This is the the O.S. Max .25LA Aircraft Engine with Muffler.
Meets Requirments of Beginners and Sport Flyers.

FEATURES: One-piece natural finish crankcase
Two bronze crankshaft bushings (sometimes called Oilite bearings)
Schnuerle porting (Schnuerle scavenging)
Side exhaust
Nylon backplate
#20H carb with remote needle valve assembly

REQUIRES: Glow Fuel with 5-15% Nitromethane and 20% (minimum) lubricant content
Glow starter plug wrench and field equipment

SPECIFICATIONS:
Construction: Aluminum 1-piece crankcase piston cylinder head
crankshaft connecting rod and crankshaft. Chrome-plated
Brass cylinder.
Displacement: 4.07cc (0.249 cu. in.)
Bore: 18.0mm (.709")
Stroke: 16.0mm (.630")
Horsepower: 0.6 BHP at 15 000 RPM
Weight: 7.0oz w/o muffler (9.5oz w/ muffler)
Length: 67.5mm (2.65") distance/backplate to front of drive washer
89.5mm (3.52") distance from backplate to prop adapter
Width: 29mm (1.14") width of engine neglecting mounting flanges
Distance Between Mounting Holes Same Side: 14.4mm (.56")
Distance Between Mounting Holes Opposite Side: 33mm (1.29")
Height: 74.5mm (2.93") from bottom of mount tab/top of cylinder head
Crankshaft Thread Size: 1/4-28
Recommended Props: Break In: 9x5
Trainer and Sport Models: 9x5 9x6
Practical RPM Range: 2 500 - 16 000 RPM