Service Manual

COMPRESSION 6-1
Section 6
COMPRESSION
COMPRESSION CHECK
Before measuring compression pressure;
Check cyl. head to torque.
Be sure battery is fully
charged on electric starter models. Start engine
and allow
it to warm up. During warm up, check
for leaks around cyl. head gasket. Stop engine.
1. Remove spark plug and screws compression
gauge into the plug hole securely.
2. Crank engine with recoil or electric starting for
several seconds and take highest pressure gauge
reading. Cylinder compression should not
be
less than 3 kg/cm² (43 psi).
3. If compression reading is too high, check for
carbon built up in combustion chamber.
Carbon deposits in combustion chamber
should be removed every
100 to 200 hours
of. use, or whenever cyl. head is removed.
4. If the compression pressure is less than spe-
cified,
it is usually the result of one or more of:
Leaking cyl. head gasket.
Warped cyl. head.
Worn piston rings.
Damaged piston.
Worn cyl. bore.
Burned or warped
valves.
Improper valve clearance.
Broken
valve springs.
To a great extent, compression can also be
practically measured by:
Disconnect spark plug cap to
prevent engine starting during compression
test.
Be careful not to get your fingers caught in fly-
wheel fins during
test.
Spin flywheel counter clockwise (flywheel side)
against the compression stroke;
a sharp rebound
indicates satisfactory compression. Slight or
no rebound indicates poor compression.
CYLINDER HEAD AND
HEAD GASKET REMOVAL
CAUTION: Always note the position of each
cyl. head screw
so they may be properly reassem-
bled.
torque and maintain positive sealing of the com-
bustion chamber.
1. Remove cyl. head and gasket.
*-
CYLINDER HEAD TIGHTENING
PROCEDURE
CAUTION: Do not use a sealer of any kind on gas-
ket.
1. Coat head bolts threads with a light film of
2. Tighten screws down evenly by hand.
3. Use a torque wrench and tighten head bolts
in the sequence
as shown, and to the specified
torque.
oil and install the bolts.
Cylinder Head Tightening Torque
L
34 to 39 N-m (25 to 29 ft-lbs)
CAUTION: Do not turn one screw down com-
pletely before the others,
as it may cause a warped
cyl. head.
A FB46OV has 3-heat-resistant high-tension studs
in the exhaust
valve side area to prevent loss of