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Compression measurement in cylinders

This appendix establishes the procedure for measuring compression in the cylinders of an internal combustion engine. It applies both to preparing the engine for measurement and to performing the measurement itself with a compression gauge.

Procedure for measuring compression in the cylinders of an internal combustion engine.

Procedure

1. Warm up the engine to operating temperature.
2. For petrol engines, disconnect the leads from the spark plugs, switch off the Hall sensor and the fuel supply to the cylinders, and unscrew all the spark plugs. For diesel engines, disconnect the high-pressure fuel lines from the injectors and move them aside.While doing so, do not allow them to be bent sharply (it is recommended to disconnect the fuel lines both from the injectors and from the high-pressure fuel pump).
3. If unit injectors are fitted, they must be removed before measuring compression.
4. On diesel engines with swirl-chamber mixture formation (pre-chamber diesels), it is sufficient to unscrew the glow plugs before measuring compression.
5. Turn the engine crankshaft with the starter or another drive mechanism (motor-generator, etc.) to remove carbon deposit particles, unburnt fuel, etc. from the engine cylinders.
6. Connect the compression gauge through a special adapter (supplied with the compression gauge) to the injector or glow plug openings.

Notes

• 1. The body of an injector that has reached the end of its service life may be used as an adapter. In this case the atomizer, springs and adjusting shims must be removed from it and the fuel return channel plugged. Insert the injector body into its standard seat and secure it, then connect the compression gauge to the high-pressure fuel line outlet.
• 2. Turn the engine with the starter or another drive mechanism (motor-generator, etc.) until the compression gauge pointer stops showing an increase in pressure. The crankshaft speed must not differ significantly from the starting speed of 150 — 250 rpm.
• 3. Record the compression gauge readings, then reset them using the valve and proceed to measure the remaining cylinders in the same way.

Points to watch

• When disconnecting the high-pressure fuel lines, do not allow them to be bent sharply.
• When turning the engine, the crankshaft speed must not differ significantly from the starting speed of 150 — 250 rpm.

Referenced by

• Industrial diesel engines
• Diesel engines with up to 30 l of oil
• Gasoline four-stroke engines

Source: Instructions for the use of XADO revitalizant gels IE-24.6-25612000-005-2008.