This was the engine that powered Chet’s Waco ZQC-6 aircraft. For clearances between parts, the number given is in thousandths of an inch. A negative number means a tight clearance. Where three values are given, the first and second numbers are the maximum and minimum clearance for a new part, and the third number is the maximum clearance due to wear before replacement is required.

Inlet valve stem to valve guide clearance2, 3.5, 8
Exhaust valve stem to valve guide clearance3, 4.5, 10
Inlet valve guide to cylinder-0.5, -1.5, N/A
Valve cam follower to follower guide0.3, 0.7, 3.5
Desired exhaust valve tappet clearance, cold.8
Desired inlet valve tappet clearance, cold.8
Piston to cylinder clearance at top land.49.5, 53.5, N/A
Piston to cylinder clearance at skirt.25, 27, 32
Piston ring gap in cylinder.N/A, 37.5, N/A
Side clearance of top piston ring in piston groove.4.5, 6, N/A
Side clearance of second piston ring in piston groove.3.5, 5, N/A
Side clearance of third piston ring in piston groove.3.5, 5, N/A
Slide clearance of bottom piston ring in piston groove.3.5, 5, N/A
Piston pin in piston pin hole.-0.5, 0.2, 3
Piston pin in connecting rod.1.5, 2.2, 5
Master or connecting rod bearing on crank pin.2, 4, 6.5
Knuckle pin in link connecting rod.0.3, 1, 3
Knuckle pin in master connecting rod.-0.4, -1, 0.1
Nominal cylinder bore diameter.5 1/2
Permissible “out of round” before cylinder rebore is required.3
Permissible cylinder taper before rebore is required.5
Permitted number of rebores of 0.010″ each.1
Magneto point clearance desired.12
Spark-plug clearance desired, porcelain.N/A
Spark-plug clearance desired, mica.15
Spark advance, degrees before top dead centre30
Inlet valve opening, degrees before top dead centre18
Inlet valve closes, degrees after bottom dead centre65
Exhaust valve opening, degrees before top dead centre58
Exhaust valve closing, degrees after top dead centre16
Oil pressure at normal speed, minimum (upper number) and maximum (lower)60, 90
Minimum operating oil temperature, degrees F.100
Maximum operating oil temperature, degrees F.170
Maximum permissible cylinder head temperature, degrees F.550
Recommended SAE oil viscosity number, summer (upper number) and winter (lower number)120, 60
Recommended minimum fuel octane number75
Maintenance specifications for Jacobs L-5 aircraft engine, from Lusk, H.F. (1940) General Aeronautics. New York: Ronald Press Company