Thanks for the instruction Terry I think I shall be okay with it now.
Rich, Unfortunately I'm afraid I can't part with the piston / liner that I have but you may be able to pick up an old 'externally abused' example of a Rapier somewhere – good examples of the early green head versions can certainly fetch a few bob but the later ones are not quite so sought after.
The dimensions (mm) of this set up are as follows….
Overall length of liner – 32.1
Distance from bottom of liner to exhaust flange – 10.5
Thickness of exhaust flange – 3.75
Diameter of exhaust flange – 21.7
Diameter above exhaust flange – 17.99 (good slide fit into cylinder head)
Diameter below exhaust flange – 18.1 (Not critical, the annular gap acts as one big transfer passage)
Width of exhaust and transfer ports is 1.58 (1/16) (The top of the transfer port is level with the bottom of the exhaust flange. The exhaust port lower edge is set .8 above top of transfer port )
Bore is 14.67
Piston wall height – 10.8. Piston has a conical top – overall height is 13.25
Pin offset from top of wall is 6.5
Con-Rod length is 24.4
This liner is hardened but were I to make one for myself I would use ordinary EN1a which is a good combination with a cast iron piston. If you already have a piston in reasonable condition it would probably be worth re-lappping this first then make the liner a thou or so down on the piston size to allow for lapping the liner.
One other point – the four exhaust and transfer ports are cut such that the pillar left between them is very small ( I believe some engines were made with three ports) Personally I would cut these less deep to give a wider pillar say 3-4mm wide. This will have very little if no effect on performance but will make for a stronger liner.
Reclaiming small engines like this has always given me a great deal of satisfaction so good luck with yours
Regards – Ramon