Most oil seal failures begin at installation. A folded lip, a scratch from the shaft keyway, installation at an angle, or seating that is not flush, any of these create a leak path that cannot be corrected without replacing the seal again. Correct installation takes less than five minutes. Incorrect installation wastes the seal.
Step 1, Inspect Before Installing
- Check the new seal is the correct size, bore, OD and width
- Inspect the lip for any nicks, cuts or deformation in the packaging
- Check the garter spring is correctly seated in the groove around the primary lip, a dislodged spring means zero sealing force
- Inspect the shaft surface in the seal contact zone, smooth ground finish required (Ra 0.2, 0.8 µm). Any rust, pitting or visible machining grooves will cut the new lip
- Inspect the housing bore for damage or corrosion, a damaged bore means the seal OD cannot seal against the housing
Step 2, Prepare the Shaft
The biggest risk during installation is lip damage when sliding the seal over the shaft. Any sharp edges cut the rubber lip immediately.
- Remove all burrs from keyways and threads with a fine file and emery cloth
- Cover keyways, threads and splines with a thin stainless steel cone or sleeve (installation tool) before sliding the seal over. Many seal suppliers provide these. Improvise with thin sheet metal or card wrapped around the shaft.
- Apply a thin film of clean lubricant (the same oil that will be sealed, or assembly grease) to the shaft contact zone and to the seal lip, this prevents the rubber running dry for the first seconds of rotation
- Do NOT use petroleum jelly (Vaseline) on FKM (Viton) seals, it causes swelling. Use the process lubricant or silicone grease.
Step 3, Press the Seal Into the Housing
The seal must be pressed in squarely, evenly, and only as far as the correct seated depth. Do not hammer on the seal face directly.
- Use a seal driver or a flat press plate that contacts the metal case of the seal evenly around its circumference, not a drift on one side of the seal
- Press the seal in until it is flush with the housing face, or 1, 2mm below flush if the design requires it
- Apply light lubricant to the OD of the seal before pressing into the bore, this reduces the risk of the housing bore scraping the rubber OD on entry
- If you only have a hammer and a socket: use the socket as an even driver, contact only the metal case. Never hit a rubber-covered OD seal directly with a hammer.
Step 4, Check Orientation
The primary sealing lip must face toward the lubricant (inward). The dust lip (on TC type) faces outward. Installing a TC seal backwards means the primary lip faces the wrong way, it will not retain oil and will allow contamination past the dust lip, which is now acting as the only barrier.
Standard rule: the spring (garter spring) side of the seal faces the oil side.
Step 5, Shaft Assembly
When assembling the shaft back through the installed seal, use the same protection sleeve used during seal installation, again protecting the lip from keyways and threads. Slide slowly. Never force or rotate the shaft quickly through the seal before final assembly is complete.
Post-Installation Checks
| Check | How | Acceptable Result |
|---|---|---|
| Seal flush with housing | Straight edge across housing face | Flush or 1, 2mm below |
| Lip not folded | Visual, shine a torch behind the shaft | Lip makes even contact around shaft |
| No gap under OD | Visual inspection of housing bore edge | No visible gap around seal OD |
| First hour run | Observe for immediate leakage | No visible oil at seal face after 1 hour warm-up |
What to Do If the Seal Leaks After Installation
A correctly installed seal in a correct housing with a correct shaft should not leak. If it does within the first 24 hours:
- Check if the shaft finish is damaged, replace shaft if worn groove exists in the seal contact zone
- Check if the seal was installed at an angle, remove and reinstall squarely
- Check if the housing bore is oversized, if so, use a liquid sealant on the OD at next installation or replace the housing
- Check if the garter spring came off the lip during assembly, remove and replace the seal