Maintenance Inspections
Teledyne Continental Motors, Inc.
TM
7-3.7.2. Differential Pressure Test
Purpose
The Cylinder Differential Pressure Test is a widely used method to determine the internal
condition of cylinders and cylinder components. As with any test or inspection, the
Cylinder Differential Pressure Test has certain limitations that necessitate its use in
conjunction with other non-invasive inspections. TCM requires a “Cylinder Borescope
Inspection” (Section 7-3.7.3) be accomplished in conjunction with the Differential
Pressure Test.
Frequency
Perform the Cylinder Differential Pressure Test:
•
During 100-hour or annual inspections.
•
If excessive oil consumption or blow-by is suspected.
•
If the cylinder exhibits signs of accelerated wear.
In addition to the Cylinder Differential Pressure Test and borescope inspection, further
inspection of any suspect cylinder is recommended according to the guidelines set forth
in this chapter.
It is also important to monitor and record the engine’s oil consumption, the appearance or
color of the engine oil and any visual indications of high crankcase pressure (combustion
blow-by) such as an oily, wet area on the aircraft belly or lower wing surface.
NOTE: Prior to performing the Cylinder Differential Pressure Test,
determine the baseline master orifice calibrated pressure reading
according to Section 7-3.7.2.1 or 7-3.7.2.2.
The purpose of the Cylinder Differential Pressure Test is to identify leaks and the source
of leaks, with the engine under static conditions (not running), using a regulated pressure
source. When performing a Cylinder Differential Pressure Test a regulated test pressure
of eighty pounds per square inch (80 PSI) is directed into the cylinder with the piston at
top dead center at the end of the compression stroke and the beginning of the power
stroke. Eighty pounds per square inch (80 PSI) is used as a test pressure for safety
reasons and is significantly less than the combustion pressure of 800 to 1000 PSI created
during engine operation. Pistons, piston rings, valves and valve seats rely on combustion
forces to assist in creating a complete seal during engine operation.
NOTE: This static leak check does not relate directly to cylinder
pressures developed during actual engine operations.
Excess cylinder wall or piston ring wear, broken piston rings and burned valves will
normally exhibit additional symptoms that must be considered when determining cylinder
condition. These may include, but are not limited to:
•
Excessive cylinder barrel wear and/or piston ring wear:
•
Elevated crankcase pressure; see “Excessive Crankcase Pressure” in Chapter 8.
•
Increased oil consumption. (A sudden increase in oil consumption from the
established or normal trend for the engine or an oil consumption rate that exceeds
1/2 quart (@1/2 liter) per hour during normal engine operation).
•
Oil becoming discolored within first 10 hours after an oil change.
7-12
IOF-240 Series Engine Maintenance Manual
Change 1
31 August 2007
