Lycoming R-680 Aircraft Engine Manuals Collection

This collection brings together 16 historical technical publications covering the Lycoming R-680 series of air-cooled radial aircraft engines, spanning from 1934 to 1948. The R-680 was Lycoming's first aircraft engine — a 9-cylinder, single-row radial that quickly earned a reputation for exceptional reliability and became the primary powerplant for American military training aircraft throughout the 1930s and into World War II. Over 26,000 units were produced between 1930 and 1945, logging millions of flight hours training the pilots who would win the war.

Historical Background

First run in 1929 and type certificated on 4 February 1930 (Type Certificate No. 42), the R-680 was developed by the Lycoming Foundry and Machine Company (later Avco Lycoming), a subsidiary of the Auburn Auto Company. It evolved from the earlier, less successful Lycoming R-645 and was designed to replace the Curtiss OX-5 as the standard American trainer engine.

Military applications included the Boeing/Stearman PT-13 Kaydet, Beech AT-10 Wichita, Cessna AT-8/AT-17 Bobcat, Curtiss-Wright AT-9 Jeep, and Stinson L-1 Vigilant. Civilian applications included the Stinson Reliant, Stinson Airliner, and various Waco S Series aircraft. Post-war, the engine remained popular in surplus trainers and utility aircraft well into the 1950s.

Technical Specifications

• Type: 9-cylinder, single-row, air-cooled piston radial
• Displacement: 680 cu in (11.14 litres)
• Horsepower: 200–300 hp (some models to 320 hp supercharged)
• Bore × Stroke: 4.625 in × 4.5 in (117 mm × 114 mm)
• Compression ratio: 5.3:1 (early) to 7:1 (later models)
• Dry weight: ~505–515 lbs
• Fuel: 73–87 octane
• Carburetion: Stromberg carburettors; Scintilla magnetos
• Construction: Aluminium alloy heads shrunk onto steel barrels with integrated cooling fins

Key Variants

• B Series (e.g., B4E — 225 hp): Early trainer models with front exhaust collectors
• E Series (e.g., E3A — 285 hp): Improved output variants
• R-680-9 (295 hp) / R-680-13 (280 hp): Common high-output military variants
• R-680-10: Supercharged variant producing 320 hp
• R-680-17: Late-war production variant (1944)

Current Status

The R-680 is still flying today, primarily in restored Stearman PT-13 trainers and Stinson Reliants on the vintage and warbird circuit. The current Type Certificate is held by Lycoming Engines (Textron). Active FAA Airworthiness Directives and legacy Service Bulletins apply — operators must track these carefully.

List of Manuals Included

• Manual — Lycoming R-680 Series Aviation Engine — Third Edition — Lycoming Manufacturing Company, Williamsport, Pennsylvania — April 15, 1934
• Handbook of Operation and Flight Instructions — Model R-680-7 Engine and Associated Models (R-680-3, -5, -7 and -11) — T.O. No. 02-15AA-1 — The Aviation Corporation (Lycoming Division) — May 25, 1940 (Revised 5-1-42)
• Handbook of Service Instructions — Model R-680-3 Engine and Associated Models (R-680-3, -5 and -7) — T.O. No. 02-15A-2 — Aviation Manufacturing Corp. (Lycoming Division) — September 20, 1937 (Revised Nov. 10, 1939)
• Overhaul Instructions — R-680-3, -5, -7 and -11 Aircraft Engines — T.O. No. 02-15AA-3 — 20 May 1941 (Revised 15 September 1944)
• Service Instructions — R-680-3, -5, -7 and -11 Aircraft Engines — T.O. No. 02-15AA-2 — 15 January 1941 (Revised 15 September 1944)
• Handbook of Overhaul Instructions — R-680-9 and -13 Aircraft Engines — T.O. No. 02-15AB-3 — April 15, 1941 (Revised 12-20-42)
• Parts Catalog — R-680-9 and -13 Aircraft Engines — T.O. No. 02-15AB-4 — April 25, 1942 (Revised April 5, 1943)
• Service Instructions — R-680-9, -13 Aircraft Engines — T.O. No. 02-15AB-2 — 1 July 1942 (Revised 15 September 1944)
• Operating Instructions — R-680-9 and -13 Aircraft Engines — April 25, 1943 (Revised June 25, 1943)
• Interchangeable Parts List — R-680 Lycoming Aircraft Engines — Class O2-E — T.O. No. 02-15-4 — August 15, 1942 (Revised 1-5-43)
• Table of Limits — Lycoming Aircraft Engines — AN 02-15-1 / A.P. No. 2377A — December 5, 1943
• Operators Manual — Lycoming Type R-680 and R-530 Aviation Engines — Second Edition, Revised June 1939 — Lycoming Division, The Aviation Corporation — Reprinted January 1947
• Overhaul Instructions — R-680-17 Aircraft Engines — AN 02-15AC-3 — 15 August 1944 (Revised 20 June 1945)
• Parts Catalog — R-680-17 Aircraft Engines — AN 02-15AC-4 — February 15, 1944
• Service Instructions — R-680-17 Aircraft Engines — AN 02-15AC-2 — 1 July 1944 (Revised 20 September 1944)
• Overhaul Manual — Lycoming R-680 Aviation Engines — Fifth Edition — Lycoming Division, The Aviation Corporation — 1946 (Reprinted 1948)

Format & Delivery

All documents are provided as high-resolution PDF files, delivered as a compressed archive (RAR/ZIP). To open your download, you will need a free extraction tool such as WinRAR or 7-Zip (Windows) or The Unarchiver (Mac). Once extracted, all files open as standard PDFs on any device.

Export & Compliance Notice

These materials consist of historical U.S. military technical publications spanning 1934 to 1948 (Lycoming series), provided for educational, research, and reference purposes only.

Each document has been reviewed for obvious restrictions and does not display classification markings, export control notices, or distribution limitations on the cover or within the document body.

The publications are sourced from publicly available repositories, including the Defense Technical Information Center (DTIC) and Internet Archive, and are offered in consolidated form for the convenience of researchers, historians, restorers, and aviation enthusiasts.

These materials are not intended for current operational, certification, or repair use, nor for the manufacture or modification of any aircraft or systems.

No ITAR-controlled or EAR-restricted material is knowingly included.

To the best of our knowledge, the materials do not contain currently classified information or content subject to active export restrictions. However, no representation or warranty is made regarding export classification status.

By completing this purchase, you agree to comply with all applicable laws and regulations, including any export or import requirements in your country.