Oil seal leaks in diesel engines of walk-behind or small four-wheeled tractors are common, and the causes are numerous and complex. The main causes are as follows: ① A stuck oil level indicator, causing excessively high oil pressure; ② A malfunctioning negative pressure (valve) pipe, causing excessively high crankcase pressure; ③ Excessively high oil pump outlet pressure and flow rate; ④ Poor quality of the oil seal lip or improper repair and installation methods.
If the cause is ① or ②, the oil level indicator or negative pressure (valve) pipe can be repaired. If the cause is ③, a gasket must be added between the oil pump and the pump cover to restore normal outlet pressure. However, this cause is uncommon in new vehicles because the oil pump outlet pressure is already determined at the factory. If the cause is ④, the following checks must be performed:
1. Check if the oil seal lip is installed in the wrong direction. Oil seals seal lubricating oil, but the sealing function of the oil seal lip can only seal one direction to prevent leakage, not the other. Therefore, even the best quality oil seal will leak if installed backwards. During installation, ensure the lip faces inwards; that is, the side with the trademark should face outwards.
2. Check if the oil seal spring is outside the spring groove. The function of the oil seal spring is to apply radial pressure to the lip, tightening it against the shaft to ensure the sealing of the lubricating oil. If the spring is outside the groove, the oil seal will obviously lose its sealing function and leak.
3. Keep the area around the oil seal lip that contacts the shaft clean. Iron filings, dust, and other debris at the contact point between the oil seal lip and the shaft can cause premature wear of both the lip and the shaft, and may even scratch the lip, leading to leakage. Therefore, cleanliness is crucial during installation and use. Replace the oil seal if any wear or scratches are found on the lip, even minor ones.
4. Maintain the integrity of the oil seal lip. Prevent scratches on the lip; even minor scratches or cracks can cause serious oil seal leaks. Because the inner hole of the oil seal is smaller than that of the journal, the lip of the oil seal will be stretched when it is installed, and it is easily scratched by the keyway, hole, chamfer, burr and flash on the shaft.
