Piston to Cylindar Sealing

[MechEng]

Hello everyone, I Just found your website and it seems to be exactly what I was looking for.

I am thinking about making a stirling engine and have a few questions. If the cylindar is made of aluminum what metal do you guys recommend for the piston? I heard that aluminum on aluminum causes galling. Also do you guys use piston rings? If not what do you do to seal the piston and bore? Lasty, what type of clearance do you typically see between the piston and cylindar to limit friction but still allow good sealing and no piston twisting?

 

[Stan]

I have made several stirling engines. All have aluminum cylinders and some have brass piston and some graphite piston. No piston rings and powdered graphite used for lubrication and seal on brass piston, nothing on graphite piston. My piston fit is determined by trial and error. After boring the cylinder to the best surface finish I can get, I make a piston to just slide easily in the bore.

 

[idahoan]

Hello

I agree with Stan; I would guess the fit to be around .0005" of piston Clarence. The bore needs to be round, straight and preferably a lapped or honed finish. The piston should be able to fall freely through the bore and if the end of the cylinder is plugged (say with your hand) the piston should stay where ever it is, and not fall out. An air tight seal and no friction is paramount.

Dave