When you start the lawn mower engine, you can find that the crankshaft can rotate normally when you press the starting switch, but the engine itself cannot start and run, there is no smoke discharged from the exhaust pipe at the same time, and there is no explosion sound in the engine cylinder, such a fault situation generally belongs to the oil circuit problem of the engine, and we will carry out a detailed and specific analysis on the various causes of this fault as follows.

The first reason is that there is no oil in the fuel tank. This is the most basic and the easiest to ignore cause of the fault. If there is no fuel in the fuel tank of the lawn mower at all, the engine cannot get the fuel required for combustion and work, so even if the crankshaft can rotate normally driven by the starter, the engine will not have the conditions for ignition and starting, and there will naturally be no oil fumes or smoke discharged from the exhaust pipe, which is the simplest cause of this kind of fault.

The second reason is that the fuel filter and the water-oil separator are blocked. The fuel filter is used to filter out the impurities and dirt mixed in the fuel, and the water-oil separator is used to separate the moisture from the diesel oil. After the lawn mower has been used for a long time, a lot of impurities will accumulate inside the fuel filter and block the filter completely, and too much water and sundries will also block the inside of the water-oil separator. This kind of situation will make the fuel unable to flow through the filter and the separator smoothly, and the engine can’t get normal and stable fuel supply. So the engine can only rotate but cannot start, and there is no smoke coming out from the exhaust pipe.

The third reason is that the low-pressure oil circuit cannot supply oil. The low-pressure oil circuit is responsible for transporting the fuel from the fuel tank to the fuel injection pump continuously. If the low-pressure oil pipeline is broken, cracked or the joint is loose and not sealed well, a lot of air will enter the oil circuit, and the fuel will leak out from the damaged parts at the same time. This will cause the fuel delivery pump to be unable to suck up the fuel normally, and the engine can’t get the fuel needed for combustion and operation. This problem directly leads to the result that the engine cannot start and there is no smoke in the exhaust pipe.

The fourth reason is that the fuel injection pump cannot pump oil. The fuel injection pump is the core component of the engine fuel supply system, which is responsible for pressing the fuel into the engine cylinder at a high pressure, and if the internal parts of the fuel injection pump are worn, stuck or damaged, the fuel injection pump will lose the function of pumping oil, so that no fuel can enter the engine cylinder, the engine has no way to carry out combustion work, and there will be no smoke discharged from the exhaust pipe.

The fifth reason is that there is air in the oil circuit. Air will enter the engine oil circuit in many cases, such as when the fuel tank is used up, the pipeline joint is loose, or when the fuel filter is replaced, the air entering the oil circuit will form air resistance, which will block the normal flow of fuel, make the fuel injection pump suck air instead of fuel, so that the engine cannot get fuel supply, and naturally cannot start and produce exhaust smoke.

The sixth reason is that the valve timing is out of alignment. This is a mechanical fault that affects the starting of the engine, the opening and closing time of the engine valves must be coordinated with the stroke of the piston in the cylinder, and if the valve timing is wrong, the opening time of the valves will be inconsistent with the movement of the piston. For example, when the piston is in the compression stroke of the cylinder, the intake and exhaust valves are open, the fresh air and fuel mixture will be pushed out of the cylinder, so that there is no combustible gas in the cylinder to burn, and the engine cannot start and has no exhaust smoke.

The seventh reason is that the solenoid valve of the fuel injection pump is broken and in the closed state. The solenoid valve on the fuel injection pump of many diesel lawn mowers is used to control the on-off of the fuel entering the high-pressure chamber, and if the solenoid valve is damaged and fails, it will always be in the closed state, so that the diesel fuel cannot enter the high-pressure chamber of the fuel injection pump, the fuel injection pump cannot spray oil normally, and the engine will not have the conditions for ignition starting, and there will be no smoke from the exhaust pipe.

In the actual maintenance and inspection of the lawn mower, when we encounter the fault that the crankshaft can rotate but the engine cannot start and there is no smoke from the exhaust pipe, we should check the seven reasons one by one in the order from simple to complex, first check the most basic fuel tank oil quantity, then check the blockage of the filter and the oil supply of the low-pressure oil circuit, then check the fuel injection pump and the air in the oil circuit, and finally check the valve timing and the solenoid valve of the fuel injection pump. Most of these faults can be solved by simple operations such as adding fuel, cleaning or replacing the filter, draining air from the oil circuit, and replacing damaged parts, which can make the lawn mower return to normal starting and working state quickly.