Hirth HM 504 — Engine Manuals Collection
A curated archival collection of primary-source technical documents covering the Hirth HM 504 — the highly successful 4-cylinder inverted inline engine that became the standard powerplant for European light and trainer aircraft through the 1930s and 1940s, powering the iconic Bücker Bü 131 Jungmann and Arado Ar 79 and training thousands of pilots across two continents.
Collection Overview
Total Unique Manuals: 8
Variants covered: A
Variant A — 7 Manuals
HM 504 A Operating and Maintenance
- HM 504 A Aircraft Engine Operating and Maintenance Manual 1936, Betriebs- und Wartungsvorschrift (German Language)
HM 504 A Installation and Assembly Instructions
- HM 504 A-2 Aircraft Engine Installation and Technical Data Documentation, Einbauunterlagen (German Language)
HM 504 A Repair Instructions
- HM 504 A-2 Aircraft Engine Operating, Maintenance and Partial Overhaul Manual, Betriebs-, Wartungs- und Teilüberholungsvorschrift (German Language)
HM 504 A Illustrated Parts Catalog
- HM 504 A-2 Aircraft Engine Operating Instruction and Illustrated Parts Catalog, Betriebsanweisung und Ersatzteilliste (German Language)
HM 504 A Technical Publications
- HM 504 A-2 Aircraft Engine Technical Textbook Volume 23, Luftfahrt-Lehrbücherei Band 23 (German Language)
- HM 504 Aircraft Engine Description from Arado Company Publication, Werksschrift (German Language)
HM 504 A Technical Reports & Certificates
- HM 504 A Aircraft Engine Data Card, Motoren-Karte (German Language)
No-Variant Manual — 1 Document
HM 504 Engine Subsystems
- SUM-Vergaser 762 Carburetor Description and Illustrated Parts Catalog, SUM-Vergaser 762 für HM 504 (German Language)
About the Hirth HM 504
Historical Background
First introduced around 1934 as part of the Hirth Motoren “500” engine family, the HM 504 was produced through approximately 1945 with an estimated 6,000 units built. It powered primary trainers including the Bücker Bü 131 Jungmann and Bücker Bü 181 Bestmann for the Luftwaffe, and civilian types including the Arado Ar 79 and Klemm Kl 35. The engine was licensed to Japan as the Hitachi Hatsukaze Model 11, seeing wartime and post-war use in training and liaison aircraft.
Technical Specifications
- Type: Inverted inline, 4-stroke air-cooled piston engine
- Configuration: 4-cylinder inline (inverted)
- Displacement: 3.98 L (243 cu in)
- Bore × Stroke: 105 mm × 115 mm (4.128 in × 4.52 in)
- Power Output: 88.7–105 hp at 2,400–2,530 RPM
- Compression Ratio: 6.2:1
- Weight: 123.8 kg (273 lbs)
- Fuel: 77–80 octane aviation gasoline
Engineering Distinction
The HM 504 features a cast magnesium alloy (Elektron) crankcase for exceptional weight reduction and the patented Hirth built-up crankshaft supported throughout by roller bearings — delivering outstanding power-to-weight ratio and low oil consumption for its era.
Current Status
The HM 504 remains airworthy in restored vintage aircraft including the Bücker Bü 131 Jungmann and Bü 181 Bestmann, maintained under legacy Airworthiness Directives for vintage/historical restoration. Various independent overhaul shops and heritage organizations hold approvals to maintain airworthy engines in restored historical airframes.
This is an archival, static-copy edition fixed at its original publication date. Intended for historical reference, flight simulation, museum restoration, and educational use only. Not approved for active airworthiness maintenance under FAA 14 CFR § 43.13, EASA Part-M, or equivalent international regulations. Operators of active aircraft must use current, revision-controlled publications from the Type Certificate holder or an authorized distributor.
⚠️ Regulatory Notice: Under FAA 14 CFR § 43.13 and EASA Part-M, any mechanic performing maintenance on an active aircraft must use current, manufacturer-approved revision-controlled data. This archival document does not satisfy that requirement.
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