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Honda TRX700XX With the introduction of the all-new 2008 TRX700XX, Honda enters the large-displacement Sport ATV market at the peak of the high-performance curve and accelerates into the red zone where no one can follow. Its electric-start, fuel-injected 686cc four-stroke engine traces its heritage to the Baja-dominating XR650R and delivers class-leading power. Just as significant, the drivetrain and suspension of the TRX700XX are state-of-the-art—and then some. Specifically, Honda has engineered a brilliant centered chain drive system that permits the use of fully Independent Rear Suspension (IRS) with more advantages than traditional IRS designs.
TRX 700XX Engine / Drivetrain The lifeblood of the 700XX is its 686cc dry-sump, liquid-cooled SOHC four-valve single-cylinder four-stroke engine. With a bore and stroke of 102mm x 84mm, it boasts the largest diameter single-cylinder that Honda has ever mass-produced. Although it is infused with the heart of the potent XR650R mill, the 700XX engine has been purpose-designed and built for the rigors of ATV duty. Given the higher weight of ATVs (compared to off-road motorcycles), torque—and lots of it—was a priority. A longer (plus 2.0mm) stroke and slightly larger (plus 1.4mm) bore accomplish this. But in keeping with Honda's philosophy of mass-centralization and a low Cg (center of gravity) to achieve optimal handling, engineers determined that a taller cylinder and engine would not do. So they shortened the overall height of the engine by creating a longer-throw crankpin and a correspondingly shorter, carburized connecting rod to shorten cylinder height. The connecting rod is affixed to a ball-bearing crankshaft. Smooth, all-day riding comfort was assured with the fitment of a gear-driven counterbalancer to neutralize engine vibration. Like Honda's renowned CRF® motocrossers, the XX piston features a slipper skirt design and it strokes through a centrifugally forged, 3.5mm-thick steel sleeve. A forged piston was used to handle the increased mechanical and thermal loads, and it also benefits from an underside shower of cooling oil shot from a jet that protrudes into the center of the engine case. Compression is 10:1 and the high-tech slug is fitted with a larger 24mm piston pin. The combustion chamber utilizes a pentroof shape and is fired by a single, centered spark plug. The engine inhales through a foam air filter fitted in a 7.6-liter airbox. Intake valve size is 1mm smaller than those used in the XR (36 vs 37) for better low-rpm flow—and therefore torque—while the exhaust valve diameter remains unchanged at 32mm. The Programmed Fuel Injection (PGM-FI) system draws fuel from a 3.6-gallon blow-molded, multi-layer fuel tank and delivers it via a single Denso injector through a 44mm throttle body. A Keihin Engine Control Module (ECM) manages both the fuel injection and the transistorized ignition. The engine exhales through a single long-tube header tuned for excellent low-end and mid-range torque without sacrificing top-end power. Gases are expelled through a muffler constructed of 128-grade stainless steel. | | | |
TRX 700XX Engine / Drivetrain - Continued | Honda TRX 700XX dry-sump design eliminates an engine oil pan, which contributes to a shorter engine height and consequently a lower center of gravity. Also, the oil tank, coolant overflow, and fuel filter are positioned low on the frame for additional reduction in the center of gravity. | Coolant is routed through an aluminum radiator with a 28mm-thick core—the same core size as a CRF450R motocrosser. A special wire-mesh filter in the oil hose connector and a custom bend of the oil return pipe protects the oil from sloshing and aeration in its separate brazed aluminum tank. This dry-sump design eliminates the oil pan, which contributes to a shorter engine height and consequently a lower center of gravity. Several enhancements are made to the engine to simplify its operation and enhance durability. An automatic decompression system is activated whenever the electric starter is engaged. The starter-motor housing is incorporated into the engine crankcase casting and a disc-type torque limiter minimizes shock to the starter mechanism. Power is channeled through a five-speed gearbox with Reverse and is transmitted to the rear wheels via an ingenious centered chain drive system. Conceived with the goal of maximizing the architecture of the long A-armed, double-wishbone independent rear suspension, a row of final gears located after the countershaft positions the drive sprocket just 33mm left of the 700XX's centerline. The proprietary design allows the chain and rear sprocket to be placed virtually in the center of the rear of the ATV. This produces numerous benefits, including the use of longer A-arms and axle shafts. Longer A-arms minimize wheel camber changes as the suspension travels up and down—a handling benefit—and longer axle shafts mean that CV joints operate at less extreme angles, benefiting power efficiency and long-term durability. A further benefit of the design is simplified maintenance. | | | | TRX 700XX rear spocket (left) & rear brake rotor (right) are each located 33mm from the centerline, which is virtually in the center of the rear of the ATV | TRX 700XX ulitizes long rear A-arms & equal length axle shafts to minimize wheel chamber changes as the suspension travels up and down | | Honda TRX 700XX has 10.2" of ground clearance | Two more features of the gearbox and final drive are worth noting. First, top speed in Reverse gear is controlled by monitoring both actual speed and crankshaft speed. When vehicle speed is no less than 12 mph and the engine speed is no less than 3050 rpm (equivalent to 12 mph), fuel delivery to the injector is restricted. The second noteworthy aspect of the gearbox is the engine reduction ratio at the drive sprocket: 1.087:1. This was done to permit the fitment of a smaller-diameter rear sprocket, which in turn allows the sprocket receiver assembly to be located lower on the frame. In addition to lowering the center of gravity, the smaller diameter of the sprocket and its assembly also improve ground clearance. TRX 700XX Chassis / Suspension | | The Honda TRX 700XX frame is constructed of steel with a removable sub-frame | The frame of the TRX700XX is constructed of steel with a removable sub-frame; each is extremely durable and strong. Independent double-wishbone front suspension uses steel A-arms and premium shock absorbers featuring two single-rate springs per side. This application of dual springs, a first for Honda, separates the function of each. Both the main spring and the short top spring (second spring) are single rate. Bottoming resistance is provided by the heavier main spring and the top spring adds compliance over small bumps. Together, they achieve what a progressive-rate single spring could have accomplished, but in a lighter, more compact package that takes full advantage of the 10.5 inches of useable suspension travel. Front preload is adjusted with screw-type adjusters. The A-arms are attached to aluminum steering knuckles, which in turn bolt up to aluminum hubs and 10-inch diameter aluminum wheels fitted with 21x7R-10 Dunlop radials. | | | | The TRX 700XX front suspension provides 10.5" of suspension travel with two single-rate preload adjustable shocks | The TRX700XX has 9.3" of rear suspension travel with preload adjustable piggy back reservoirs shocks | | | The TRX 700XX has Dual hydraulic 174 mm discs up front and a single 200mm disc in the rear | The aforementioned independent double-wishbone rear suspension, made possible by the innovative centered chain drive system, features steel upper and aluminum lower A-arms. The upper and lower A-arms pivot on sealed needle bearings at the frame and support aluminum knuckles via oil-less bushings. The knuckles attach to steel hubs, and the 11-inch-diameter aluminum wheels sport 22x9R-11 Dunlop radials. The reason for steel hubs: greater resistance to side impacts and side loads. These steel hubs weigh less than an aluminum hub with the same strength characteristics. A non-adjustable rear sway bar attached to the frame and lower A-arms controls excessive roll without compromising the independent action of the IRS. Piggyback reservoir shocks provide 9.3 inches of fully usable travel and feature screw-type preload adjusters. Braking action is supplied by a hydraulic single piston squeezing a 200mm disc. The rear brake assembly is mounted on the rear sprocket receiver and is situated 33mm right of the 700XX's centerline—symmetrically opposed to the location of the sprocket/chain assembly to facilitate equal-length A-arms and drive shafts. | | | | The TRX 700XX utilizes large 11"diamater Aluminum rear wheels to allow the knuckles and hubs to reach farther into the wheel cavity, and to keep the wheel cavity clean of mud & debris, a rim scraper is mounted on the inside of the wheel | An interesting outgrowth of Honda's goal to fit the longest A-arms and axle shafts possible is the use of special 11-inch-diameter rear wheels (larger than competitive designs). The larger-diameter wheels allow the knuckles and hubs to reach farther into the wheel cavity, which effectively extends the A-arms and axle shafts to the perimeter of the 700XX's track width. To maintain strength and light weight, the thickness of the rear-wheel wall varies as it extends from the center plate to the outer ring of the wheel—another Honda ATV first. And here's another: the fitment of replaceable rim scrapers to remove mud and debris from rear wheels, a feature pioneered on Honda's popular Foreman and Rincon series. TRX 700XX Body | | The Honda TRX 700XX has an unique front fender design with a radiator screen and cowl-intergrated dual 30-watt bulb headlights | The TRX700XX shows off its high-performance capabilities with aggressive sports styling. A polyethylene push bar, polypropylene rear A-arm protectors and high-impact urethane frame and engine-case protectors are tough, lightweight and replaceable. A cowl-integrated headlight with dual 30-watt bulbs provides superb lighting and a highly visible LED brakelight is the most common view competitive riders will have of the new TRX700XX. With Honda's legendary fit and finish, coupled with patented innovations such as center chain drive, plus handling and engine performance unrivaled in the class, the TRX700XX recalibrates the standard by which all other sport ATVs are measured. ATVriders.com TRX 700XX Info Update: | I just returned from a trip to the Dumont Dunes in California to test ride the Honda TRX 700XX in rocks, water, and sand, so a full review, photos, and videos will be released in the very near future. Harlen Foley
Editor ARTICLE TAKEN FROM ATVRIDERS.COM |
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