broge
