Honda took the sport ATV market by storm in 1998 when they released the TRX400EX. Eager to prove just how capable of a machine it could be, Honda sent it to race in the Baja 1000 where it won! Outside of a few styling updates and the occasional feature update, like adding reverse in 2005 (a few years too late), very few changes came to the machine. Over the years it developed an incredible reputation for being very reliable, easy to handle, and a great platform to build from. This is why there are so many of them out there. We breathed new life into ours by giving it everything it needed to hit the trails again.


Cutting straight to the heart of our build, we first restored the powerplant with a QA Parts Cylinder and Piston Kit. This OEM replacement kit fits like stock and brings back the original muscle Honda intended with fresh gaskets, rings, piston and cylinder, and everything else needed—including a new sparkplug.

Already well known for its great low-end grunt, we wanted to refine the engine’s power output by adding a Hot Cams Stage 1 Camshaft Kit. This kit uses the stock valve, springs, and rockers, and significantly increases the top end power band without compromising low-end grunt.

Our original TRX clutch was worn out, and we chose the Tusk Competition Clutch kit to replace it. The parts meet OEM specifications for a perfect fit; and instead of cork-based friction plates, Tusk uses an Aramid fiber for superior heat and wear resistance. They won’t distort under heavy, heated use.

Tusk Competition Clutch Kit on the Honda TRX400EX

We improved the machine’s breathing with the Pro X Foam Air Filter and the Lexx MXE slip-on silencer. The air filter is a little thicker than stock but still allows freer air flow while providing a higher level of filtration. The silencer is fully tunable and rebuildable. You can also pick up a spark arrestor and trail tip, which will help control sound output on the trail as well as meet Forest Service regulations. However, to maximize the performance available in adding the silencer, you will want to adjust your carburetor for altitude. The increased performance will be well worth it, and Rocky Mountain offers a full line of premium jet kits for your machine.


Our TRX needed protection from the trail hazards we encounter, so we started at the front. The Tusk Comp Series Aluminum Front Bumper did the trick, keeping important front end components protected in a stylish, chrome finish. Easy to install, this sturdy addition is also perfect for those times you need to lift or pull the front end.

For some peace of mind in rocky terrain, we installed a set of Ricochet A-Arm Guards. The 1/8 inch, precision-bent aluminum protects the TRX’s suspension components from damage during aggressive rides.

Ricochet A-Arm Guards on the Honda TRX400EX

To prevent hanging up on rocks and stumps, we installed the Ricochet Full-Chassis Skid Plate. This durable aluminum skid plate provides front-to-back protection for the bottom of your machine.

Usually the lowest part of the quad, swing arms are especially vulnerable to rocks, stumps, and anything else on the trail that would damage them. We added Ricochet Swing Arm guards, which also help protect our sprocket and rear disk from damage on the trail.

Next, we installed the Tusk Foot Peg Nerf Bars with Heel Guards. The 1 3/8 inch alloy tubes are heli-arc welded at the joints, brushed to a shine; something that plays into the chromed-out finish of our TRX. The heel guards boast the same looks, as well as construction that is much stronger than the plastic guards that came stock with the machine. These are a perfect addition for the trails this machine was built to ride.


Our next area of focus in this build was the drive components. We chose Maxxis Razr II tires because the dynamic tread is an excellent choice for all-around trail riding as well as for competition. We mounted the tires on Douglas A5 wheels in matte black—a color that complements our quad’s traditional Honda red. These durable rims are constructed of aluminum, providing a perfect combination of strength and weight.

New Tires and Wheels on the Honda TRX400EX

Along with the new wheels, our drive system needed a new axle. The Tusk Adjustable Width Axle fit the bill. We opted to set ours at its widest setting to accommodate our trail riding. Up front, we added some spacers to match the wide, aggressive stance we have in the rear.

For a fresh set of brakes, we counted on the Tusk Typhoon Brake Rotors and sintered brake pads. The rotors are specifically designed to control heat while riding, which improves stopping performance and increases safety.

The chain and sprocket on this machine were really worn out, so we turned to the Primary Drive Steel Kit and X-Ring Chain. This kit includes both sprockets and a low-friction X-ring chain.

