The Pratt & Whitney R-4360 "Wasp Major" was the largest  aircraft piston engine to be mass produced in the United States. Although it found extensive military application, its 28 cylinders, 56 manually-adjustable valves, and 56 spark plugs prevented it from finding favor with the airlines.

R-4360 Firing Order

Cylinder rows are designated A through D from anti-propeller end to propeller end. Cylinder banks are designated 1 through 7, with numbers increasing clockwise, cylinder 1 being the topmost cylinder. Master rods are located in cylinders A7, B4, C4 and D1.


R-4360 Cutaway at the Museum of Flight, Seattle, Washington

Submitted by Robert Wahlgren


QEC on the Boeing maintenance stand, propeller is on right
Carburetor and induction piping
Cylinder and intake manifold with oil drain hose
Left upper engine mount to airframe attach point
Exhaust manifold
Left rear showing generator and cowl flap motor
Engine mount to case
Right side showing generator with cooling hose, starter under it and fire detection sensors



C-97 QEC, R-4360-59B Specifications

Courtesy of Robert S. Wahlgren

Weight 7,988 lb with propeller,
6,500 lb without propeller.
Bore 5.75"
Stroke 6.00"
Displacement 4,360 in³
Compression Ratio 6.7:1
Propeller Shaft Rotation clockwise, 0.375:1 ratio
Spline size 60-A
Maximum dry weight 3,691 lb
Diameter 55.0"
Length 96.5"
Position of CG from rear face of main crankcase 18.4"
CG at crankshaft @ Centerline
Impeller diameter 14"
Impeller Ratio 6.375:1
Carburetor PR100B3-4
Magneto Scintilla S14RN-15
Magneto Ratio 0.875:1
Spark plug gap 0.011" - 0.014"
Spark Advance Normal 20° BTC
Spark Advance Cruise 30° BTC
Cam Timing  
Intake Opens 64° BTC
Intake Closes 76° ABC
Exhaust Opens 135° BBC
Exhaust Closes 79° ATC
Intake Duration 320°
Exhaust Duration 394°
Overlap 143°
Cold valve clearance, not incorporating overhaul change 273  
Intake 0.040"
Exhaust 0.025"
Cold valve clearance with overhaul change 273  
Intake 0.035"
Exhaust 0.035"


R-4360 Cutaway Preparation



Index of Wasp Major and R-4360 Designated Engines (568K Acrobat File)

History of the R-4360 (764K Acrobat File)

R-4360 Service History for C-97 and KC-97 Aircraft in Air National Guard Units



R-4360 Gallery (Warning! Large Files)

Crankcase and Crankshaft
Part Finishing Processes
Cross Section
VDT Schematic
The Variable Discharge Turbocharger (VDT) concept was meant to produce over 4,000 HP and allow piston-powered airliners to fly non-stop from Chicago to London.
VDT 3/4 Rear View
Exhaust ducts, intake ducts, turbochargers and aftercooler dwarf the already large R-4360 engine
R-4360 with Remote Gearbox
This fan-cooled engine with a remotely-mounted propeller reduction gear was used in the Northrop XB-35 "Flying Wing."
Right Side
Right Front
B6 Oil Flow