2002 Honda 400EX: 2‑Stroke or 4‑Stroke?

The 2002 Honda 400EX (also known as the TRX400EX) is a 4‑stroke, single‑cylinder, air‑cooled ATV. It uses a durable, torque‑friendly engine derived from Honda’s XR400R off‑road motorcycle, optimized for trail and sport riding rather than the peaky powerband typical of 2‑strokes.

What the 400EX Engine Is

Honda built the 400EX around a 397cc four‑stroke powerplant designed for broad, manageable power and long‑term reliability. The engine features a single overhead cam, carbureted fueling, air cooling with an external oil cooler, and a dry‑sump lubrication system. In 2002 it came with electric start and a 5‑speed manual gearbox; reverse was not available on that model year.

Why Honda Chose a 4‑Stroke for the 400EX

At the turn of the 2000s, sport ATVs were shifting toward four‑stroke engines for their tractable power and reduced maintenance frequency compared with high‑strung two‑strokes. Honda’s decision aligned with rider demand for dependable trail and dune performance, ease of use, and emissions considerations.

• Rideability: Broad, predictable torque suited to trails, dunes, and technical terrain.
• Durability: Lower peak stresses than comparable 2‑strokes, aiding engine longevity.
• Maintenance cadence: No premix; valve adjustments at intervals rather than frequent top‑end rebuilds.
• Noise and emissions: Generally quieter with cleaner burn relative to same‑era 2‑strokes.
• Starting: Electric start complements the 4‑stroke’s user‑friendly character.

Taken together, these traits made the 400EX a benchmark for riders seeking a dependable sport ATV that balances performance with low drama ownership.

Key Engine and Drivetrain Highlights (2002 Model)

While the headline is that it’s a four‑stroke, several supporting specs define how the 400EX feels on the trail. Below are core characteristics riders typically care about.

• Engine: 397cc air‑cooled, SOHC, 4‑stroke single derived from the XR400R.
• Fueling: Keihin carburetor (non‑fuel‑injected), tuned for strong midrange.
• Lubrication: Dry‑sump system with an external oil tank and front‑mounted oil cooler.
• Starting: Electric start from the factory.
• Transmission: 5‑speed manual; no reverse on the 2002 model year.
• Final drive: O‑ring chain.
• Cooling: Air‑cooled with supplemental oil cooling for thermal stability.

These elements contribute to the 400EX’s reputation for linear power delivery, straightforward upkeep, and a forgiving learning curve for a wide range of riders.

How to Tell a 2‑Stroke from a 4‑Stroke on an ATV Like the 400EX

If you’re inspecting an ATV and unsure about the engine type, a few quick visual and behavioral cues can help you confirm what you’re looking at.

• Exhaust system: 2‑strokes typically have a large “expansion chamber” ahead of the silencer; the 400EX does not.
• Fuel/oil handling: 2‑strokes often require premixed fuel; the 400EX uses a separate engine oil system.
• Power character: 2‑strokes deliver a sudden “hit”; the 400EX’s 4‑stroke pulls smoothly off idle through midrange.
• Sound: 2‑strokes have a higher‑pitched, brappy exhaust note; the 400EX has a deeper thump.
• Valvetrain: 4‑strokes have cam/valve components and usually valve adjustment caps; 2‑strokes lack a valvetrain.

Using these signs, even a quick glance or a short test ride can typically confirm that a 400EX is a four‑stroke machine.

Bottom Line

The 2002 Honda 400EX is unequivocally a 4‑stroke ATV. Its engine design prioritizes tractable power, reliability, and ease of ownership—key reasons it became one of the most respected sport quads of its era.

Summary

The 2002 Honda 400EX (TRX400EX) runs a 4‑stroke, air‑cooled, SOHC single with electric start and a 5‑speed manual (no reverse in 2002). Built off the XR400R platform, it trades the abrupt punch of 2‑strokes for smooth torque, longevity, and rider‑friendly manners.

How much is a 2001 Honda 400EX worth?

The 2001 Honda 400EX, also known as the TRX400EX Sportrax, has an estimated value between $1,105 and $4,320, depending on its condition. J.D. Power says the values are: Excellent ($4,320), Very Good ($3,045), Good ($1,950), and Fair ($1,105). However, the actual market value can vary based on location, specific features, and overall condition, according to Classic.com. 
Factors Affecting Value:

• Condition: As indicated by J.D. Power, the condition of the ATV significantly impacts its value. Excellent condition models will command a higher price than those in fair or poor condition. 
• Modifications and Upgrades: Aftermarket modifications and performance upgrades can increase or decrease the value depending on the buyer’s preferences and the quality of the work. 
• Location: The local market conditions and demand for ATVs can influence the price. 
• Demand: Popularity and demand for the Honda 400EX, particularly among sport ATV enthusiasts, can also affect its value. 
• Wear and Tear: Excessive wear and tear, such as a worn-out engine or damaged bodywork, will decrease the value. 
• Rebuilds: If the ATV has undergone a recent rebuild or major repair, it may be worth more than one that has not. 

Is the Honda 400EX a 2 stroke or 4 stroke?

Honda 400EX specs include a high performance 397cc dry-sump, air-cooled, four-stroke single cylinder engine. A radial four valve combustion chamber (RFVC) takes care of creating horsepower.

What is the top speed of the 2002 Honda 400EX?

The top speed of a 2002 Honda 400EX (TRX400EX) is generally cited as being around 65 mph to 72 mph, though this can vary based on specific conditions and modifications. Some sources give a rating of around 65 mph, while others, and actual rider tests, indicate speeds up to 72 mph have been reached. 

• Advertised Speed: Some sources, like webBikeWorld and Ron Bishop Motorcycles, list a top speed around the 72 mph mark. 
• Real-World Performance: Rider tests and videos show the 400EX can reach or exceed 65 mph. 
• Factors Affecting Speed: The actual top speed can be affected by factors such as rider weight, terrain, tire pressure, and whether the ATV is stock or has aftermarket modifications. 

Are 400exs reliable?

The 400EX is one of the greats, up there with the Yamaha Banshee 350. Where the Banshee has an extraordinary powerband that can almost suck the vehicle right from under your hands, the 400EX has reliability and ease of use.