Engine Cannot Be Cranked Nor Barred Over
15-5. Most pre-starting instructions for large engines specify that the crankshaft should be turned one or more
revolutions before starting power is applied. If the crankshaft cannot be turned over, check the turning gear to
be sure that it is properly engaged. If the turning gear is properly engaged and the crankshaft still fails to turn
over, check to see whether the cylinder test (relief) valves or indicator valves are closed and are holding water
or oil in the cylinder. When the turning gear operates properly and the cylinder test valves are open but the
engine nevertheless cannot be cranked or barred over, the source of the trouble is probably of a serious nature.
A piston or other part may be seized or a bearing may be fitting too tightly. Sometimes the difficulty cannot be
remedied except by removing a part or an assembly. Some engines have ports through which pistons can be
inspected. If inspection reveals that the piston is defective, the assembly must be removed. Figure 15-1 shows
the testing for stuck piston rings through the scavenging-air distributor manifold port. If the condition of an
engine without cylinder ports indicates that a piston inspection is required, the whole assembly must be taken
out of the cylinder. Engine bearings have to be carefully fitted or installed according to the manufacturer’s
instructions. When an engine cannot be jacked over because of an improperly fitted bearing, someone probably
failed to follow instructions when the unit was being reassembled.