NBR motorcycle oil seals.Lip seals retain the oil inside the airend while keeping air, dust and dirt from entering along the rotating shaft when the machine is off load. Remember, when the inlet valve closes and the airend continues to rotate, a vacuum
may be pulled on the inlet end.
Some lip seals are made of a high nitrile Buna N or Viton rubber encased in steel and were designed to withstand only a few pounds of back pressure. Compressors with these lip seals rely on airend discharge valves, oil stop valves and a fast acting sump blow down valve to prevent the system
pressure from slipping back up through stopped rotors and pressurizing the drive side of the airend.NBR motorcycle oil seals.
Rubber lip seals can not withstand high pressures. A leaky seal of this type may be an indicator of a bad airend check valve or oil stop valve which will allow full discharge pressure to reach the seal.
The newer style of lip seals use Teflon (trademark). These are much stiffer and can withstand high pressure as well as synthetic compressor oils.NBR motorcycle oil seals.
In general, lip seals are more sensitive, than mechanical seals, to shaft runout and surface irregularities. A lip seal will often leak oil if the shaft has a total indicated runout of more than only a few thousands of an inch.
You can not assume that because the shaft runs true when spun by hand that it will do so at speed. Therefore, it is even more important that you check the radial or side play in the shaft before replacing a leaking lip seal.NBR motorcycle oil seals.
An out of balance coupling or drive belt pulley will cause shaft runout in an airend with a worn bearing. Tight belts will also pull the shaft away from the original center line as bearing wear increases. This puts all excess clearance on one side of the seal.
You should isolate the machine and loosen the belts or coupling. Then, push the shaft back and forth while measuring shaft deflection with a dial indicator to check for bearing wear.NBR motorcycle oil seals.
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