CYLINDER HEAD VOLUME TESTS
CYLINDER HEAD VOLUME
(Squish-Gap Method)
To check the squish gap, a micrometer and a heavy
piece of solder will be needed.
1. Remove the spark plugs from the engine.
2. Insert the solder piece down through the spark
plug hole and push it up against the inner
cylinder bore towards the MAG-side of the
engine.
3. Pull the recoil rope and crank the engine over
several times while the solder is being held
firmly in place.
4. Remove the solder from the cylinder. Using the
micrometer, measure the very end of the
squeezed solder piece. Record the reading.
NOTE: If the solder hasn’t been squeezed by the
piston, a larger piece of solder must be used.
Repeat procedure.
5. Using the opposite end of the solder piece, insert
it down through the spark plug hole towards the
PTO-side of the engine. Push on the solder until
it contacts the inner cylinder bore.
6. Pull the recoil rope and crank the engine over
several times. Remove the solder from the
cylinder and measure the squeezed end with a
micrometer. Record reading and refer to the
chart.
NOTE: Measure from PTO to MAG-side of the
piston to accurately measure the squish gap.
Never measure across piston, exhaust to
carburetor side, as the piston will rock and the
reading won’t be accurate.
Readings may vary from side to side. Make sure the
smaller reading is within the specifications listed.
CYLINDER HEAD VOLUME
(CYLINDER HEAD
INSTALLED METHOD)
To check the cc volume, a measuring tool called a buret
will be needed. It is capable of measuring a liquid in
cc volumes.
1. Fill buret with 10W engine oil.
2. Remove the spark plugs from the cylinders.
3. Run piston up to TDC (Top Dead Center).
4. Insert buret into spark plug hole and open buret
valve. Run oil into the spark plug hole until it
reaches the top of the spark plug hole. Turn off
the buret valve.
5. Check the buret scale to see how much oil has
been used to fill the combustion chamber. From
the total amount, subtract 2.2 cc. Compare the
findings with the chart.
NOTE: The above procedure will work fine on a
new engine. Engines with many hours of use, may
require a small change in the procedure. In step 3,
remove the cylinder head. Wipe a small amount of
heavy grease around the outer diameter of the
piston to seal space between the piston and
cylinder bore. Replace head and tighten to
specification; then continue with steps 4 and 5.
CYLINDER HEAD VOLUME
(FLAT PLATE METHOD
)
The third method of checking for proper combustion
chamber volume will require a 1/8 in. or 3/16 in. thick
piece of plexiglass, some heavy grease, and a buret.
The plexiglass piece must be flat and also large enough
to cover the entire gasket surface of the cylinder head.
Using a 3/16 in. drill bit, drill two holes through the
plexiglass piece. Locate the holes one inch apart inside
the combustion chamber area (towards center of
piece).
1. Remove the cylinder head from the engine.
Clean all carbon from the combustion chamber
area.
2. Position the cylinder head squarely in a vise with
its gasket surface up. Leave the spark plug in
place and grip the metal portion of the spark plug
for holding the cylinder head.
3. Apply a light coat of grease to the gasket surface
of the head. Squeeze the piece of plexiglass
firmly down onto the gasket surface. The grease
will act as a sealant between the two pieces.
4. Using a buret filled with light oil, fill the
combustion chamber through either of the two
holes drilled in the plexiglass. Continue to fill
the combustion chamber until the fluid appears
at the bottom of the second hole. Stop filling
procedure and take a reading off the buret as to
how much fluid was used. The specification
found in the chart includes the spark plug
volume, so there won’t be any need to subtract
from the reading.
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