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Piston Ring size

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Jmccrack	17/03/2015 01:05:10
9 forum posts	I am building a PM 3 steam engine (first one). I have built the piston and cut the grooves. The piston is .501" the bore is .503". The rings are supplied. When I cut the groove and fit the piston ring what should i measure across the OD of the piston ring in the groove.
Jmccrack	17/03/2015 17:30:00
9 forum posts	I have been do some research and I see on a .500" piston the ring should sit below the OD of the piston about .003". Does this sound right?
JasonB	17/03/2015 18:41:56
25215 forum posts 3105 photos 1 articles	No. Are they "O" rings or iron piston rings? if O rings what size section are they they we can give a size. Assuming its a 1/16" nominal "O" ring which actually has a cross section that measures 0.070" then the groove should be 0.090" wide and 0.065" deep measured from the bore so as you have 0.002" gap then the groove should be 0.064" ( 0.065 - 0.001) deep from the piston circumference ( a thou either way won't hurt) The idea is that the groove is not as deep as the rings cross section so it will be slightly squashed when fitted and the over width groove allows it to expand sideways when the pressure is applied eg it goes oval shaped. J Edited By JasonB on 17/03/2015 18:53:20
Jmccrack	17/03/2015 23:05:09
9 forum posts	They are Teflon with a .050" crossection. This is a PM research model 3 steam engine with a brass cylinder and brass piston. Than you for the reply

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