Page 8 - E BOOK ENGINE MECHANICAL M2

1. TECHNICAL FEATURES OF 4B1 ENGINE

(7) Valve Train
The valve train is the 4-valve, double
overhead camshaft (DOHC) type in
which the camshafts are located
above the valves. Two inlet and ex-
haust valves for each cylinder are
arranged in a V shape.
A valve tappet is interposed between
the camshaft and each valve, which
allows the valves to be opened and
closed directly by the camshafts.

Fig. 1-8

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◆ Valve mechanism
Figure 1-9 shows the cylinder head that was used on
the 4G63DOHC-16 valves engine. The design of the
cylinder head had the following features.
(1) The valves are arranged to form a letter V. Two in-
take valves and two exhaust valves are provided for
each cylinder. These valves are indirectly operated by
the intake and exhaust camshafts through the rocker
arms.
Fig. 1-9

(2) The rocker arms are of the roller type, in which a roller with needle bearings is installed on the
portion in contact with the cam. This type of rocker arm reduces friction loss of the valve train in the
DOHC arrangement to a minimum.
(3) The hydraulic type lash adjusters automatically adjust the valve clearance, minimizing noise gen-
erated by the valve train. They also eliminate the need for valve clearance adjustment.
(4) The valve springs, whose cross section is oval, contribute to the enhanced spring load. This in
turn ensures that the valves operate properly, especially at high speed.

◆ Lash adjuster
The hydraulic lash adjuster is of the end pivot type. It
eliminates the need for adjustment of the valve clear-
ance. There are four lash adjusters provided for each
cylinder for a total of 16 in all.

Fig. 1-10

Pub. No. PTAE1225 1 - 5