Calculating piston length

[Former MemberParticipant @formermember19781]

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[Former MemberParticipant @formermember19781]

calculating piston length.

[HopperParticipant @hopper]

No idea what the original Puffin drawings specify, but from your measurements, I'd be thinking along the lines of 19mm cylinder minus 11mm of stroke leaves a space of 8mm. Leave 1mm clearance at each end, so deduct 2mm total to leave 6mm.

That's your maximum piston length. Now to accommodate the steam ports you can file or machine a small notch from each steam port up to the cylinder head gasket surface. This can be done by dropping a small slot drill down the side of the bore, or with a Dremel tool or similar. It will let the steam up past the piston side to the head space.

That would be my thinking to get it running anyway. Puffin's designers may have done it differently.

[Former MemberParticipant @formermember19781]

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[Paul KempParticipant @paulkemp46892]

Don't forget to allow for any spigot protruding into the bore from the cylinder covers. As above will be fine for flat covers but if spigoted the piston will clout em if deeper than the 1mm allowed clearance.

Paul.

[Former MemberParticipant @formermember19781]

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[Brian Sweeting 2Participant @briansweeting2]

Perhaps machine a Delrin piston first to see how it fits before the final metal version.

[JasonBModerator @jasonb]

Looking at a couple of exploaded views on the net, I would say 5-6mm looks in proportion to the bore.

[Former MemberParticipant @formermember19781]

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