19-2
2. CHAIN DRIVE CAM DRIVE SYSTEM
STRUCTURE AND FEATURES
The intake/exhaust cam drive method was changed from the existing cogged belt drive to the silent chain drive type.
The chain tensioner was changed to the hydraulic type to make it maintenance free.
Structure:
As the basic structure of this chain drive cam drive system, the balancer is laid out in front of the crankshaft and the drive
valve system is laid out behind the crankshaft.
• The balancer and intake/exhaust cam drive were changed from the two-cogged belt type (BF115A•130A) to the two-
silent chain type.
• Cam chain tension adjustment was changed from the existing manual adjustment with spring to the automatic
adjustment by drawing the main gallery oil pressure. This system is the same in structure as the system adopted on
car.
• As the unique feature of these outboard motors, the dedicated chain lubrication oil jets are provided on the crankshaft
sprocket, intake/exhaust camshaft sprocket and the driven sprocket. These oil jets feature the unique rib shape to collect
the lubrication oil around the respective sprockets.
Effects:
• The chain guide is provided regulating 80% or more of the chain line. It thereby regulates deflection of the chain and
eliminates wind noise of the chain.
• The existing spring type chain tensioner needs chain tension adjustment regularly (when chain sound was produced).
These outboard motors are equipped on the hydraulic tensioner that has the adjustment mechanism (one-way lock
mechanism) to maintain constant chain tension by means of the hydraulic pressure. It also adopted the unique
lubrication system. Maintenance free during the service life of the chain tension was realized by adoption of these new
features.
INTAKE CAMSHAFT
SPROCKET
EXHAUST CAMSHAFT
SPROCKET
HYDRAULIC CHAIN
TENSIONER
CRANKSHAFT
SPROCKET
DRIVEN SPROCKET
OIL JET