Allison Engine Circular Letters

Circular Letters, Service Bulletins, Information Letters - specific technical information has been known by many names over the years. The 112 Allison Engine circular letters below that were added to AirCorps Library this week are all dated between 1944 and 1945. It's crazy to think how many more they would have published in total after looking at this incredible amount of information! This collection came to us from the Allison guru Dan Whitney - many thanks!

Click the links on each to view preview images of each manual, and purchase a download if you'd like. Or, if you'd like to just read them all first, become a member of the AirCorps Library site and get started!

C-15 Accessory Housing Vent Connections, Circular Letter No. 164, 9-May-1944

Chafed or Frayed Ignition Switch Wires Conducive to Backfiring, Circular Letter No. 165, 9-May-1944

Reported Effect of Uninhibited Ethylene Glycol on Coolant Pump Seals, Circular Letter No. 166, 17-March-1945

Installation of NaMBT Inhibited AN-E-2, Ethylene Glycol in Installations Previously Operated with AN-E-2 GlycolPart #42206 BH Scroll, Auxiliary Supercharger, Circular Letter No. 167, 16-May-1944

Carburetor Idle Spring, Circular Letter No. 168, 17-July-1944

Manifold Pressure Gauge Line P-38J, Circular Letter No. 169, 18-May-1944

Spring - Oil Pressure Relief Valve - Part #54464, Circular Letter No. 170, Circular Letter No. 170

Modification of PT-13E9 Carburetor Setting of Dry Installation, Circular Letter No. 171A Supplement, 28-June-1944

PT-13E9 Carburetors - Matching with Discharge Nozzles, Circular Letter No. 171A, 28-June-1944

Nozzle - Reduction Gear Pinion Oiler - Part No. 40962, Circular Letter No. 172, 19-May-1944

Outboard Reduction Gear Rear Case Change to Accommodate Larger Mounting Studs, Circular Letter No. 173, 19-May-1944

Spray Nozzle Gaskets, Circular Letter No. 174, 19-May-1944

Carburetor Throttle Rod Binding Caused by use of Large Washer, Circular Letter No. 175, 29-May-1944

Information on the V-3420-23 (-B10) Model Engine, Circular Letter No. 176, 2-June-1944

Coolant System Pressure Relief Valve Information, Circular Letter No. 177, 6-June-1944

Coolant System Pressure Relief Valve Information, Circular Letter No. 177 Supplement, 25-July-1944

Cross Over Baffle -93 Engine, Circular Letter No. 179 Supplement, 6-July-1944

Cross Over Baffle -93 Engine, Circular Letter No. 179, 28-June-1944

Fires in P-38 Aircraft, Circular Letter No. 180, 6-July-1944

Jet - Supercharger Vent Air Metering - Part #53998, Circular Letter No. 181, 8-July-1944

Operation and Maintenance on V-3420-23, B-10, Circular Letter No. 183A, 19-Aug-1944

Handling of Engine Parts in Process of Overhaul, Circular Letter No. 184, 25-July-1944

Briggs Clarifier Operation, Circular Letter No. 185, 26-July-1944

Water Injection Pump Switch, Circular Letter No. 186, 2-Aug-1944

Jacobson Test Stands, Circular Letter No. 187, 2-Aug-1944

Carburetor Air Screens, Circular Letter No. 188, 25-Aug-1944

Compression Check Method, Circular Letter No. 189, 25-Aug-1944

Carburetor Air Temperature and Mean Effective Pressure Charts, Circular Letter No. 190, 30-Aug-1944

Supercharger Drive Gear Train 9.6 to 1 Ratio, Circular Letter No. 191, 14-Sept-1944

P-63 Installation Fire Hazard, Circular Letter No. 192, 5-Sept-1944

Torque - External Nuts and Screws, Circular Letter No. 193 Supplement, 30-Mar-1944

Torque - External Nuts and Screws, Circular Letter No. 193

Air Passage Hole in Supercharger Inlet Cover, Circular Letter No. 194, 12-Sept-1944

