This is the O.S. Max .91 HZ F3C Competition Helicopter Engine. The O.S. MAX-91SZ-H RING was the champion engine of the FAI F3C World Championship in 2005 and 2007 consecutively. It performed perfectly from stable hovering to dynamic aerobatic maneuver. Based on this distinguished engine, MAX-91HZ has been improved greatly corresponding to users’ requests in the field of F3C. The slim heatsink head fits into fan shroud without having to cut it. So the fresh air reaches the heatsink head and the carburetor without any loss.

The improved areas are the scavenging port, exhaust port, crankcase heatsink, and the new heatsink head. The combination of these modifications contributes to cool performance and stable power output. In addition, the engine noise is reduced by improving the overall balance of the engine for smoother higher engine performance. MAX-91HZ has succeeded in acquiring champion quality to win FAI F3C keeping its “easy to tune” and “consistent R.P.M.” nature achieved by the fine tunings through our unrelenting effort.

Features

• The slim heatsink head fits into the fan shroud without having to cut it. So the fresh air through the fan cover effectively cools down the engine. The die cast head doesn’t create annoying high-frequency noise.
• The new carburetor 61B is equipped with a thermo-insulator and in-flight needle control valve as standard accessories. Its fuel route is refined to correspond to high power. Double O-ringed main needle and O-ringed carburetor rotor prevent air leakage and engine power fluctuation. This new system secures stable and precise carburetor adjustment.
• The newly designed back plate fulfils a role of heatsink. It is efficiently cooled down by the fresh air through the air inlets of full-covered helicopter body shell.
• The piston is modified to attain a lighter body and better performance. The combustion gas presses on the piston ring from within through the five holes laid out on the piston top to minimize the blow-by gas.So the combustion energy is effectively transferred to the crankshaft.

Specifications
Displacement: 0.91 cu in (14.95 cc)
Bore: 1.09" (27.7mm)
Stroke: 0.98" (24.8mm)
Glow Plug: #8
Output: 3.4 hp @ 15,000 RPM
Practical RPM Range: 2000-16,000
Weight Without Muffler: 1.36lb (618g)

Includes
O.S. Max .91 Hz Ringed Helicopter Engine
Glow Plug No.8
Needle Control Arm
Cylinder Head Gasket (0.2mm)
Needle Ajusting Screw (M2.6 X 5) 2 Pcs
Carburetor Complete 61B
Instruction Manual