Causes and inspections of high pressure in the crankcase of outboard motors

The fault of high crankcase pressure of marine engine is a relatively common fault during the operation of the engine. According to the manufacturer of outboard motors, before this fault occurs, it is necessary to understand the cause of this phenomenon and check it:
1) According to the fault phenomenon, determine whether it is a high crankcase pressure fault of the engine. The specific performance of the fault is as follows:
1. The engine smokes;
2. The engine is weak;
3. A large amount of engine oil is sprayed out from the crankcase breather port or oil dipstick;
4. Large oil consumption.
2) Analyze the reasons for different failure phenomena:
1. The air compressor is damaged, and the piston ring and cylinder liner of the air pump will also have the same wear failure as the engine piston ring and cylinder liner, causing high crankcase pressure;
2. The supercharger is damaged, and the service personnel often ignore that the damage to the supercharger will also cause large exhaust. The oil seal of the supercharger seals the high-pressure gas to prevent it from entering the oil chamber of the supercharger. If the oil seal of the supercharger is damaged, there may be high crankcase pressure;
3. Caused by the gas distribution mechanism;
4. The wear of the valve, seat ring and conduit of the gas distribution mechanism will inevitably increase the fit clearance, cause the oil to mix into the combustion chamber, and may also cause high-pressure gas to enter the crankcase of the cylinder block, resulting in high crankcase pressure;
5. The counterpart of the piston ring is worn or damaged. The piston has two air rings. If it is damaged, matched or worn, it may also cause high-pressure gas to enter the crankcase of the cylinder block, resulting in large exhaust and high crankcase pressure;
6. The cylinder liner is worn, and the wear of the cylinder liner can also cause high-pressure gas to enter the crankcase of the cylinder block, resulting in large lower exhaust;
7. Too much engine oil is added. Too much engine oil can also cause high crankcase pressure, causing a large amount of engine oil to be ejected from the lower exhaust port.
3) Troubleshooting process:
1. Understand the recent operating conditions and maintenance status of the engine. Dust is one of the main causes of engine early wear and tear, and checking the air system is the main job; check for high temperature history. High water temperature will also cause high temperature wear of the engine;
2. Check the oil quality and oil replacement cycle; check the supercharger to see if there is any oil leakage or the shaft clearance is too large;
3. Then the engine cylinder head can be removed to check the cylinder head, piston and cylinder liner.