1937 65 HP Cooper-Bessemer Type GSD

Engine becomes an homage to a departed brother

| October/November 2004

  • 1937 Cooper-Bessemer Type GSD
    Dean Unruh's 1937 Cooper-Bessemer Type GSD got a warm reception at the 2004 Oklahoma Steam & Gas Engine Show.
  • Pistons
    Pistons
  • Cylinder
    Cylinders
  • The flywheel
    The flywheel after removal and sandblasting.
  • The 'merry-go-round' oiler
    The 'merry-go-round' oiler that originally oiled both cylinders.
  • The engine starts to go back

  • Cooper-Bessemer Type GSD
    The restoration almost complete. At this point the pony motor had been installed, but the air compressor and air tank had yet to be mounted.
  • Dean Unruh and Stan Melrose
    Right: A younger-looking Dean Unruh and neighbor Stan Melrose lowering the cylinder onto the engine block in 1989. The guys still had a long way to go, but it was coming together one piece at a time. Notice the custom trailer with its cross-mounted suppor
  • Cooper-Bessemer

  • Oak brake shoe
    The oak brake shoe
  • The air holding tank
    The air holding tank
  • The engine's placard
    The engine's placard
  • The screen cooler.
    The screen cooler.
  • 1937 Cooper-Bessemer Type GSD

  • The engine block
    The engine block
  • Crankshaft
    Crankshaft

  • 1937 Cooper-Bessemer Type GSD
  • Pistons
  • Cylinder
  • The flywheel
  • The 'merry-go-round' oiler
  • The engine starts to go back
  • Cooper-Bessemer Type GSD
  • Dean Unruh and Stan Melrose
  • Cooper-Bessemer
  • Oak brake shoe
  • The air holding tank
  • The engine's placard
  • The screen cooler.
  • 1937 Cooper-Bessemer Type GSD
  • The engine block
  • Crankshaft

Company: Cooper-Bessemer; manufactured in Mt. Vernon, Ohio, and Grove City, Pa.
HP: 65 at 600 RPM
Serial number: 39852
Bore: 7-1/2-inch
Stroke: 9-inch
Additional info: Originally pumped a 6,100-foot-deep oil well in Coal County, east Oklahoma; Two-cycle engine, 5.3-to-1 compression ratio; decommissioned in 1975; 4,500 pounds total, 910-pound flywheel; burns propane or natural gas

The green beast quietly lays in wait. Quickly, Dean Unruh jumps on the 18-foot trailer. He positions himself near the 4,500-pound 1937 65 HP Cooper-Bessemer's broad base and reaches toward the apex of the engine to open an air valve to the cylinder head. With a glance at a check valve and a notice of a petcock, everything looks ready to go as he gives a nod to his buddy below.

Perry Hildebrandt turns a valve extending from an air tank to introduce 160 psi of air into the engine's cylinder head, while Dean nimbly jumps down to the ground to roll the engine's big 910-pound flywheel over Top Dead Center. A cam off the crankshaft in time with the pistons introduces the pressurized air needed to start the lumbering two-cycle engine. Throngs of people have gathered to witness the rare upright 65 HP oil field engine run at the 2004 Oklahoma Steam & Gas Engine Show in Pawnee.

'The engine will easily flood if you don't watch what you're doing,' Dean says over the din coming from the Cooper-Bessemer. 'The carburetor just can't adjust.' The crowd looks on in amusement, cluelessly taking the difficult start-up for granted. Dean walks around the engine, inspecting all things large and small on the engine and trailer for problems. It takes an eagle eye, and it's a duty that only comes with years of experience starting the engine.



Dean knows the subtle intricacies on his Cooper-Bessemer Type GSD, serial no. 39852, because he's been exhibiting it at Pawnee and other nearby shows for almost 15 years. It's his largest and favorite engine in his collection, but sadly the Cooper-Bessemer holds deep sentimental ties since his brother Marlin, who helped him restore and show the engine, passed away three years ago.

'That was our favorite engine ... we had so many memories and hours on that engine,' the Enid, Okla., native affectionately recalls about his time spent with Marlin restoring the engine. 'We were partners on this stuff - when I see that engine, I see Marlin. It was our favorite because it's come such a long way. We thought it was hopeless.'