Just completed my second hot air engine (the first wouldn't run :( ) and here are a couple of pics.
It's to my own design, a shameless cobbling-together of various other engines I've seen on the net and I've almost finished drawing up the plans. It's water-cooled has a 9mm dia power piston and 12mm stroke. The displacer is 34mm long (12.5mm dia) and the displacer chamber is 50mm (about 13.5 internal dia).
The materials are mild steel, brass and some DIY-store cold rolled tube for the displacer chamber and water holder (actually the cylinder body is bronze but looked like brass before I started working it!). The permanent joints are all silver-soldered.
I've spent ages tweaking this and that, lapping the cylinder etc to reduce friction but it just wouldn't go - until I showed it the warm end of a blow-torch rather than a puny meths-powered burner :) Trouble is it will only run for a very few seconds, partly because the water gets very hot and because I'm worried about melting the solder on the end-cap!
......A nice standard 90 deg cyl. configured Gamma thats showing signs of life. Standard troubleshooting proceedures apply. Air Leaks: with heat applied to attemp a run, pour a half cap full of rubbing alcohol right on top of the power piston and spin it over......any change? The alcohol will fill in the gap between the piston and cyl. for a better seal and evaporate without a trace shortly. If you have an air compressor, remove displacer cyl and with blowoff nozzle with rubber tip and air compresser set to low PSI, blow thru the air transfer hole back to the power cyl. Piston will go to the top of its bore and leaks will sound off around the piston. Check displacer cyl. seal by reversing air nozzle check. Pull out power piston and with nozzle sealed against the power cyl. and blow back to the hot cap. You will hear a leak at the gland bushing/ displacer pushrod which is O.K. Is the seal between the hot cylinder to its mounting block holding? Friction: WD40 a couple of drops to the pushrod thru the gland. This spot without a little lub will stop a running engine. Disconnect the conrod to displacer push rod and rotate/ push in and out and listen for displacer rubbing inside of hot cap bore. OK all done? Now what your real problem is...........you have too steep of a rod angle for the power piston! Your con rod is too short! You are going to have to raise the flywheel axle and use a longer con rod. This will give less angle to the rod at the 9 and 3 O'clock crank position and drive the piston strait down the bore instead of pushing it into the side of the cylinder.. Longboy.
