Description

Kawasaki Mule SX 4×4 FJ400 Engine Rebuild Service (2016–2025)

The Kawasaki Mule SX 4×4 FJ400 is built for dependable utility use, steady low-end response, and long days on the job. However, when internal wear starts to show up, you may notice hard starting, weak compression, oil leaks, smoking, or power that feels inconsistent under load.

At REV6, we tear your engine down completely, inspect the core, and rebuild it with refreshed internals and corrected clearances. As a result, your Mule SX gets the clean starts, smoother operation, and reliable power it needs to get back to work.

Core Requirement

Core required: A rebuildable Kawasaki Mule SX 4×4 FJ400 engine core must be supplied for this service. Your rebuild begins once we receive your engine and complete the inspection process.

After your order is placed, we’ll send a prepaid shipping label and coordinate pickup. Before shipping, remove your exhaust, fuel-related components, electrical parts, and sensors. After that, we handle the teardown, rebuild, inspection, and return shipping.

For step-by-step instructions, visit our Help Center.

If you want to spread out the cost, check out our flexible payment options.

What’s Included in the Rebuild

• Full core inspection to confirm serviceability before rebuild begins
• Crankshaft and rod assessment for long-term durability
• Cylinder bore service — trued, straightened, and crosshatched for proper sealing
• New pistons and rings for restored compression and smoother operation
• Complete gasket kit for dependable sealing
• New oil seals to help prevent leaks and protect lubrication
• Valve guide seals replaced to control oil use and reduce wear
• Valve and head service — valves ground and lash set to proper specifications
• Assembly completed by an experienced technician
• Final quality control inspection before shipment

Note: Final build details depend on your engine’s condition.

Built for Mule SX Reliability

The Mule SX FJ400 needs clean starts, strong sealing, accurate clearances, and dependable bottom-end condition to stay useful day after day. Because of that, we focus on crankshaft condition, rod health, cylinder finish, piston fitment, valve sealing, gasket integrity, and oil control throughout the rebuild.

In turn, your rebuilt engine delivers steadier operation, stronger compression, and dependable utility performance when your machine is back in service.

Turnaround Time

Typical turnaround time is about 2 weeks after your engine core arrives, depending on core condition and parts availability.

Warranty & Support

Every rebuild includes a 1-year warranty. In addition, eligible engine builds can be upgraded to a 2-year no-fault plan for extra protection.

Review coverage in our warranty policy, browse answers in our FAQ, or contact our team before ordering.

If you are comparing rebuild options, our Engine Rebuild Kit Guide can help you decide what fits your project best. You can also read more on the REV6 Blog and watch helpful content on our YouTube channel.

Take Action

If your Kawasaki Mule SX 4×4 FJ400 is hard starting, losing compression, leaking oil, or showing signs of internal wear, now’s the time to rebuild it the right way.

Get back in service with dependable power, smoother operation, and confidence in your rebuilt engine.

We proudly support veterans and active servicemembers with available discounts—thank you for your service.