Chains and Sprockets on the Honda TRX400EX

We always want to keep our machines safe in case a chain ever catches a rock or snaps, so we added the Tusk Billet Aluminum Case Saver. Machined from 6061 aluminum, the kit provides stainless steel hardware for installation and allows us to ride the most technical trails confidently.

We replaced the old shift lever with a Tusk Folding Shift Lever, giving the machine a fresher look.


The Factory Effects All Grip seat cover replaced our worn out seat. Triple-stitched and rubberized for durability, this new cover sports locator pockets at each end to help with installation. This seat gives you a lot more grip than the stock seat cover, which will help significantly improve handling on the trail.

We upgraded the stock handlebars to the Pro-Taper SE STV High-End. Lighter and stronger than the stock steel, these aluminum bars also feature a sportier bend for better control.

Pro-Taper Handlebars and ODI Grips on the Honda TRX400EX

To hang on to those bars, we attached ODI Lock-On grips. Not only do the improve handling and grip but thanks to ODI’s patented snap-caps, they are really easy to install.

ODI Lock-On Grips on the Honda TRX400EX

The TRX doesn’t have a kick-start, so making sure your batter is fully charged and in great condition is really important. We chose to grab a Tusk. We chose the Tusk Tech-Core battery because of its ability to deliver unfailing starts even in tough, off-road conditions. It’s also maintenance-free with a leak-proof cap and seal.

Headlights on the the Honda TRX400EX

To light up the trail we’ve installed two Tusk Super White Bulbs in the headlight. They use the same 35/35W draw as stock, but deliver a full 60/60W output. With them, we can see and be seen with a brighter, stronger beam whenever we’re taking our TRX out in the dark.


How do you make an already good-looking quad stunning? For us, it was easy. We got with Attack Graphics, and decked our TRX out with one of their custom graphics kits. The kit dressed up our smart quad with 14 mil scratch-resistant, laminated vinyl that will last.

A Closer Look at the Honda TRX400EX

In addition to our graphics, we wanted to tie the whole look of the machine together with a billet aluminum Gas Cap, Reservoir cap, and some engine plugs all from Tusk to add some nice finishing touches to our machine.

Graphics on the Honda TRX400EX

For a final touch, the Tusk Engine Plug Kit, was the perfect fit. The kit includes both timing plugs found on the stator cover (O-rings not included) and uses a hex center for easy application with an Allen wrench. A fresh set of plugs is always practical, and the dash of color rounded out our machine’s aesthetics.


We love the TRX400 because you can find great deals on barely ridden machines. So, whether you are buying one to build or just want to freshen up the one in the garage, we hope this build provides a little bit of inspiration. From hundreds of aftermarket Honda ATV parts to a wide array of Honda OEM parts, you have options for rejuvenating your own machine. Almost twenty years old, and ours is still turning heads on the trail.

The Built Machine

Parts Available at Rocky Mountain ATV/MC
QA Parts Cylinder and Piston Kit Hot Cams Camshaft Kit (Stage 1) Tusk Competition Clutch Kit
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Pro X Air Filter Lexx MXe Slip-On Silencer Tusk Comp Series Aluminum Front Bumper
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Ricochet A-Arm Guards Ricochet Full Chassis Skid Plate Ricochet Swing Arm Guard
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Maxxis Razr II Tire Maxxis Razr II Tire Douglas A5 Wheel
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Tusk Adjustable Width Racing Axle Tusk Stainless Steel Typhoon Brake Rotor Primary Drive Steel Kit and X-Ring Chain
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Tusk Billet Aluminum Case Saver Tusk Folding Shift Lever Factory Effex All Grip Seat Cover
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ProTaper SE High-Bend Handlebar Odi ATV Lock-On Grips Tusk Tech-core Battery
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Tusk Anodized Front Brake Reservoir Cap Tusk Billet Aluminum Engine Plug Kit Tusk Foot Peg Nerf Bars With Heel Guards
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Tusk Super White Bulb Attack Graphics ATV Kit Tusk Billet Aluminum Gas Cap
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