The A.350 type exhauster, which is fitted to the 4.236 engine, is a rotary sliding vane pump, with an eccentrically mounted rotor.
The exhauster body and end covers are of cast iron, and house an aluminium rotor, die-cast on to a steel shaft. The rotor has four equi-spaced slots to accommodate fibre blades.
The shaft runs in a sintered bronze plain bearing in the rear end cover, and a roller race in the drive end cover, or, alternatively, two sintered bronze bearings. Drive end covers with a roller race have two shaft seals which contact a hardened steel collar pressed on to the rotor shaft. The seals are arranged to prevent ingress of air and dirt, and leakage of oil from the exhauster. Drive end covers with a plain bearing have only one seal, preventing oil leakage.
The shaft drive end is splined to take the drive gear.
The intake port in the exhauster is pipe connected to the vacuum reservoir. The outlet port formed in the end cover of the exhauster aligns with the aperture in the timing case.
Lubrication is by engine pressure feed, oil entering through a connection in the rear end cover to an annular groove in the bearing housing. The oil passes through a hole in the bearing to oilways in the rotor shaft communicating with the slots in the rotor. The oil passes through the end of the rotor slots to lubricate the drive end roller bearing. When a plain bearing is fitted in the drive end cover, it receives oil through an extension of the main oilway in the rotor shaft.
A passage in the drive end cover to the vacuum side of the pump relieves oil pressure on the seal.
At all speeds the rotor blades are kept in contact with the bore of the body by centrifugal force, assisted by the hydraulic action of the oil beneath the blades. When the rotor turns, the spaces between the blades vary because of the eccentric mounting of the rotor in the exhauster body. As a blade passes the inlet port, the space between it and the following blade is increasing and air is drawn from the vacuum reservoir. This air is then compressed and expelled, with the lubricating oil, through the outlet port to the engine timing case.
Periodic Inspections and Preventive Maintenance
Every 5,000 miles (7,500 km) or 250 Hours
Check the vacuum lines and fittings. (Vacuum leakage may occur through the line, or reservoir mounted non-return valve if the valve seat is dirty or pitted). Examine the exhauster for evidence of oil leakage, particularly at end cover joints, and at shaft oil seal.
Check the oil supply line for leaks at fittings and connections.
Check the mounting and end cover nuts and bolts for tightness.
Every 60,000 Miles (90,000 km) or 2,500 Hours
Remove and dismantle exhauster, thoroughly clean all parts and inspect for wear and damage. Repair or replace the exhauster with a Factory Replacement Unit.
Disconnect oil and vacuum pipes at the exhauster and plug ends to prevent the entry of foreign matter.
1. Distance Piece
1. Distance Piece
Undo the four nuts that secure the exhauster to the timing case, and withdraw the unit complete with its driving gear, from the studs (Fig. Q.2).
Remove the two half-round thrust plates which locate the drive gear on the front of exhauster shaft.
Remove drive gear.
Mark the end covers in relation to the body to correct location on re-assembly.
Unscrew four setscrews and remove rear end cover with rubber sealing ring.
Mark the blades in relation to the rotor.
Withdraw the rotor and fibre blades from the body.
Unscrew four socket headed screws, and remove drive end cover, with joint or rubber ring.
Remove rear end cover circlip, blanking disc, and rubber oil seal ring, if fitted.
NOTE: Further dismantling of the rotor assembly need be undertaken only if, after inspection, it is found necessary to renew the bearing or shaft collar.
Cleaning and Inspection Cleaning
Wash the roller bearing, where fitted, in thin flushing oil or white spirit and blow dry with compressed air. Spinning the bearing with compressed air should be avoided, otherwise damage to the rollers and race will occur.
Wash the remaining components in cleaning solvent, and clear the rotor and drive end cover oilways with compressed air.
Inspection of Parts
Examine the roller bearings, where fitted, for discolouration, wear, pitting and cracked races. Rotate slowly to examine for roughness. To renew, see "Overhaul" Section. Premature failure may have been caused by shortage of oil.
