The blower supplies the fresh air required for combustion and scavenging. Its operation is similar to that of a
gear-type oil pump. Two hollow double-lobe rotors revolve in a housing bolted to the side of the in-line engines
(Fig. 1). The revolving motion of the rotors provides a continuous and uniform displacement of air.
The blower rotors are pinned to the rotor shafts. The rotor shafts are steel and the blower end plates are
aluminum, providing for a compatible bearing arrangement.
Gears located on the splined end of the rotor shafts space the rotor lobes with a close tolerance. Since the
lobes of the two rotors do not touch at any time, no lubrication is required.
Lip-type oil seals are used in both the front and rear end plates on current engines. The seals prevent air
leakage past the blower rotor shaft bearing surfaces and also keep the oil, used for lubricating the blower rotor
gears, from entering the rotor compartment. Former blowers used a ring-type oil seal consisting of a fiber
washer, O-ring, retainer, and seal spring in each end of the blower rotors.
Figure 1. Blower Mounting
Inspect Blower (Attached to Engine)
The blower may be inspected without removing it from the engine. However, the air cleaner and the air inlet
housing must be removed.
When inspecting the blower with the engine running, keep your fingers and clothing away from the
moving parts of the blower and run the engine at low speeds only.
Dirt or chips drawn through the blower will make deep scratches in the rotors and housing. Burrs around such
abrasions may cause interference between the rotors or between the rotors and the blower housing.
Leaky oil seals are usually indicated by the presence of oil on the blower rotors or inside surfaces of the blower
housing. Run the engine at low speed and direct a light into the rotor compartment and toward the end plates
and the oil seals. A thin film of oil radiating away from a seal indicates an oil leak.
A worn blower drive resulting in a loose, rattling sound within the blower may be detected by running the engine
at approximately 500 rpm.
Loose rotor shafts or worn rotor shaft bearing surfaces will result in contact between the rotor lobes, the rotors
and the end plates, or the rotors and the housing.