How to diagnose a single-cylinder diesel engine that cannot start?

Due to the high combustion pressure and noise of diesel engines, cylinder head gasket erosion is difficult to detect and diagnose, leading to delayed replacement of the gasket. This results in cylinder liner deformation, damage to the water seal ring, and severe erosion grooves caused by the impact of high-temperature and high-pressure gas at the crossbeam between the cylinder head and cylinder block. This makes repair difficult and parts may become unusable, seriously affecting the fuel economy of the diesel engine. If the diesel engine cannot be started or is difficult to start when the crankshaft is turned at high speed using a hand crank, it indicates a starting problem. The main causes of starting difficulties are faults in the fuel system or compression system.

1. Causes of the Fault

(1) Fuel system faults: These mainly include no fuel in the tank or the fuel tank switch not being opened; cracked or dented fuel tank; blocked vent hole in the fuel tank cap; air in the fuel system; and the diesel filter being blocked by impurities or dirt. High diesel viscosity and low ambient temperature reduce diesel fluidity. Diesel fuel is contaminated with water, resulting in ineffective combustion, difficulty starting the diesel engine, and blockage of the combustion chamber insert's starting orifice by carbon deposits. Incorrect fuel injection advance angle and severe wear of the camshaft cam reduce fuel supply. Severe wear of the delivery valve assembly, damaged or leaking delivery valve gaskets. Severe wear of the plunger assembly causes low fuel pressure. The plunger is stuck in the plunger sleeve; the plunger inlet is blocked; the plunger adjusting head has slipped out of the speed control lever slot and is in the no-fuel-supply position, causing no fuel supply. The plunger spring or delivery valve spring has weakened or broken. Severe wear of the injector assembly results in low injection pressure, poor atomization, dripping, excessive return fuel, injection deviation, and an unacceptable spray cone angle. The injector pressure regulating spring has weakened or broken. A leaky high-pressure fuel line joint causes severe fuel leakage.

(2) Compression and valve train malfunctions: Malfunctions related to the compression and valve train mainly include severe deformation of the engine block and cylinder head; aging, deformation, or substandard manufacturing of the cylinder head gasket; excessively high or low bolt tightening torque, resulting in poor sealing and air leakage; severe wear of cylinder liners, pistons, and piston rings; excessive cylinder clearance; increased piston ring edge clearance; piston ring opening rotation; excessive opening clearance; piston ring coking or seizure, causing cylinder leakage; weakened or broken valve spring force; severe carbon buildup, burning, or wear on intake and exhaust valves, causing valve leakage; excessively small intake and exhaust valve clearance, resulting in incomplete valve closure; worn valve lock clips and valve spring seats; bent, broken, or detached valve pushrods; severe wear of the camshaft intake and exhaust cams, resulting in insufficient intake and incomplete exhaust; clogged air filter or exhaust pipe; incorrect installation of timing gears or misaligned markings, causing incorrect valve timing. Overly tight pressure relief valve adjustment can lead to incomplete valve closure and air leakage, as well as cracks in the engine block and cylinder liners, allowing coolant to enter the cylinders. Worn crankshaft journals, connecting rod bearings, or severely worn intake and exhaust valves with increased sagging can also reduce the compression ratio.