POWERPLANTS RESOURCE CENTER > GERMANY > PREVIOUS PAGE
Hirth HM 504
The Hirth HM 504 is a four-cylinder air-cooled inverted inline engine. The 504 was a popular engine for light aircraft of the 1930-40s and it was used to power a number of Germany's trainer aircraft of WWII.

Design/Structure:
Type - Four-cylinder inverted inline air-cooled.

Cylinder - Special cast-iron barrels spigotted deeply into crankcase. Light alloy heads, with valve-boxes incorporated, attached by long bolts from crankcase.

Pistons - Nelson-Bohnalie. Three compression and one scrapper rings.

Connecting Rods - Heat-treated chrome-nickel steel H-section rods with roller-bearings in bigg and little ends. Raceways case-hardened.

Crankshaft - Built-up shaft carried on five roller-bearings. Ball thrust bearing.

Crankcase - Elektron coating. Top cover embodies oil tank.

Valve Gear - Fully-enclosed. One inlet and one exhaust valve per cylinder. Inlet valve seat of special bronze. Exhaust valve seat of special steel. Valve-rockers, on needle bearings, operated through push rods and ball ended tappets off camshaft running in roller-bearings.

Carburation - One Pallas-Zenith 40 VAH carburetter suitable for inverted flying and fitted with automatic mixture control.

Ignition - Two Bosch JFR.ABS.48 and 49 magnetos, one with impulse starter. System fully screened.

Lubrication - Crankcase cover serves as oil tank. Metered oil feeds to airscrew thrust-bearing and cylinders. Big-end and main bearings oil-splashed.

Starter - Hand-turning crank with back fire safety device.

Airscrew Drive - Right-hand tractor, direct-drive, Hirth hub.

Specifications: HM504A-2
Displacement:
  Capacity: 3.984 Litres (243 cu. in.)
  Bore: 105mm (4.128 in.)
  Stroke: 115mm (4.52in.)
  Compression ratio: 6.2:1
Dimensions:
  Length: 960mm (33.75 in)
  Height: 780mm (30.70 in)
  Width: 520mm (20.4 in)

Weights:
  Dry and Bare: 112 kg (245 lbs.)
  Fully equipped: 124 kg (274 lbs.)

   Performance:
  Maximum: 105 hp @ 2,530 rpm.
  Rated: 85 hp @ 2,360 rpm.
  Cruising: 75 hp @ 2,270 rpm
  Cruising Consumption:
    Fuel: 220 grams (.485 lb) per horsepower hour.
    Oil: 3 grams (.0066 lb) per horsepower hour.
  Power-to-weight ratio: 2.87 lb/hp at cruise speed
Applications:
– Bücker Bü 131
– Bücker Bü 181
– Klemm Kl 35

Sources:
Jane's All The Worlds Aircraft 1943-1944, New York, The Macmillan Company

POWERPLANTS RESOURCE CENTER > GERMANY > PREVIOUS PAGE