| Specification | Data |
|---|---|
| Production Years | 1978 – 1983 |
| Engine Type | Single-cylinder, 2-stroke |
| Transmission Oil | SAE 10W-30 (API Service SE) (0.7 L) |
| Spark Plug | NGK BR8ES |
| Battery Type | 6N6-3B (6-Volt) |
| Tire Size (F/R) | 2.75-21 4PR / 3.50-18 4PR |
| Tire Pressure (F/R) | 1.2 bar (17 psi) / 1.5 bar (21 psi) |
Engineering Highlight: The Monocross Revolution
The Yamaha DT 175 MX (2K4 series) holds a prestigious place in motorcycle history as the machine that brought the revolutionary Monocross cantilever rear suspension to the masses. Unlike its competitors of the late 70s that still utilized traditional twin-shock setups, the 2K4 utilized a single, nitrogen-charged shock absorber hidden under the fuel tank. This engineering feat, derived directly from Yamaha’s YZ-series motocross winners, significantly improved wheel travel and centralized mass, making it the most capable dual-sport in its class.
Technical Review: Performance and Reliability
At the heart of the 2K4 is a 171cc two-stroke engine featuring Yamaha’s 7-port induction and the iconic Torque Induction reed valve system. This setup provided a surprisingly broad powerband for a small-displacement two-stroke, delivering roughly 15-16 horsepower. The lightweight chassis (approx. 98kg dry) combined with the 21-inch front wheel makes it an exceptionally nimble off-road tool even by modern standards.
Transmission & Lubrication
Maintenance of the 2K4 is straightforward but critical for longevity. The gearbox requires 0.7 Liters of SAE 10W-30 oil. While modern synthetics are available, ensuring the oil meets the API Service SE (or better) specification is vital for clutch plate compatibility. The Autolube system, Yamaha’s automatic oil injection, is generally reliable, but many enthusiasts prefer to check the pump adjustment regularly to ensure the correct 2-stroke oil mix ratio.
Electrical & Ignition
The 2K4 utilizes a 6-volt electrical system powered by a 6N6-3B battery. For optimal combustion and heat range management, the NGK BR8ES spark plug is the factory-standard recommendation. Owners should ensure the plug gap is set correctly to maintain a crisp throttle response, especially during low-speed trail riding where carbon fouling can occur.
Maintenance Guide & Best Practices
- Chassis Care: Periodically grease the Monocross linkage points. These are often overlooked and can lead to expensive pivot wear if run dry.
- Tire Management: For mixed-use riding, maintain 17 psi (front) and 21 psi (rear). If riding exclusively on soft terrain, these can be lowered slightly, but rim locks are recommended to prevent valve stem shearing.
- Air Filter: The foam element should be cleaned and re-oiled every 1,000 miles, or more frequently in dusty conditions, to protect the 2-stroke top end from abrasive particles.
Frequently Asked Questions
What is the fuel capacity of the DT 175 MX?
The fuel tank typically holds approximately 7 liters, providing a decent range for trail excursions given the engine’s efficiency.
Can I upgrade the 6V system to 12V?
Yes, many owners opt for a 12V conversion kit to improve lighting performance, though this requires replacing all bulbs, the battery, and the regulator/rectifier.
What is the significance of the ‘2K4’ designation?
The ‘2K4’ is the model prefix used by Yamaha to identify this specific generation (1978-1983) of the DT 175 MX, ensuring correct parts identification during restoration.