The following Panther info is from "Modern Motorcycle Maintenance" by Bernal Osborne of Motor Cycling, Second Edition.

                 PANTHER
        Model: 490cc, 80.
  Makers: Phelon & Moore Ltd., Cleckheaton, Yorks.

Tappet Clearance (hot):
        Inlet, nil.
        Exhaust, nil.

Valve Timing:
        Inlet opens before T.D.C., 25 degrees.
        Inlet closes after B.D.C., 55 degrees.
        Exhaust opens before B.D.C., 70 degrees.
        Exhaust closes after T.D.C., 30 degrees.

Tappet Clearances for Valve Settings (hot):
        Inlet, nil.
        Exhaust, nil.

Ignition Advance:
        38 degrees full advance.

Valve Guides Protrude from Cylinder Head:
        Inlet, .71875 in.
        Exhaust, .71875 in.

Cylinder Bore in Inches:
        3.3145 ins. +001 in.
        Rebore to plus .010 in. when bore exceeds 3.3195 ins.

Piston Clearances:
        Top land, .021 in. to .0225 in.
        Top skirt, .0036 in. to .0041 in.
        Bottom skirt, .0036 in. to .0041 in.

Piston Rings:
        End gap, .010 in.
        Vertical play, .001 in.

Main Bearings:
        Driving side: R. & M. LJ. 1 1/8, (2).
        Timing side: R. & M. LRJ. 1 1/8 A.

Mainshaft:
        End float, .030 in.

Big-end/Connecting-rod:
        Side play, .030 in. to .035 in.

Big-end Bearing:
        Type: Hardened steel, double roller.
        Recondition when noisy.

Fine-limit Diameters:
        Connecting-rod: Little end, .876 in. + .0005 in.
        Camshaft bushes,        ..  .625 in. + .001 in.
        Tappet guides   ..      ..  .3125 in.+ .0005 in.
        Cam-followers   ..      ..  .375 in. + .0005 in.

Note:
        All rocker-box screws are same length with the exception of the centre screw over the push rod tube. If this is inserted in a wrong position there is a danger of cylinder-head breakage when tightening down.

Gearbox:
        Bearings, types and sizes: 52mm by 20mm by 15mm.
                                   72mm by 1 1/2 ins. by 17mm.
        Bushes, (reamed): .9355 in.+.001 in.; .656 in.+.001 in.; .788 in.+.001 in.

Left-hand Threads:
        Large dynamo driving sprocket. (pre 1950 models).

Special Tools Available from Makers for Comprehensive Overhaul:
        Dowty fork key.
        Clutch nut key.
        Engine sprocket remover.
        Crankpin and engine shaft nut spanner.
        Main pinion extractor.
        Ball race fitting tool for frame.
        Tappet stud extractor.
        Exhaust nut spanner.
        Valve removing tool.
        Fork ball fitting tool.

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