Examine plain bearing(s) for excessive wear. To renew, see "Overhaul" Section.
Inspect rotor and shaft for cracks and damage, and the shaft seal collar for wear. To renew collar, see "Overhaul" Section.
Check fit of blades in rotor slots, replace any worn or damaged blades.
Examine the seal(s) carefully to see that the sealing edge is pliable, intact and sharp. Wear or deterioration is caused primarily by dirty oil and grit. Ineffective seals should be replaced. See "Overhaul" Section.
Examine the body for cracks and damage, and the bore for longitudinal ripples or lines. If these are only slight the body is still serviceable, if excessive the body should be renewed.
Examine the end covers, and replace if cracked or scored.
End Cover Bearings and Seals-To Renew
Roller outer race: Tap end cover face several times on to a wooden block, suitably recessed to accommodate the race. Press new race fully into housing.
Seals: Remove circlip, if fitted, and seal outer back plate and remove seals from cover. Fit new seals with inner seal lip facing inwards, and the other outwards. Replace back plate and circlip.
With recessed end cover, remove bearing outer race as above, and withdraw inner back plate. Press outer back plate and seals from cover using a bar or tube 15/16 in (33,34 mm) diameter. Inspect back plates for damage and renew if necessary. Insert outer back plate, press in new seals arranged as above, replace inner back plate, smaller diameter first, and press race into housing.
Where cover has one oil seal, fit new seal with lip facing inwards.
When bearing is housed in a blanked off cover, remove circlip, blanking disc, rubber ring, and press bearing out of cover using a bar or tube 11/16 in (27 mm) diameter. Press new bearing into housing until 1/8 in (3,18 mm) below cover face. Similar action should be taken for a plain bearing in drive end cover.
If the bearing is housed in a blank end cover, it should be extracted, or machined out, taking care not to damage the housing. In an emergency it may be removed by cutting a groove along the bearing, using a narrow half round chisel. Inspect housing and remove any burrs. Press new bush fully into cover.
Roller Bearing and Shaft Collar-To Renew
Withdraw roller bearing inner race and shaft collar using the Churchill Universal Taper Base C.D. 370, and special withdrawal tool C.D. 4221-3 (Fig. Q.4).
Insert the adaptor into the taper base as shown in Fig. Q.3. Position the rotor in the adaptor, drive end up, and insert four "fingers" in the slots with the pegged ends set in the adaptor, and the other ends, against the bearing inner race. Place or screw the appropriate Thrust Block on to the shaft, and while supporting the rotor under the Taper Base, press the bearing and collar off the shaft.
Lightly grease the shaft, and, using the Installer C.D. 44, press bearing inner race on to shaft.
NOTE: There will be a slight clearance between the bearing and the rotor face (Fig. Q.5).
Similarly fit collar with recessed shoulder against the bearing.
NOTE: The rotor assembly should be supported on the bed of the press by a tubular spacer placed over the shaft, and not by the rotor or shaft itself.
Lubricate all moving parts with clean engine oil and renew joint and/or rubber ring(s).
NOTE: No special tools are required to re-assemble exhausters having one oil seal. With exhauster having two seals, use installer C.D. 44.
Where applicable, place the Installer on the shaft to guide the seals on to the collar (Fig. Q.6). Smear the rollers with grease to hold them against the inner race, and insert the end of the rotor assembly into the drive end cover.
Assemble cover to body as originally fitted, with rubber ring or joint, and secure. Dowel pins ensure correct location.
Hold the body, drive end downwards, and replace blades into rotor slots, making sure that marks made during dismantling correspond.
Install rear end cover on to body, with rubber ring, and secure.
Rotate the rotor by hand to be sure that it turns without binding, and tighten the socket headed screws.
Fig. Q.4 illustrates the special Churchill tools for this exhauster.
Refit the drive gear to rotor shaft and secure with two half round thrust washers. Replace the joint and remount the exhauster, aligning the hole in the joint with the air/oil discharge passage, and tighten the four securing nuts.
Reconnect the oil and vacuum pipes.