Hot-Air Engine

| July/August 1971

264 Woodstock Road Gates Mills, Ohio 44040

Here are pictures of a Hot-Air-engine recently constructed from an old Briggs & Stratton type FH gasoline engine of about 1920 vintage. Some 'old-timers' will recognize the fact that the cylinder and crankcase have been separated and the cylinder raised enough to give room for the heating-tube. The crankcase now becomes the fire box and the cylinder-head discarded to make room for the new crankshaft and bearing arrangement.

The efficiency of this engine seems higher than any hot-air engine I have seen; I attribute this to the fact that the clearances around displacer and also at the ends of travel of the displacer have been kept to a minimum.

The cylinder has a bore of 2?' and this diameter is carried on down thru the displacer or heating tube. The cast-iron power piston is 2? ' long and has a stroke equal to half the diameter or 1 1/8'. There are no rings but a good sliding fit is important. The sliding fit is important. The displacer is 2 3/16' dia. and 5' lg and made of thin-wall brass tubing. The rod which operates this displacer goes down thru the center of the power-piston and on down thru the top displacer head and then screws into the lower head of the displacer giving more rigidity to its movement. This displacer rod being in the center of the piston makes it necessary to have a piston with a long boss in the center with a long hole accurately centered for the displacer rod. The power-piston connecting rod will be off center which is entirely satisfactory.

The Hot-Air Engine constructed from an old Briggs & Stratton type FH gasoline engine.

Now about the crank throws. In my engine the power throw is 9/16' or half the stroke and is permanently a part of the main shaft. The displacer throw is 1' or half the displacer travel. To obtain a I ' throw it is necessary to have a link of the correct length and be rigidly connected to an extension of the 9/16' power crank-pin. This seems like a tough job but just use a little of your high school trigonometry, like in a right angle triangle the longest side is the sq. root of the sum of the squares of the other two sides -- remember? In my case it was