We introduced you to the Honda TRX700XX in our November 2007 issue right after Honda announced it would release the big-bore sport model. With more detailed info arriving from Big Red at the end of February, we can now tell you more about this all-new ride. And in the next issue, we’ll have a full ride report on the machine Honda is calling the sport quad segment’s “King of the Hill.”
But First … The question many of us asked when we heard the news, was “Why now?” Here’s Honda’s basic reasoning on why the 700XX was given the go-ahead.
“The adult sport ATV market in the U.S. continues to mature and today can be classified in three distinct, yet overlapping segments,” says Honda. Essentially, Honda already has both the entry-level adult models (250EX/300EX) and competitive 450cc-class (450R) segments well covered. Even the 400EX can spill over into both of those categories, depending on the rider and his or her skill sets.
Honda was missing the mark in the big-bore open sport quad class. In the time it took Honda to enter this field, the Yamaha Raptor 700R has become the most popular model in the sport industry and the Can-Am DS650 has come and gone. So, in order to keep with the continued increasing expectations of riders in this segment, Honda finally decided to do something about it by offering the 700XX.
Engine Honda says the fuel-injected 686cc liquid-cooled four-stroke engine can be traced back to the Baja-proven XR650R and delivers “class-leading power.” The dry-sump engine is the largest displacement single-cylinder (102mm x 84mm) ever found in a Honda ATV powerplant. It features a five-speed gearbox with reverse.
The XR650R was proven, but even so Honda says it was not just a plug-and-play engine due to the overall weight of quads vs. dirt bikes. The XR650R powerplant weighs 88 pounds. Dry, the TRX700XX weighs more than 500 pounds or 231 pounds more than the XR.
ATV Sport
The engineers knew torque was their first priority with a heavy four-wheeled machine. They determined the stroke (+2mm) and bore (+1.4mm) had to be modified for use in an ATV. However, Honda says it abides by its own design rules. That meant it couldn’t just add a big, tall engine. Why? Because that design would ultimately hurt the 700XX’s handling because it stretched the center of gravity and raised the center of gravity of the engine too far.
For use in a quad, Honda had to reduce the engine’s overall height and size. The engineers did this by increasing the crankshaft’s stroke and a shorter connecting rod to shorten cylinder height, says Honda. Also, without an oil pan (dry-sump design) the engine can be made shorter from top to bottom, and thus produces a lower center of gravity. A gear-driven counterbalancer neutralizes engine vibration, which is very critical with a large single of this displacement.
The forged piston inside the 700 mill borrows its design from Honda’s line of CRF MX bikes. It has a slipper skirt design, with the shortest imaginable skirt, to minimize friction and free up additional power. The piston has a larger 24mm pin, and churns inside a sleeve with beefy 3.5mm “walls.” The piston also receives a cooling spritz of oil on its underside from a jet extending from the center of the case.
The 700 engine’s compression ratio is a somewhat conservative 10:1. We expect the aftermarket to look at this as an opportunity to boost stock power levels with stouter ratio pistons. Keeping the compression ratio lower was achieved because of the engine’s squat design, piston size and shape, cylinder volume and overall combustion chamber’s configuration. The pent-roof shape (shallow, peaked roof) of the combustion chamber is typical of many four-valve engines, but was used to boost horsepower and torque by producing optimal locations for the intake and exhaust valves.
Honda says the 686cc four-stroke breathes through a foam filter inside a large 7.6-liter airbox. Another difference between this mill and the dirt bike’s is the intake valve size. The 700’s 36mm intake valve is 1mm smaller for improved low-rpm flow (better torque). Again, the aftermarket will no doubt explore plus-size valves once this big boy reaches the market.
To maintain fuel efficiency, improve throttle response and ensure smooth starting, a Programmed Fuel Injection system was added. The 700 has a 3.6-gallon fuel tank. One Denso injector delivers the fuel through a 44mm throttle body. For comparison, a Yamaha Raptor 700 uses a 44mm throttle body and a Can-Am DS 450 is fitted with a 46mm unit. Controlling the EFI and ignition is a Keihin Engine Control Module (ECM).
When it comes time for the engine to expel the burnt fuel, it does so through a single header. Honda engineers shaped the header for “excellent low-end and mid-range torque.” without sacrificing top-end power. Exhaust gases flow through a low decibel stainless steel muffler.
