This is the O.S. Max .91 FX 2-Stroke Ringed Engine with Muffler.  This engine works very well in sport and aerobatic aircraft.  This engine comes with the OS Two-Year Limited Warranty.

Features:

• One-piece crankcase
• Twin ball bearing-supported crankshaft
• Schnuerle porting (AKA Schnuerle scavenging)
• Aluminum piston, steel cylinder liner and iron piston ring
• Side exhaust with muffler with rotatable exhaust outlet
• Carburetor with remote needle mounted on the engine back plate (to keep fingers away from the spinning propeller)
• Two-year warranty

Includes:
One Expansion style muffler (#E-4010) with screws
One Assembled engine with carb.
One package illustrated instructions, parts list, and O.S. decal
One O.S. #8 glow plug

Specifications:
Displacement:      14.95cc (0.912 cu in)
RPM range:         2,000 - 16,000
Bore:              27.7mm (1.090")
Stroke:            24.8mm (0.976")
Compression Ratio: 10.1 : 1
Weight: 550g (19.42oz)   24.3oz w/muffler
Horsepower:        2.8 BHP at 15,000 RPM

Length: 96mm the distance from the backplate to drive washer
Width: 42.6mm width of engine neglecting engine mounting flanges
52mm distance between centers of the mounting holes
Height: 103mm
Crankshaft Thread Size: 5/16-24