Aerated Accelerating Pump and Water in Fuel System on P-63 Aircraft, Circular Letter No. 195, 13-Sept-1944

Low Oil Pressure in Overhauled Engines on Test Stands, Circular Letter No. 196, 14-Sept-1944

Auxiliary Stage Supercharger Mounting Bosses, Circular Letter No. 197, 19-Sept-1944

Magneto Timing Control D.F.L.N.-5, Circular Letter No. 198 Supplement, 13-Nov-1944

Magneto Timing Control D.F.L.N.-5, Circular Letter No. 198, 21-Sept-1944

Cotter Pins Engine Proper Reduction Gear and Aux. Stage, Circular Letter No. 199, 27-Sept-1944

Pipe Plugs Engine External, Circular Letter No. 201, 27-Sept-1944

Distributor Heads and Fingers, Melmac, Moisture Absorption, Circular Letter No. 202, 27-Sept-1944

Coolant Leaks, Circular Letter No. 203, 28-Sept-1944

P-63 Auxiliary Stage Oil Starvation, Circular Letter No. 204, 29-Sept-1944

Distributor Needs Low Voltage Continuity Check of Cable Connections, Circular Letter No. 205, 17-Oct-1944

Carburetor Settings - 91 Versus 100 Octane Fuel, Circular Letter No. 206, 12-Oct-1944

Carburetor Settings - 91 Versus 100 Octane Fuel, Circular Letter No. 206, 22-Dec-1944

Distributor Heads and Fingers - Cleaning, Circular Letter No. 207, 17-Oct-1944

Water Injection - Why We Use It, Circular Letter No. 208, 18-Oct-1944

Oil Temperature Operating Limits, Circular Letter No. 209, 20-Oct-1944

Oil Temperature Operating Limits, Circular Letter No. 209A, 23-Oct-1944

Oil Baffle Screws, E Reduction Gear Assemblies, Circular Letter No. 210, 20-Oct-1944

Tool Kits - Engines, Circular Letter No. 211, 20-Oct-1944

Propeller Shaft Thrust Bearing Oil Seal - Replacement on F Engines, Circular Letter No. 212, 26-Oct-1944

Dow-Corning Compound #4 Stock No. 7300-223100 as Recommended in T.O. 03-5E-1, Circular Letter No. 213, 26-Oct-1944

Piercing Screws - Distributor Heads, Circular Letter No. 214, 30-Oct-1944

Cylinder Stud to Block Oil Seal #54143, Circular Letter No. 215, 30-Oct-1944

Vapor Vent Needle - Carburetor, Circular Letter No. 216, 8-Nov-1944

Vapor Vent Needle - Carburetor (Float Modification), Circular Letter No. 216, 24-Jan-1945

Carburetor Mixture Setting - P-40N-40, Circular Letter No. 217, 13-Nov-1944

Engines Cutting Out on Take-off P-40, Circular Letter No. 218, 13-Nov-1944

Coupling Assembly -Magneto Timing, Circular Letter No. 219, 13-Nov-1944

Water Line - Plug - Dry Operation, Circular Letter No. 220, 13-Nov-1944

Screw, Throttle Valve, Part #P15737 - Carburetor, Circular Letter No. 221, 28-Nov-1944 Hydrometer Type Coolant Testers for Determination of Ethylene Glycol Concentration, Circular Letter No. 222, 4-Dec-1944

Plug Assembly - Supercharger Drain, Circular Letter No. 223, 13-Dec-1944

Distributor Finger, Melmac, #10-28705, Cracking at Mounting Flange, Circular Letter No. 224 Supplement, 6-Mar-1945

Distributor Finger, Melmac, #10-28705, Cracking at Mounting Flange, Circular Letter No. 224, 28-Dec-1944

Carburetor Jet Change, K-8, on -111 & -113 Engines, Circular Letter No. 225, 28-Dec-1944

Screen - 54391 Aux, Stage Supercharger Vent -93 & -117 Engines, Circular Letter No. 226, 15-Jan-1945

