Yokomo MR-4BC Super Dogfighter 2 Special

Radio Control Car Action, Apr 2004 by Reyes, Lito

ROLLIN WITH THE BIG DOG

FOR THE PAST FEW YEARS, YOKOMO'S ON-ROAD PROGRAM HAS FLOURISHED with new releases that include the shaft-driven MR-4 TC, extensions to the popular GT-4 line and even an updated 1/12-scale pan car. Meanwhile, Yokomo's sole off-road car, the MR-4BC Dogfighter 2, originally released in 2000, has waited patiently for an update. A "Special" kit appeared a couple of years ago and gave the BC a longer wheelbase for better bump handling and stability, but all has been quiet since.

All that has changed with the release of the MR-4BC Super Dogfighter 2 Special, which adds a graphite chassis and shock towers, titanium turnbuckles, threaded shocks and a host of other goodies to bring the BC up to "anytime, anywhere" competitive trim. Just look at the 2003 IFMAR 4WD Off-Road Worlds for proof: Billy Easton only had about two weeks of wheel time with the new Yoke, but he still managed to put it in the A-main!

KIT FEATURES

CHASSIS. The molded-graphite tub chassis is similar to the original's molded-composite chassis. Changes include certain features taken from the "Pro" version of the MR4-TC-in particular, the lowered motor-mount area that Yokomo's optional motor heat sink can be dropped right into. Battery cutouts along the chassis' right side drop the cells closer to the ground for a lower CG. A sheet of adhesive-backed clear plastic, along with a cutout template, is included to cover the exposed battery and motor cutouts underneath the chassis.

A composite upper-deck brace is used in place of the nylon "backbone" that was on the original car. Though this leaves the drive train exposed to dirt and debris, it makes the tub chassis much stiffer than it was in the BC's previous incarnation. The upper brace has a couple of mounting locations along the center to fine-tune the amount of stiffness it provides.

Batteries can be mounted with the included graphite battery retainer, but the instructions show how to install them more securely with strapping tape.

DRIVE TRAIN. An efficient and durable dual-belt drive system powers the BC. As expected in a Pro-level car, ball bearings are used throughout. The front differential has plastic outdrives to reduce weight and blue-anodized aluminum rings to prevent the outdrives from spreading under hard acceleration. Steel outdrives are used in the rear differential where more strength and durability are required.

The front belt rides on a center one-way bearing from the spur layshaft. This one-way gives the benefit of increased off-power steering (as provided by a front-mounted one-way) while the front end retains its adjustable differential action. All four corners feature steel universal drive shafts. The new steering blocks use oversize bearings that can handle more loads than the original BC's parts could. A ball-bearing belt guide is built into the motor mount. All in all, the BC's drive train is up to Yokomo's usual high standard of low friction and efficiency.

A cast-aluminum motor mount is also included and is supported by both the chassis tub and the upper deck with screws to prevent it from shifting in the rough stuff. An 84-tooth spur gear and lightweight 2o-tooth pinion are included.

SUSPENSION AND STEERING. Hard-anodized aluminum shocks grace the BC's corners. The bodies are threaded for precise preload adjustments and have dual 0-ring seals on the shaft end and a single 0-ring seal on the cap end. A hole in the cap makes shock bleeding easy. Inside the shocks, a foam ring acts as a volume-compensation buffer when the shaft slides in and out of the body. The shock shafts are all titanium-nitride-coated stainless steel with a bright, smooth finish to help with consistent shock action. Like the tub chassis, the new shock towers are made from molded graphite.

The front A-arms ride on stainless-steel hinge pins and house the steering upright/steering arm assemblies, while the rear A-arms are mounted to a rear bulkhead that allows for adjustable wheelbase. The hinge pins are secured without E-clips; instead, they're held by retaining screws or bulkhead caps.

Steering is handled by a traditional dual-bellcrank design riding on ball bearings. An adjustable servo-saver is built in, and the aluminum posts and servo-saver parts are all anodized in blue to match the rest of BC's aluminum hardware. All the tie rods, including the camber links, steering links and bellcrank drag link are Lunsford titanium units-light and very hard to break. A Lunsford turnbuckle wrench is also included.

BODY, WHEELS AND TIRES. The BC's body is a sleek piece that tightly conforms to the tub chassis to help keep dirt out. Velcro strips hold it to the tub chassis, and nylon wing mounts hold the rear wing to the rear shock tower.

The stock tires are Yokomo's own hot Laps with a low-profile mini-pin "fuzzy" design. White one-piece dish wheels adorn each corner. The wheels aren't mounted on the hubs with screws, as in the original BC, but are now keyed to the hubs with pegs molded into each wheel; this saves some rotating weight.