Courtesy of Fred E. Wise, 264 Woodstock Road, Gates Mills, Ohio 44040.
Fred E. Wise
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
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
2plus 1.2 equals
So when this link is adjusted for a 2' displacer stroke the
two cranks are exactly 90 deg. apart. The displacer crank always
leads the power crank in rotation so in this way you can determine
the final rotation of engine.