The purpose of a front crankshaft oil seal is to seal the crankcase and prevent oil leakage.

Possible reasons of oil leakage of a crankshaft oil seal:

1. Non-petroleum-based lubricant is not used:

If non-petroleum-based lubricant is not used during press fitting of the crankshaft oil seal, the oil seal may become loose or even fall off after operation of the engine for some time.

2. Improper installation:

If the parallelism between the press fitting surface of the rear oil seal and the installation surface of the rear oil seal seat fails to meet the technical requirement of the assembly drawing, the rear oil seal lip may deform due to uneven force. As a result, after the engine is used for some time, the oil seal lip or even the entire oil seal may get twisted, causing damage to the oil seal and oil leakage.

3. Used for an extended period of time:

If the engine has been used for long, cracks may develop at the naturally aged lip of the oil seal, thus leading to oil leakage.