The text and photos for this article have been reproduced with permission from an ebay advertisment for this engine.


The W.P. Callahan engine known for its trademark of extreme quality and disengaging side-shaft design is one of the rarest and most desirable American built internal combustion engines with only a handful known to exist. The engine has been in the same family for several decades and is now for the first time being offered for sale. The engine which retains its factory appointments down to the ornate main-bearing brass oil port pins is in excellent operating condition exhibiting no sign of appreciable wear. The engine received a cosmetic restoration over 20 years ago which has held up well with the exception of some flaking and soiled paint. The engine has been in storage for the past several years since once having been exhibited on an annual basis at various engine shows. Its late owner was a highly respected collector of engines and related items. He was a proud individual who enjoyed inspiring others and making smiles.

The W.P. Callahan Co. of Dayton, Ohio submitted their first engine patents in 1896. The designer Peter T. Coffield in his patent of March 1897 No. 579,789 detailed a unique crankshaft and spiral gear driven flyball governor that disengaged the side-shaft mechanism when desired operating speed was achieved. Coffield was also associated with the Springfield Gas Engine Co.. William F. Callahan started his career as a cabinet maker and also was involved with the paper making industry. He died in 1903. Callahan advertised a line of engines ranging from 4 hp to 100hp. His engines were known for their innovative design, highly machined and polished surfaces and superb operation. They also had a distinct sound often noted as that of galloping horses due to the design of a disengaging side-shaft that thereby eliminated valve and pump motion when coasting.

This example serial # 2941 as stamped on top of cylinder-head, is believed to be rated as a 10 HP built ca.1899. Details include a 6 ¾” dia. bore x 12” stroke, twin 44 ½” dia. flywheels each with 3” face supported on a heavy cast iron Edwardian Columbian style sweeping front base, 5 ½” dia. hub covers, crankshaft driven, rear-mounted vertical flyball governor with twin 1 ½” dia. balls and ornate brass acorn finial that disengages the rotation of the side-shaft to maintain selected speed, side-shaft driven exhaust and intake valves, all brass side-shaft driven fuel and water pump and carburetor assembly with priming chamber, side-shaft end eccentric with retard and advance lever-cam that drives a spring loaded head–mounted ignitor of the insulated separate electrode and mechanical striker design, original low tension box coil, polished steel head with six finished head nuts, polished steel side-shaft, connecting rod with brass crankshaft bearing, polished steel hubs, governor pedestal and valve-chest. Other fine features include a hinged cast crank-case cover for access to connecting-rod bearing, original main-bearing cap brass belaying pin design oil-port inserts, twin main-bearing Lunkenheimer sight-level oil reservoir gauges each with ornate brass faucet valve, gravity feed cylinder and side-shaft oilers of gravity feed design, original pedestal mounted wiper type connecting-rod oiler, starting lever located at the pedestal mounted governor that manually disengages the side-shaft, wafer type muffler with 2” dia. exhaust piping, front skid-mounted 12” x 20” x 8”, contemporary fuel tank, 12” dia. x 46” copper cooling tank supported on a skid-mounted fabricated steel frame-work, original hand-lever operated brass drain valve with piping, original brass makers plate with last patent date of March 30, 1897, No. and Size not stamped. All mounted on custom oak skids 9) “ in length, overall height to top of flywheel 53”, length over-shaft 38”, overall length of engine from flywheel rim to cylinder-head 70”, overall height to top of water tank 61½”.

The engine has excellent compression with no sign of blow-by. There is no noticeable lost motion in mains, connecting-rod, wrist-pin or side-shaft. With the exception of the fuel and water tank and related piping the engine appears to be very original. There are no noticeable cracks, chips, repairs etc. The flywheels run true. The only damage to the engine (see photo 2nd in from left bottom row) you will notice a water-jacket mounted cast-iron boss. I believe this boss at one time supported a cone-shaped open reservoir receiver that provided visual evidence of circulation of coolant water. Having been by-passed for several decades this cast part could easily be replicated. I have access to one of the other Callahan’s known to exist from which a pattern could be obtained. This deficit does not effect the operation of the engine. I have also been told that this boos could have been a simple cooling pipe support. Any clarification from eBay landmark engine experts would be much appreciated.