How to: Go big?

Hetmanski, Kevin

We install XTM Racing’s big block T-Maxx kit and 24.7 engine

One of the latest T-Maxx trends is to upgrade to a big-block engine. Many conversion kits are available, but the new big– block conversion kit from XTM is sure to be very popular because it’s the most complete. Not only do you have a choice of blue- or red-anodized parts, but the one-box kit also includes a long-wheelbase chassis, extended lower braces, engine mounts, an exhaust system and more.

We completed the kit with XTM’s new bigger-than-big “24.7” powerplant for white-knuckle rip, but the same steps would apply for a .21 engine. Here’s how to install the setup on your T-Maxx.

Bigger is better, right? That’s what the engineers at XTM think. They have just introduced a new .24 engine that is sure to get you the win in the “mine is bigger than yours” contest. It features ABC construction,

a 2-needle carb. a large heat-sink head and a compact pull-start mechanism. This big block puts out a claimed 2.6hp and 28,000 peak rpm. Item no. 146028; $139.99.

Step 1 Clean and inspect.

It’s no fun to work on a dirty truck, so before you start to bolt on new stuff, pull off your Maxx’s wheels, and hose it down with denatured alcohol or a nitrospecific car cleaner. When it’s clean, check for damaged and worn parts, and replace or repair them as you install the big-block kit.

Step 2 Disassemble. Remove the front and rear suspension assemblies, engine, header and tuned pipe, fuel tank, receiver and battery boxes, servos, lower chassis braces and transmission; you’ll be left with a bare chassis. Take time to inspect and clean all the parts you removed; look for components that are worn and need to be replaced. If you plan to add hop-ups other than the conversion kit, it’s a good idea to get those parts lined up for Installation along with the conversion components.

Step 3 Swap axles. The kit includes four universal axles that have threaded outer ends to which the wheels are attached and two center drive shafts to get power from the tranny to the diffs. Replace the stock telescoping universals with the heavy-duty XTM steel universal shafts.

To ease axle replacement, remove the Inner hinge pin that holds each lower suspension arm in place. Pull the threaded end of the stock axles from each of the four hubs; then loosen the setscrew that attaches the stock drive shaft to the diffs so you can completely remove them. Grooves in the bottom of each of the stock bulkheads allow easy access to the setscrews.

Slide the new, steel drive cups for the universals onto the differential output shafts. Put a little thread-locking compound on the threads of the setscrews that hold the new drive cups in place, install the setscrews and tighten them. Fit the threaded end of the universals Into the hubs, align the dogbone ends In the drive cups that you just attached to the diff, then reinstall the lower suspension arm.

Step 4 Radio gear and fuel tank. It’s time to install the fuel tank, steering and reverse servos, receiver and receiver box, batteries and battery box. The throttle servo originally sat In the center of the chassis just behind the front body mounts. With this conversion, it’s now mounted next to the engine, just in front of the fuel tank.

Step 5 Drive shafts, brakes and braces. Remove the stock drive shafts’ halves from the gearbox and replace them with the steel drive-shaft cups provided in the kit. Be sure to Install the brake disc on the forward drive cup, and don’t forget to use thread-locking compound on the setscrews. Next, grab the extended lower braces and install them and the original center gearbox. Be sure that you install both lower braces with the longer ends pointed toward the rear of the chassis (remember, the end with two slots in it is the rear). Make sure that the spur gear on the transmission is pointed toward the rear. too.

Step 6 Front and rear suspension assemblies.

At this stage, the front and rear suspension assemblies are still separate from the chassis’ new center section. Remove the original drive shafts’ halves that are still attached to the front and rear differentials, and install the new universals. Then, turn the chassis and hold it vertical to facilitate the installation of the rear gearbox. Line up the dangling dogbone with the drive cup previously installed on the transmission (Step 3), and, at the same time, line up the holes In the bulkheads/suspension assembly with those in the chassis. Then install the screws that hold the bulkheads to the chassis and the screws that attach the skidplates to the lower braces. Apply a dab of thread-locking compound to each screw before you install it Into the upper braces. Repeat this process to Install the front suspension assembly.

Big time!

The XTM .24 fired right up for me on the first pull, and I revved It lightly to warm it up before placing it on the ground for the first of five break-in tankfuls. When I was certain the engine was ready to go wide open, I let ‘er rip. The acceleration was impressive from the first pull of the trigger the engine has so much yank that the truck flipped over onto its lid faster than I could blink. I couldn’t believe my eyes. I actually had to work to keep the front end of the T-Maxx on the ground; the .24’s power made my Maxx accelerate like a top fueler. Top speed increased only marginally with the stock gearing in place, but the .24 engine could easily pull a taller gear for higher speeds.

Longer wheelbase gives the truck more agility over small bumps and much more stability on the big jumps. On landings, the extra weight of the big engine is a little too much for the stock springs, and the truck leans more in the turns because of the higher center of gravity. A set of Trinity blue firm Maxx springs solved the problem.

Step 7 Engine Installation. Remove the original stock clutch, flywheel and dutch bell from the Traxxas .15 engine. With the provided clutch nut, Install the flywheel on the new engine. its Important to use the tapered collet from the original Traxxas engine to Install the flywheel. The collet that came with the larger engine may not have the proper taper angle for the hole in the original flywheel. Finish by Installing the clutch and clutch bell.

Attach the new engine mounts to the engine. The heads on these big-blocks are very large, and it is hard to get an Allen wrench to prop erly seat In the screw. If you have a ball-end or an L-shaped Allen wrench, you won’t have a problem, but if you don’t have one of those tools, remove the cylinder head from the engine for better access to the screws. Don’t tighten these screws on the engine all the way because you’ll need to adjust the engine position later.

Apply another dab of thread-locking compound to the screws used to attach the engine mounts to the chassis, run them through the slots In the chassis, and thread them Into the engine mounts. Again, don’t tighten these screws completely; you’ll need them to be somewhat loose for proper engine positioning.

To align the engine with the spur gear, move the engine fore and aft to align the clutch-bell teeth with the spur-gear teeth. Tighten the upper engine-mounting screws when the clutch bell and spur gear are parallel to each other.

To adjust the gear mesh, move the engine from side to side; you want just a tick of play between the gears. When you’re happy with the mesh, tighten the lower mounting screws; recheck the mesh to check that its still set correctly and wasn’t affected by the tightening. If the mesh Is “off,” loosen the screws and try it again. When the gear mesh Is right, attach the header and pipe.

Step 8 Linkages. The throttle/brake servo linkages are Included. The brake linkage is at an extreme angle, and this may cause it to bind. The Instructions show the brake linkage mounted on the outside of the chassis and the servo pulling the brake arm. Instead, I moved the linkage to the Inside of the chassis, and the linkage now pushes the brake arm. Look at the pictures to see how I hooked it up.


Before you fire up your engine, check the throttle/brake linkages to make sure that the carb opens and closes all the way and that the brakes are set properly. If everything checks out, start the engine and begin the break-in process.

Copyright Air Age Publishing Aug 2002

Provided by ProQuest Information and Learning Company. All rights Reserved

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