Marine thermal engine O.S. 61 VR-M 9.95 cm3

The O.S. MAX-61 VR-M engine: a reference in competitive model naval modeling

Launched in the late 1970s, the O.S. MAX-61 VR-M succeeds the RSR-M series and marks a significant evolution in the marine range of the Japanese manufacturer.

Its designation VR refers to a rear disc rotary intake and rear exhaust (Ventral Rear), specially designed to provide excellent cylinder filling and high-speed performance.

With its displacement of 9.95 cm³, this engine develops up to 2.8 horsepower at 22,000 rpm, with a range of use between 2,500 and 25,000 rpm.

It provides very sharp accelerations, high top speed, and remarkable operational consistency.

ABC technology designed for competition

The MAX-61 VR-M uses an ABC (Aluminum - Brass - Chrome) construction, a technology that has greatly contributed to the reputation of O.S. engines. This design ensures excellent compression, low wear, and very good performance stability even during intensive use.

The engine also benefits from a three-transfer Schnürle scavenging, a carburetor specially developed for high power, and water cooling to maintain an optimal temperature during long acceleration phases.

An engine designed for fast RC boats

The 61 VR-M was developed to equip high-speed radio-controlled boats, hydros, monohulls, and other competition hulls.

Its specific design includes:

• water-cooled cylinder head;
• rear intake optimizing filling;
• crankshaft designed for flexible drive;
• excellent high-speed performance.

This architecture makes it a particularly popular engine for classic RC boat restoration projects.

A highly sought-after engine

Although it has not been manufactured for a long time, the O.S. MAX-61 VR-M remains a safe bet among collectors and enthusiasts of thermal modeling.

Its machining quality, ease of starting, precise adjustments, and legendary reliability explain why it is still one of the most sought-after Japanese marine engines of its generation.

Technical specifications

• Displacement: 9.95 cm³
• Bore: 24 mm
• Stroke: 22 mm
• Maximum power: 2.8 hp at 22,000 rpm
• Operating range: 2,500 to 25,000 rpm
• Type: 2-stroke glow engine
• Technology: ABC
• Scavenging: three-transfer Schnürle
• Cooling: water-cooled
• Weight: 910 g
• Use: high-speed and competition radio-controlled boats

Why choose the O.S. MAX-61 VR-M?

• Japanese manufacturing by O.S. Engines
• Engine specially designed for nautical competition
• High-performance ABC technology
• Excellent power and high speed
• Recognized reliability for several decades
• Collectible piece sought after by enthusiasts of O.S. marine engines

The O.S. MAX-61 VR-M represents one of the most remarkable achievements of O.S. Engines in the field of marine thermal engines.

Its performance, manufacturing quality, and longevity allow it to maintain an excellent reputation among demanding modelers wishing to equip or restore a competitive RC boat.