- Another important consideration is the compatibility of the main bearing oil seal with the engine's oil. The seal must be designed to withstand the chemical properties of the oil, such as its viscosity and additives, without deteriorating. Using the wrong type of oil can cause the seal to fail prematurely. Therefore, it is essential to use the recommended oil type for your engine to ensure the longevity and reliability of the main bearing oil seal.
The other way oil seals work is by stopping outboard materials that can damage the machine or contaminate its lubricant. The outboard materials that the oil seal will need to stop depend on the application. However, the most common kinds are dirt, moisture, and the particles produced during manufacturing.
Manufacturing and Quality Control

As shown in Figure 1, sealing devices come in two types: contact and non-contact.
Oil seals are among the major contact type sealing devices.
In this an auxiliary lip is provided along with the regular sealing lip. The additional dust lip protects the main sealing lip against dust and other fine solid contaminants and therefore this type is recommended for use in polluted environments. To achieve a long lifetime a suitable lubricant between the two sealing lips should be applied.
There is a British Standard laid down for the control of synthetic rubbers. BS 3574 (1989) helps to determine shelf life – for instance, Nitrile (NBR) and Polyacrylic (ACM) are Group ‘B’ rubbers and have a 7-year life, whilst Silicone (VMQ) and Fluoroelastomers (Viton®) are Group ‘C’ rubbers and have a 10-year shelf life. PTFE and Leather do not come into this category but like the others should be kept in the original packing for as long as possible away from direct light, dust, and humidity. Ozone, which can also be produced by battery-driven forklift trucks has a very bad effect on synthetic rubbers. Finally, protect the sealing lip – DO NOT hang the seals on nails, wire etc.

Most conventional oil seals are designed only to withstand very low-pressure applications (about 8 psi or less). If additional internal pressure is present or anticipated, pressure relief is necessary.