Types of Honda CR125 Engine
The Honda CR125 has evolved through several engine variants, each with distinct characteristics and performance profiles. Understanding these differences is crucial for riders and collectors alike.
Honda CR125R
The CR125R is Honda's flagship two-stroke dirt bike model, renowned for its exceptional performance characteristics:
- Engine Type: 125cc liquid-cooled two-stroke single-cylinder
- Frame: Lightweight steel construction for superior maneuverability
- Power Output: High-revving engine with impressive power-to-weight ratio
- Braking: Front and rear disc brakes with reliable stopping power
- Suspension: Advanced front telescopic forks and rear monoshock system
The CR125R excels on various terrains thanks to its responsive handling and powerful acceleration, making it a favorite among competitive riders.
Honda CR125M
The CR125M represents Honda's innovative approach to dirt bike design:
- Engine Type: 125cc four-stroke engine (introduced in 1973)
- Frame: Pioneering aluminum frame design
- Air Filtration: Advanced system for optimal airflow and engine protection
- Transmission: 5-speed system for versatile riding conditions
- Suspension: Front telescopic forks with rear twin shock configuration
The CR125M established many design standards that influenced future dirt bike development across the industry.
Honda CR125R Big Wheel
The Big Wheel variant offers enhanced capabilities for specific riding environments:
- Wheel Size: Larger diameter wheels and tires than standard models
- Terrain Capability: Excels in sand, mud, and rocky conditions
- Engine Performance: Same powerful two-stroke engine as the standard CR125R
- Braking: Front and rear disc braking system for reliable control
The Big Wheel configuration offers improved ground clearance and stability over rough terrain, making it ideal for enduro or cross-country applications.
CR125R
CR125M
CR125R Big Wheel
Two-stroke
Four-stroke
Two-stroke
Motocross & Racing
Technical Riding
Rough Terrain
Steel
Aluminum
Steel
Pro Tip: When identifying a CR125 model, check the VIN and engine number. The engine number is typically stamped on the right crankcase and begins with specific model identifiers.
Specifications and Maintenance of Honda CR125 Engine
Proper maintenance is essential for maximizing the performance and lifespan of any Honda CR125 engine. Here's a comprehensive breakdown of key maintenance areas and specifications:
Fuel Requirements
- Fuel Type: Premium unleaded (minimum 91 octane)
- Tank Capacity: 2.0 gallons (7.6 liters)
- Fuel Quality Impact: High-octane fuel reduces engine knocking and optimizes performance
The CR125R's high-performance engine demands quality fuel to maintain optimal combustion and prevent premature engine wear. Using lower-grade fuel can result in performance losses and potential engine damage.
Oil Requirements
- Oil Type: Two-stroke engine oil for racing applications
- Mixing Ratio: 32:1 (1 quart oil per 8 gallons of fuel)
- Recommended Brands: Pro Honda HP2, Maxima Castor 927
Proper oil mixture is critical for two-stroke engines as the oil lubricates internal components while being consumed during combustion. Always follow manufacturer mixing instructions for optimal engine performance.
Air Filtration
- Filter Type: Foam air filter
- Inspection Frequency: Before and after each ride
- Cleaning Method: Warm water with dish soap, rinse thoroughly
The air filter is your engine's first line of defense against damaging particles. Regular cleaning and maintenance are especially important when riding in dusty conditions.
Cooling System
- System Type: Liquid-cooled with radiator
- Coolant Check: Verify level is between min/max marks before each ride
- Coolant Change Interval: Every 2 years or 24,000 miles (39,000 km)
The cooling system prevents engine overheating during intense riding sessions. Regular coolant changes and system inspections help maintain optimal engine operating temperatures.
Wheels and Tires
- Wheel Sizes: 21-inch front, 19-inch rear (standard)
- Maintenance: Regular spoke tension checks
- Tire Pressure: Adjust according to terrain and riding conditions
Proper wheel maintenance ensures stability and handling performance. Always inspect wheels before riding for loose spokes or damage.
