900 S Coupe L4-1985cc 2.0L DOHC Turbo EFI (1998)
Balance Shaft Chain: Description and Operation
The balance shafts are driven by a chain and rotate at twice the crankshaft speed.
A special idler sprocket over which the chain passes causes the balance shaft on the exhaust side to rotate in the opposite direction to the other balance
shaft. The chain is located by two fixed chain guides and a pivoted chain guide on which a chain tensioner acts.
When the engine is running, pressurized engine oil acts on the chain tensioner in the opposite direction to control the force applied to the chain and so
reduce both chain wear and chain noise to a minimum.
Both the balance-shaft sprockets and the idler sprocket incorporate thrust rings to reduce chain noise still further.
The thrust rings absorb the force of the chain where it engages the sprocket teeth, ensuring smoother operation and quieter running.
Due to the smaller surface contact angle, the thrust rings on the exhaust side are larger than those on the inlet side.