Low Oil Temp P-40N-40, Circular Letter No. 227 Supplement, 18-Jan-1945

Low Oil Temp P-40N-40, Circular Letter No. 227, 15-Jan-1945

Coolant Line Chafing P-63, Circular Letter No. 228, 17-Jan-1945

Spark Plug RP-43, Circular Letter No. 228, 22-Feb-1945

Rubber Covers Placed on Auto Mixture Control Units - Carburetor, Circular Letter No. 229, 17-Jan-1945

Spark Plugs RP-43, Circular Letter No. 231 Supplement, 22-Feb-1945

Spark Plug RP43S Released for Use in Production Engines, Circular Letter No. 231, 17-Jan-1945

Generator Protection - Voltage Regulator Maintenance, Circular Letter No. 231, 22-Jan-1945

Limiting Power of V-1710 Engines in Domestic Operations, Circular Letter No. 234, 30-Jan-1945

Coolant System Filling Procedure for P-39 & P-63 Ships, Circular Letter No. 235A, 26-Feb-1945

Loss of Manifold Pressure and Auxiliary Stage Oil Pressure While Performing Acrobatics P-63, Circular Letter No. 236, 1-Feb-1945

Retorquing Rocker Arm Stud Nuts, Circular Letter No. 263A, 24-Sept-1945

Preparation of Engine for Service After Extended Storage, Circular Letter No. 237, 1-Feb-1945

Pressure Gage - Fuel and Oil, Circular Letter No. 238, 26-Feb-1945

Oil Tank Access Door P-38, P-40 & P-51, Circular Letter No. 239, 14-Feb-1945

Coolant Expansion Tank Support Bracket P-63, Circular Letter No. 240, 22-Feb-1945

Carburetor Mixture Control Plate #70 Bleed Hole -111, -113, -115 Engines, Circular Letter No. 241, 1-Mar-1945

Oil System Servicing P-63, Circular Letter No. 242, 6-Mar-1945

Airscoop - P-63 Target Ships, Circular Letter No. 243, 7-Mar-1945

Valve Spring Fatigue, Circular Letter No. 244, 8-Mar-1945

Oil Tank Support Assemblies - P-63 Replacement of Burtex Pads, Circular Letter No. 245, 12-Mar-1945

Reduction Gear Case, Outboard - Change & Identification of Oil Baffle Plate, Circular Letter No. 246, 13-Mar-1945 Oil Hopper Tank Sump Drain, Circular Letter No. 247, 20-Mar-1945

Nut - Propeller Shaft Thrust Bearing Retainer #41058, Circular Letter No. 248, 22-Mar-1945

Check Valve - Oil Separator to Oil Return Line - P-63, Circular Letter No. 249, 28-Mar-1945

Nut - Oil Filter Sleeve, Part #44655, Circular Letter No. 251, 3-April-1945

Alcohol - Water Pressure - Spasmodic Flow, Circular Letter No. 252, 10-April-1945

Cover - Supercharger Inlet, Part #54026, Circular Letter No. 253, 5-May-1945

Tube - Regulator Oil Pressure, Part #44297, Circular Letter No. 254, 9-May-1945

Fuel Consumption Installation - Apparent Differential in P-38 Installation, Circular Letter No. 255, 15-May-1945

Chafing - RP-63 Target Ships, Circular Letter No. 256, 19-May-1945

Plug - 3- inch Square Shank Pipe, Part #54833, Stainless Steel, Circular Letter No. 257, 29-May-1945

Stud #43127 - Intake Manifold Lower Boss, Circular Letter No. 258, 31-May-1945

Carburetor Major Setting Variables, Circular Letter No. 259, 31-May-1945

Water Injection Operation Following Engine Change, Circular Letter No. 260, 14-June-1945

Induction Pipe Stud, Method of Locking, Circular Letter No. 261, 27-June-1945

Part Number Changes to be Accomplished at Overhaul when Complying with T.O. 02-5AD-12, Circular Letter No. 262, 29-June-1945

Retorquing Rocker Arm Stud Nuts, Circular Letter No. 263A, 24-Sept-1945