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      The following instructions are for machine shops, white metalers and others who have purchased rough castings only                                                                     

 

Suggested order of work

for finishing rough cast white metal main bearings

 

 

 

1        Prepare bearings for machining (see bottom of page)

2        Drill any oil holes

3        Make a dummy housing to hold shells stable and circular

4        Rough machine (ie: in lathe) leaving approx 0.050˛. Large cuts of approx 0.100˛ may be taken at this stage.

5        Machine oil grooves

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   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

 

Notes on preparing 

white metal bearings castings for machining

 

Bearing shells

 

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

 

1)        Remove paint from the shell back with a suitable solvent or wie brush – any traces of white metal on the shell back may be lightly filed until smooth.

2)        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 4.

3)        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.

 

 

4)        The flash (overspill white metal) can be removed from the edges of the shell by milling until a thin layer is left. Finish by carefully filing until the shell tops are just visible – and no more. NB: It is vital not to over file the edges or bearing “nip” will be lost causing a loose fit in the housing. If a mill is not available the flash may be removed completely by filing.

 

Direct cast con rods and caps etc.

These do not normally close in after casting, therefore steps 1 to 3 can be omitted

 

 

 

             To contact us: Phone 01725 511684    

                                    Fax 01725 511684     

Email: Enquiries@formhalls.com 
Formhalls Vintage & Racing Ltd. Greycott, Lower Densome Wood, Woodgreen, 
New Forest, Hampshire, SP6 2BE England

(Callers by appointment only please)

   Practicing Preserving and Passing on British Tradition