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Tracking Down Engine Leaks
Anywhere you look on the farm, you will find seals of different designs. The purpose of any seal is to keep a fluid from leaking out and, equally as important, foreign material from entering. The ability to isolate the component from external influences is just as imperative as keeping the fluid inside. This needs to be understood since most of us only consider a seal failed when there are visible signs of leakage. A seal employed in a vacuum pump, if weakened, will introduce dirt and decrease the pump’s operation and useful life without any visible signs.
Though commonly identified as a lip seal, it also goes by the name rotary or shaft seal. On an engine, you will find lip seals in use at the front and rear of the crankshaft (one-piece rear main seal), in hydraulic pumps, in a water pump, and other areas. On a vehicle or machine, lip seals are employed when there is a need to isolate two sides of a component within a rotating member.
The lip seal has an edge that rides on the rotating part while allowing a film of the fluid to reside between the lip and the shaft. The confluence of the fluid film and the sealing material (usually some family of rubber or hybrid material such as PTFE) causes a hydrodynamic action. In addition, a weak but effective pumping action takes place that further enhances the seal’s ability. As the seal ages, not only does the lip that contacts the shaft wear but also the material it is made from becomes brittle and less pliable. Thermal excursions may give it the tendency to bow away from the rotating member, too. When any of this occurs, the seal becomes challenged and can leak both ways.
When changing a lip seal, it is imperative that it is made from the proper material for the fluid that is going to be isolated. Also, rpm of the shaft (the higher the speed, the greater the heat generated at the contact point) must be considered. Many lip seals are directional in nature, especially those used in engines. The seal will usually have a small arrow on it to identify the rotation required for the lip to make contact on the shaft. If installed in the wrong rotation, the seal will leak immediately.
The cavity the seal resides in needs to be extremely clean and free of any rust or corrosion. If the seal is even minutely cocked, it will not function. The shaft that runs through it must also be clean and smooth and possess no axial grooves. If there are any grooves, they can work like an auger and pull fluid past the lip.
It’s important not to damage the lip seal when it’s being pressed or tapped into place. Though there are dedicated seal installers, you may be tempted to improvise and use a socket from a ratchet set. If common sense is employed and the seal and socket can interface properly, this is an acceptable procedure.If you’re careless, however, or the fit is compromised, then the repair may be for naught. A lip seal installation kit with a variety of proper sizes may be a worthwhile investment. Always lightly lubricate the cavity the seal fits into before attempting installation.
Common mistakes made when servicing any lip seal include the following:
- Not lubricating the shaft, so the lip runs dry on the rotating member before it can pull a film of liquid.
- Reusing even a fairly new lip seal.
- Buying a cheap imported seal that has the proper outside diameter but is made from the wrong material.
Most lip seals are designed so that once removed, they can’t be put back into service. This is especially true on a component that spins at high speed and is exposed to high temperatures. You may get lucky every now and then, but do not make it a habit.
If you follow these simple steps and invest in the proper name brand lip seals, you’ll be rewarded with a job well done and a long-lasting repair.