Suspension System
- Components: Front forks and rear shock absorber
- Oil Change Interval: Every 30 hours of riding time
- Inspection: Check for leaks and proper operation regularly
The suspension system absorbs impacts and maintains tire contact with the ground. Regular oil changes ensure smooth operation and consistent performance.
| Maintenance Task | Frequency | Special Requirements |
|---|---|---|
| Air Filter Cleaning | Before/After Each Ride | More frequent in dusty conditions |
| Oil/Fuel Mixture | Every Refueling | 32:1 ratio with premium oil |
| Coolant Check | Before Each Ride | Maintain level between min/max marks |
| Coolant Replacement | Every 2 Years | Use Honda-approved coolant |
| Suspension Oil Change | Every 30 Hours | Use specified viscosity oil |
| Spoke Tension Check | Before Each Ride | Tighten as needed |
Important: Never substitute regular gasoline for the required premium fuel in a CR125R engine. Lower octane fuels can cause detonation, pre-ignition, and serious engine damage, especially in high-performance two-stroke engines.
How to Choose Honda CR125 Engines
Selecting the right Honda CR125 engine requires careful consideration of several key factors to ensure you get the best performance for your specific needs and riding style.
Rider Experience Level
Different CR125 engine variants are better suited to different rider experience levels:
- Beginners: Look for engines with milder power delivery and more predictable performance characteristics
- Intermediate: Balance of power and controllability
- Advanced: High-revving engines with aggressive power bands for maximum performance
A mismatch between rider skill and engine characteristics can lead to difficult handling and potential safety issues.
Riding Style & Environment
Your preferred riding discipline should heavily influence engine selection:
- Trail Riding: Engines with strong low-end torque for navigating technical terrain
- Motocross: High-RPM power delivery for competitive racing
- Enduro/Cross-Country: Balance of tractable power delivery and endurance
The Big Wheel variant may be preferable for riders frequently tackling rough terrain due to its improved ground clearance.
Engine Condition Assessment
When evaluating a used CR125 engine, check these critical aspects:
- Compression: Should be within manufacturer specifications (typically 170-210 PSI)
- Piston Condition: Inspect for scoring or damage
- Crankshaft: Check for smooth operation without excessive play
- Transmission: Verify all gears engage properly
A professional inspection may be worthwhile before purchasing a used engine to avoid costly repairs later.
Budget Considerations
Financial factors extend beyond the initial purchase price:
- Initial Cost: Prices vary by model year, condition, and modifications
- Maintenance Expenses: Two-stroke engines require frequent top-end rebuilds
- Parts Availability: Newer models typically have better parts support
- Fuel Consumption: Two-strokes generally consume more fuel and oil
Consider the total cost of ownership, not just the purchase price, when budgeting for your CR125.
| Selection Factor | Considerations | Importance |
|---|---|---|
| Engine Year/Model | Later models (2000-2007) offer improved power characteristics | High |
| Engine Hours | Two-stroke engines typically need rebuilds every 15-30 racing hours | Critical |
| Modifications | Aftermarket parts can enhance performance but may affect reliability | Medium |
| Documentation | Service records indicate proper maintenance history | High |
| Compatibility | Ensure engine matches your frame year/model | Critical |
Expert Advice: When possible, hear the engine run before purchasing. Listen for unusual noises, observe smoke color (blue smoke can indicate excessive oil consumption), and check for smooth idle and throttle response.
How to DIY and Replace Honda CR125 Engine
Replacing a Honda CR125 engine is a significant undertaking that requires careful planning and mechanical knowledge. While challenging, this process can be accomplished by dedicated enthusiasts with the right tools and approach.
