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SECTION II DIeSeL eNGINe FUNDaMeNtaLS
Rocker Lever
Valve Spring Poppet Valve Valve Guide
Valve Port
Cylinder Head
Push Tube
Roller-Type Cam Follower
Piston
FIGURE 6-17 Cam Shaft
FIGURE 6-16
A gear train mounted on the front of an
engine block.
Typical parts of a simple valve train mechanism.
Tensioner Tensioner
Gear Drive FIGURE 6-18
Chain Drive
Belt Drive
Three common types of valve train mechanisms (gear, chain, and belt drive) are used on diesel engines.
levers, and bridges FIGURE 6-16 . In overhead camshaft engines, the camshaft is located in the cylinder head. While there is a reduction of parts and complexity to the valve train mechanism associated with overhead camshaft engines, they are used primarily to enable higher pressurization of fuel by injectors, which can directly contact an injector lobe on the camshaft.
Valve and Gear Train Mechanism A gear train or valve timing mechanism is used to coordinate the movement of the crankshaft with the camshaft and the valves.
The gear train may also operate fuel injection apparatus, lubrication, power steering, and coolant pumps, accessory drive mechanisms, and even power take-off (PTO) pumps FIGURE 6-17 . Belts, chains, or gears are typical components used to transfer power in the gear train FIGURE 6-18 . The stronger, more durable gear-type valve train mechanism is used on most commercial diesel vehicles. This strength is required because firing impulses accelerate the crankshaft much faster, and high compression forces momentarily slow the engine, which increases stress on the valve train mechanism. A thrust washer between the engine block and rotating cam gear prevents the cam gear from wearing
FOR SAMPLE PURPOSES ONLY. NOT ALL CONTENT IS FINAL 9781449624118_CH06_Pass02.indd 176
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