Track Test: Ofna Jammin' X1 CRT National Champ in a box
Words: George M. Gonzalez
CHASSIS. The CNC-machined and hard-coated aluminum chassis is 16.9 inches long—over 1 inch longer than the X1 CR buggy’s chassis. This is where the CRT gets its extra-long truck wheelbase. Sections have been milled out to reduce weight and to allow key drivetrain components to be positioned lower on the chassis. The 7075 billet-aluminum front and rear chassis braces are standard, and they’re each securely anchored to the chassis with two screws and two locknuts. The CRT features a functional, trick-looking plastic front bumper and skidplate. The 5-piece tubular bumper protects the chassis and suspension in a crash and resists “digging in” when landing off jumps nose-first. The woven-carbon-fiber servo tray and center diff and steering plates are light and rigid and look great. The steering servo is mounted lying down (to lower CG slightly), and the servo mount doubles as a mounting point for the radio tray. A radio box houses the receiver and the onboard battery pack. Separate lids secured with body clips allow you to access each item individually. A transponder mount that accommodates both personal and handout transponders is also included. DRIVETRAIN. Power is transferred from the engine by a light aluminum 3-shoe clutch. The clutch shoes have stiff gold springs, and they pivot on pins that are pressed into a small 35mm-diameter aluminum flywheel. The 13-tooth vented clutch bell meshes with a giant, 62-tooth steel spur gear and spins the center diff. The resulting final gear ratio is optimized for truck duty and provides the best overall acceleration and top speed. The 4-gear bevel diffs have hard-anodized aluminum crosspins, and their cases are sealed with rubber O-rings and paper gaskets to make them leak-proof. A bottle of 5,000WT silicone diff fluid is provided for all three diffs. Front, center and rear universal drive shafts provide full-time 4WD, and the entire drivetrain, including the wheel hubs, spins on rubber-sealed ball bearings. The CRT has a dual-disc brake system with 3mm fiberglass brake rotors and steel calipers—a departure from the X1 CR buggy’s quad brake system. According to Jammin’ Products, the fiberglass brake rotors provide smoother, more predictable braking, and they resist fading during long main events. The brakes are also less “grabby” than the quad-brake setup, and that makes it easier to adjust the truck’s flight attitude.
I tested the CRT with an OFNA/Picco P7-R Evo .21 engine and a Jammin’ Products JP-1 tuned pipe. All of the necessary accessories to attach just about any .21 to .28 non-pull-start engine are included.
The CRT has a woven-carbon-fiber radio tray, a center diff plate and a steering plate. The steering servo is laid down to lower CG slightly, but the throttle servo is mounted high on separate mounts to provide clearance for the giant steel spur gear.
The receiver and battery pack are in a sealed box. Separate compartments allow you to access the components individually, and body clips keep the lids shut. The molded-in antenna mount makes antenna routing easy.
The 7075 aluminum chassis is hard-coated for extra stiffness and machined to reduce weight. The extended chassis gives the CRT its long truggy wheelbase.
SUSPENSION AND STEERING. The CRT shares the X1 CR buggy’s C-hubs, steering knuckles and rear hub carriers, but that’s where the similarities end. Extra-long front and rear suspension arms stretch the truck’s width to over 17 inches. No wheel-hub extensions or wide offset wheels here; in fact, the suspension geometry (including front and rear roll centers) has been configured for truck racing. According to Jammin’ Products, the long-arm suspension is designed to provide more up-travel to make the truck more forgiving in the rough stuff. The CRT has the same 7075 machined-aluminum steering knuckles as the X1 CR buggy, so it uses the same T-bolt and nut hardware. This is a great feature because the steering knuckles are secured to the C-hubs with T-bolts and locknuts—no need for thread-lock. The shocks are attached to 4mm, 7075 aluminum shock towers that are much larger than the buggy’s and offer an array of shock-mounting and roll-center options for tuning. The towers have been milled out to reduce their weight and hard-coated to increase strength. The shocks look like the same threaded-body, hard-coated-aluminum units as the buggy has, but they’re new, 13mm, big-bore shocks designed specifically for the truck. If you haven’t guessed, the shocks hold more oil for increased damping. Rubber shock-seal covers are used instead of shock booties, which are known to wear out quickly. The covers have internal felt O-rings that wipe the shock shafts clean with every stroke. The shocks also have double O-ring seals and heavy-duty shock bladders, and they’re equipped with medium-soft blue springs. The suspension arms, C-hubs and rear hub carriers pivot on steel hingepins that are captured with locknuts—no E-clips. The CNC-machined 7075 aluminum arm mounts include lower front “B” blocks and 2.5-degree toe-in rear blocks, and the parts are hard-coated like the rest of the aluminum components. Adjustable swaybars (2.5mm front and 2.8mm rear) keep the CRT flat in the corners. A conventional dual-bellcrank steering system with an integrated servo-saver turns the wheels. The beveled edges on the ends of the steering drag link allow the steering-rod ends to pivot at a greater angle without binding. The steering drag link is CNC-machined 7075 aluminum and so is the servo-saver tube. Like the X1 CR buggy’s, the CRT’s suspension is completely adjustable. Camber, caster, roll center, Ackerman, toe, anti-squat, front kick-up and wheelbase can all be adjusted, and the parts and tools you need are included with the kit.
