+Figure 3-51. Valve Rotators.
roller link chain may have a single or a double row of
slipping on the sprockets, provide more precise
valve timing, and compensate for component stretch
and wear. Engines with belt-drive configuratlons
(3) Belt Drive (C, Fig. 3-53). Sprockets on the crankshaft
usually use a spring-loaded idler wheel. Chain-
and the camshaft are linked by a continuous neoprene
driven configurations usually use a fiber rubbing
belt. The belt has square-shaped Internal teeth that
block that Is either spring loaded or hydraulic. The
mesh with teeth on the sprockets. The timing belt is
hydraulic tensioner Is a device that works by the
reinforced with nylon or fiberglass to give It strength and
same principle as a hydraulic lifter (para 3-13h(2)).
prevent stretching. This drive configuration Is limited to
The hydraulic tensioner Is much more desirable for
overhead camshaft engines.
use with a rubbing block because it takes up the
slack in the chain without exerting excessive
e. Timing Belt and Chain Tensioners (Fig. 3-53). Most
pressure, resulting in longer component life.
engines with chain-driven and all engines with belt-
Timing Marks (Fig. 3-53) The camshaft and the
driven camshafts employ a tensioner. The tensioner
crankshaft always must remain In the same relative
pushes against the belt or chain to keep It tight. This
position to each other. Because the
Figure 3-52. Camshaft Support.