Gather Tools and Parts
Before beginning, assemble all necessary tools and replacement components:
- Socket set (metric)
- Torque wrench
- Service manual (specific to your model year)
- Motorcycle stand
- Engine hoist or lifting mechanism
- Gasket set
- Replacement parts as needed
Prepare the Motorcycle
Create a safe working environment and prepare the bike:
- Disconnect the battery (negative terminal first)
- Place the motorcycle on a secure stand
- Clean the exterior to prevent contamination
- Take reference photos to aid reassembly
Remove External Components
Disconnect and remove all peripherals connected to the engine:
- Air filter and airbox
- Exhaust system (header and silencer)
- Carburetor
- Throttle and clutch cables
- CDI unit and electrical connections
- Radiator and cooling lines
Drain Fluids
Remove all fluids from the engine:
- Coolant (collect in approved container)
- Transmission oil (if separate from fuel mix)
- Dispose of fluids according to local regulations
Disconnect Engine Mounts
Remove the bolts securing the engine to the frame:
- Identify all engine mounting points (typically 3-4 locations)
- Support the engine before removing final mounts
- Note the position of any spacers or special hardware
Remove the Engine
Carefully extract the engine from the frame:
- Use an engine hoist or get assistance for safe lifting
- Move the engine slowly to avoid damaging frame or components
- Place on a clean, stable work surface
Install New/Rebuilt Engine
Reverse the removal process to install the replacement engine:
- Carefully align engine with mounting points
- Install mounting bolts but do not fully tighten until all are in place
- Torque all bolts to factory specifications in the correct sequence
Reconnect Components
Reattach all external components in reverse order of removal:
- Verify proper routing of all cables and hoses
- Ensure electrical connections are secure and properly seated
- Install new gaskets where needed
Refill Fluids and Test
Prepare the engine for operation:
- Add fresh coolant to the cooling system
- If applicable, add transmission oil
- Prepare proper fuel/oil mixture for initial startup
- Check for leaks before starting
- Start engine and verify proper operation
Safety Warning: Engine replacement involves heavy components and potential exposure to harmful fluids. Always wear appropriate safety gear including gloves and eye protection. Never work under an unsecured motorcycle or engine.
Pro Tip: After engine installation, perform a comprehensive break-in procedure according to manufacturer guidelines. Typically this involves varying engine speeds and avoiding full throttle operation for the first few hours of running time.
Frequently Asked Questions
The Honda CR125 is a 125cc two-stroke single-cylinder dirt bike engine that was manufactured by Honda from 1973 to 2007. It's part of Honda's CR (Competition Racing) series of off-road motorcycles. This lightweight engine is characterized by its high-revving performance, making it especially popular in motocross racing. The engine underwent numerous refinements throughout its production run, with later models featuring improved power delivery and reliability.
The Honda CR125 dirt bike is renowned for several distinctive characteristics:
- Exceptional power-to-weight ratio delivering impressive acceleration
- Nimble handling due to its lightweight construction
- High-revving two-stroke engine with a distinctive power band
- Competitive racing heritage with numerous championships
- Reliability compared to other two-stroke motorcycles
- Extensive aftermarket support and community knowledge base
These qualities have made it a favorite among motocross enthusiasts and competitive riders for decades.
Yes, the Honda CR125 can handle modern motocross tracks, though riders may need to adapt their technique. While modern four-stroke bikes have become the dominant force in professional motocross, a well-maintained CR125 remains competitive, especially in the hands of a skilled rider.
Key considerations for riding a CR125 on modern tracks include:
- Maintaining momentum through corners due to the two-stroke power delivery
- Utilizing the bike's lighter weight to maneuver through technical sections
- Potentially upgrading suspension components to handle larger jumps and obstacles
- Focusing on smooth riding technique to stay in the powerband
Many riders still prefer the CR125's handling characteristics and enjoy the challenge of riding a two-stroke on modern tracks.
No, Honda discontinued production of the CR125 in 2007. This decision came as the motocross industry shifted toward four-stroke engines due to changing emissions regulations and evolving racing preferences. Despite ending production over a decade ago, the CR125 maintains a strong following in the used market and vintage racing scenes.
While new models aren't available, there are still many options for enthusiasts:
- Purchasing used CR125 models (2000-2007 years are particularly sought after)
- Restoring vintage CR125 motorcycles
- Participating in two-stroke-specific racing classes and events
The enduring popularity of the CR125 has helped maintain strong parts availability and community support even years after production ended.
While generally reliable, Honda CR125 engines can develop several common issues that owners should monitor:
- Piston and ring wear - Two-stroke engines typically require more frequent top-end rebuilds (every 15-30 hours for racing)
- Crank bearing failure - Can occur due to water contamination or improper maintenance
- Power valve issues - Carbon buildup can affect performance (requires regular cleaning)
- Ignition problems - CDI units and coils can fail, especially on older models
- Water pump seal leakage - Can cause coolant to mix with transmission oil
Most of these issues can be prevented through proper maintenance and timely rebuilds. Regular inspection of the top end and careful attention to proper fuel/oil mixture ratios significantly extend engine life.