After casting, bearing shells will usually pull in at their edges and will require opening out and re-fitting to their housings before machining.
Procedure A) Remove paint from the shell back with a suitable solvent or wire brush – any traces of white metal on the shell back may be lightly filed until smooth.
B) Try the cast shell in its housing – the shell should be a light “spring” fit. If the edges of the shell are gripped by the housing proceed to step D.
C) With the cast shell on its back on a solid flat surface, lightly pein (gentle taps only) the cast surface with a half-pound ball pein hammer (as diagram). Start peening in the centre of the bearing, in rows, gradually moving out each side towards the edges. Repeat until shells fit (as section B)
D) The flash (overspill white metal) can be removed from the edges of the shell by milling or filing until a thin layer is left. Finish by carefully rubbing with 250 grit wet & dry (avoid abrasive contacting bearing surface or particles may inbed in the surface causing rapid wear) until a nip of approx 0.002" to 0.008" is obtained . NB: It is vital not to over file the edges or bearing “nip” will be lost causing a loose fit in the housing.
NB: New shell backs are supplied with extra nip which must be carefully removed until the desired nip is achieved (typically 0.002² to 0.006²) – failure to do this may damage the bearings and housings
2 Drill any oil holes – New shell backs are normally supplied without holes drilled to aid white metal casting
3 Make a dummy housing to hold shells stable and circular
4 Rough machine (ie: in lathe) leaving approx 0.050². Large cuts of approx 0.100" to 0.200" may be taken at this stage.
5 Machine oil grooves & gutterways (mudgullies)
6 Bolt crank cases to block (if separate)
7 Set up on line boring equipment, aligning on front and rear bearing housings
8 Fit shells to respective housings ensuring that they are clearly marked for future reassembly to their machined positions
9 Torque nuts and / or bolts to final (assembled) figure
10 Line bore with final cut of approx 0.002" to 0.005". A clearance of 0.002" / 0.0025" is common for journal diameters of around 2"
11 Machine thrust faces to set crank shaft end float
12 Machine surplus white metal from edges of remaining bearings as necessary
13 Chamfer / radius all edges to clear journal radius
14 Dismantle equipment and bearings (ensuring that all relocation marks are still visible) and de-burr as necessary
After casting, bearing shells will usually pull in at their edges and will require opening out and re-fitting to their housings before machining.
