JT8D Bearings & Seals
The main bearings support and align the two rotating systems, N1 N2. They are antifrictional types to reduce rolling friction. They are lubricated, cooled and cleaned by the oil. Some bearings may be vibration damped by the oil.
Roller bearings support rotating parts radially, absorbing angular loads, they do not prevent axial movement. All rollers have a one piece cage, a ring with a recess, a ring without a recess, either the inner or outer ring of a bearing may be the recess ring.
Ball bearings hold rotating parts in axial and radial alignment. They absorb both thrust (axial) and angular loads. All ball bearings have a one piece cage, two rings (inner and outer) each with a recess.
Description & Location
Main Bearing Seals
The bearing seals keep lubricating oil confined to the bearing compartments to reduce oil consumption. They also minimise the leakage of high pressure air from the gaspath into the bearing compartments. Seals are not airtight there is a small flow of high pressure air into the bearing compartments to prevent leakage into the gaspath.
The JT8D has these types of seals installed. Labyrinth, Carbon, split ring and face type, Combination of carbon / labyrinth.
Labyrinth seals on the JT8 can be found at these locations, behind the No1 bearing, in front of the No2 bearing, behind the No3 bearing, in front of the No4 bearing (earlier engins all labyrinth, latter are combination), behind the No5 bearing (combination), in front of the No6 bearing (combination).
Locations, in front of the No4 bearing (face type latter models), behind the No4 1/2 bearing (split ring type), behind the No5 bearing (face type), in front of the No6 bearing (split ring type).
That's about as deep as I will go for now, the other point of note is the tower shaft is supported by a roller bearing at the upper end and a ball at the lower end. Oil is supplied by holes in the bevel gear.