The O.S. Max 25LA is a highly popular, budget-friendly .25 cubic inch (4.1cc) two-stroke glow engine manufactured by O.S. Engines. Designed primarily for RC airplane beginners and sport flyers, it is well-regarded for its lightweight construction, reliability, and easy handling
Technical Specifications
Displacement: 0.2485 cu in (4.07 cc)
Bore & Stroke: 0.7087 in (18.0 mm) x 0.63 in (16.0 mm)
Power Output: 0.6 hp @ 15,000 RPM
Practical RPM Range: 2,500 to 16,000 RPM
Weight: 6.9 oz (197 g) without muffler
Crankshaft Style: Plain bushing (does not use ball bearings)
Key Features
Remote Needle Valve: The #20H carburetor uses a rear-mounted needle valve assembly. This allows you to safely adjust fuel mixtures away from the spinning propeller.
Plain Bushing Design: Unlike the higher-performance O.S. FX series, the LA line features a plain bronze bushing on the crankshaft. This sacrifices a bit of top-end power but makes the engine significantly lighter, more economical, and easier for beginners to manage.
Distinct Visual Options: The engine was manufactured in both a standard natural aluminum finish and a signature blue matte coating.
Reinforced Crankcase: Extra structural webbing helps prevent damage during rough landings or learner crashes.
Fuel: Recommended formulation contains 5% to 20% nitro with a minimum of 18% oil content by volume. A generous oil content is crucial for plain bushing engines to maintain longevity.
Glow Plug: Pairs ideally with a standard O.S. #A3 glow plug (or standard O.S. No. 6).Recommended Propellers:
Generally performs best on sport or scale aircraft using 9×5, 9×6, or 10×4 sized propellers.
