Troubleshooting
8-19
c. Check that the TDC marks are still aligned as described in Step7, If not,
turn the crankshaft as required, then relock the holding tool in position.
9. Perform a cylinder leak down test by applying air pressure to the combustion
chamber. Follow the manufacturer’s instructions while reading the percent of
leakage on the gauge. Listen for air leaking while noting the following:
Note:
Because of play in the transmission gears, it is unlikely the engine will stay at
TDC on the first try If the crankshaft turns, reposition the countershaft slightly
and then relock it in position with the holding tool. After several attempts, you
will get a feel of the transmission play and know what direction the countershaft
should be turned and locked.
If a large amount of air escapes from the exhaust pipe or through the throttle, the
air is leaking through on open valve, Check the index mark to make sure the
engine is at TDC on the compression stroke, If the engine is remaining at TDC but
there is still a large amount of air escaping from the engine, the crankshaft is off
one revolution. Turn the engine 360°and realign the TDC mark as described in
Step 7, then relock it as described in Step8.
a. Air leaking through the exhaust pipe indicates a leaking exhaust valve.
b. Air leaking through the throttle indicates a leaking intake valve.
c. Air leaking through both the intake and exhaust valves indicates the engine is not set
at TDC on its compression stroke.
d. Air leaking through the coolant filler neck indicates a leaking cylinder head gasket or
a cracked cylinder head or cylinder liner.
e. Air leaking through the oil filler hole indicates the rings are not sealing properly in the
bore.
11. If the cylinder leak down is 10 percent or higher, further service is required.
12. Disconnect the test equipment and install all the parts previously removed.
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