Extra-long suspension arms give the CRT its wide truggy stance. The 7075 billet-aluminum shock towers, aluminum threaded-body shocks and swaybars are standard issue. Check out the tubular bumper and body posts mounted on the shock tower—CRT exclusives.
The suspension arms pivot on captured hingepins, and 7075 billet-aluminum arm mounts are included. The kit includes 2.5-degree rear toe-in blocks and front “B” blocks, which are the hot setup.
ENGINE AND ACCESSORIES. The CRT does not include an engine, but it has many of the accessories that you need to install a non-pull-start .21 to .28 engine: a light, 3-pin flywheel, aluminum clutch shoes and springs, a clutch nut and mounting hardware are included, along with 7075-aluminum engine mounts with machined cooling fins. The CRT is equipped with a 150cc fuel tank to stretch the time between fill-ups. The tank has a cap-mounted pressure tap, a built-in stone filter and a spillway with runoff. There’s also a hard-anodized-aluminum inline fuel filter, all the necessary throttle- and brake-linkage hardware and a generous length of clear silicone fuel line. BODY, WHEELS AND TIRES. The feature-packed CRT chassis is topped off with a great-looking, narrow, Lexan racing truck body. The body is mounted low and tight on the chassis—so tight that its right side wraps around the tuned pipe. Aluminum tape is supplied to prevent the pipe from melting the body, and window masks simplify painting. The yellow nylon rear wing was designed for this truck. It’s smaller than typical buggy rear wings and looks awesome. Tires account for 75 percent of the dialing-in process, and the CRT includes excellent racing rubber: Pro-Line Crime Fighter MT tires with medium-density foam inserts plus racy-looking, yellow dish wheels with 17mm hexes.
Pro-Line Crime Fighter MT tires are standard on the CRT. The rims use 17mm hexes just like most buggies’.
BUILDING & SETUP TIPS The CRT is a pro-level kit that requires careful assembly. The kit goes together well, and the instructions are clear and concise, but be sure to take your time when you build it to ensure that everything goes together properly. The instruction manual had not been finalized when I built the truck so I had to use the X1 CR buggy manual. For this reason, I can’t provide info on particular steps, but here are some basic building tips to help you out.
DON'T FORGET THE THREAD LOCK Be certain to use thread-lock on all the machine screws that thread into metal. Put it on the screws that are secured with locknuts and the setscrews that secure the linkage stops, too. Don’t skimp on the thread-lock or you’ll be searching in the dirt for screws that vibrated loose. GREASE THE GEARS Grease the gears Instead of white grease, use Associated’s black grease or a similar moly lube on the ring and pinion gears to ensure that they work smoothly. SHIM SETUP The kit includes 0.2mm shims to set the lash between the ring and pinion gears. Install two shims on the diff outdrive closest to the ring gear and one on the opposite outdrive. This will provide a slightly tight initial gear mesh, but the mesh will smooth out after a couple of runs.
SCREW STARTER For easier screw installation in the kit’s hard plastic parts, use a tapered reamer to start the holes and allow the screws to be threaded in more easily. SMOOTH SWAYBAR Be careful not to overtighten the 3x8mm screws that secure the swaybars to the diff cases. They must be able to pivot without binding. LOCK THE CLUTCH NUT Put thread-lock on the clutch nut before you tighten the flywheel. These nuts are notorious for loosening. SORT THE SPACERS Pay close attention when you install the seals inside the shocks. Each shock requires a 1mm spacer, a 2mm spacer and two rubber O-rings. It’s way too easy to install the wrong spacers between the seals, so build carefully.
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