The aluminum radiator’s core size — 28mm — matches the CRF450R’s thickness. To prevent oil from “sloshing” in the separate oil tank, Honda says the engineers added two items on the 700XX. These include an integrated wire-mesh filter in the oil hose’s connector and a custom oil return pipe.
Honda added a few other features include speed limiting the 700XX in reverse and a lower engine reduction ratio. The smaller ratio (1.087:1) allowed for a smaller diameter rear sprocket, which meant a smaller receiver assembly and lower location in the frame.
ATV Sport
Driveline Honda calls the 700XX’s centered chain drive the “most notable”innovation on the machine. Engineers were faced with the problem of having to provide optimal power delivery without affecting handling. “The centered chain drive system solves a number of issues associated with Independent Rear Suspension (IRS) that have compromised competitive designs,” says Honda.
With IRS suspensions, most people instantly think they are overly heavy and far too slow to respond to aggressive cornering, uneven terrain and sporty riding. However, Honda says IRS was an attractive choice for the 700XX because it lets all four wheels remain in contact with the ground especially in rugged terrain.
Even so, Honda’s design team looked at the traditional double A-arm IRS configurations and created something different: a compact centered shaft-drive system. The team examined an IRS system like that found in the Rincon 4x4, but ruled it out due to its hefty shaft drive and basic inefficient results for true sport handling.
ATV Sport
They determined chain drive was the way to go, but had to reconfigure how the countershaft sprocket, chain and rear sprocket functioned as a whole. This also meant the engineers had to find a new way to incorporate A-arms without interfering with the chain drive. The engineers also wanted to avoid what they termed as “tucking the tail,” which they say other IRS machines incorporate.
By relocating the drive sprocket, the team created an all-new set of triple gears and shafts. The final-drive gear mounts to the end of the countershaft in place of a drive sprocket. That gear rotates a final idle gear which interacts with and spins a final driven gear.
Confused? The driven gear connects to a shaft. That shaft extends to the quad’s centerline and has a integrated drive sprocket. Honda says this system of gears is only 33mm to the left of the big 700’s centerline. That means the chain can run smoothly in line back to the rear sprocket. Honda says its unique layout provides “ample room for the location and placement of the desired A-arms.” Thus, the drivetrain design allows for longer axle shafts which, Honda says, reduce wheel travel and ultimately improve durability and decrease unwanted friction.
By centering the chain drive, Honda engineers basically lowered the central mass. Even with a rider and a full fuel tank, the machine was built to keep everything in tight to the center line. This basically means the rider should feel in control, the quad shouldn’t feel overly tall and the feedback to the handlebars should greatly reduced.
ATV Sport
Chassis Contributing to the TRX700XX’s weight is it heavy-but-durable steel chassis. It’s fitted with a removable sub-frame.
Up front the suspension consists of a double steel A-arm design with twin shocks and dual springs, which is a Honda first. The main spring and the secondary spring (top) each are single rate. Honda said bottoming is controlled by the main spring while the top spring tackles the “small bumps.” The front end supplies 10.5 inches of suspension travel and is preload adjustable.
Honda uses aluminum on the front end for the steering knuckles, hubs and wheels.
The IRS rear has the centered chain drive system. It also features steel upper and aluminum lower A-arms, which pivot on sealed needle bearings at the frame and support aluminum knuckles via oil-less bushings. The rear uses steel hubs and 11-inch aluminum wheels.
“The steel hubs offer greater resistance to side impacts and side loads. They weigh less than an aluminum hub with the same strength characteristics,” explains Honda.
Honda said the larger diameter rear wheel lets the knuckles and hubs extend further into the wheel (due to the rear brake being located within the rear drive mechanism), which let engineers add longer A-arms and axle shafts for a larger, more stable track width.
The rear piggyback shocks, provide 9.3 inches of travel and are adjustable for preload. And like many IRS designs a rear sway bar hooks to the frame and lower A-arms and controls “excessive roll.”
Other unique features are the thickness of the rear-wheel wall and the integrated, replaceable rim scrapers. Introduced on the Foreman and Rincon quads, the scrappers are added to remove mud and debris from rear wheels.
