Glossary “compression valve” Definition:
Calibrated valve, located at the base of the shock absorber, providing variable resistance to fluid flow during compression (jounce).

Glossary “compression stroke” Definition:
Movement of the piston from BDC to TDC, immediately after the intake stroke. The upward movement of the piston squeezes the A/F mixture into the combustion chamber. In diesel applications, only air is compressed during this stroke. This is the second stroke in the four-stroke cycle.

Glossary “compression testing” Definition:
Test of the engine compression through the spark plug hole to determine if the pistomn and rings is sealing adequately.

Glossary “compression ring” Definition:
A piston ring that seals pressure during the compression and power strokes. There are usually two compression rings per piston.

Glossary “compression seal” Definition:
A metal seal found in a direct injection system, to resist compression pressures.

Glossary “compression height” Definition:
Distance, as measured from the crown of the piston to the center of the wrist pin.

Glossary “compression ignition” Definition:
Operating system of a diesel engine, where air, heated by compression is used to ignite the fuel.

Glossary “compression intake valve” Definition:
Term used for compression valve or intake valve.

Glossary “compression loaded ball joint” Definition:
Suspension ball joint, mounted above and positioned on the knuckle, so the vehicle weight forces the ball into the joint socket.

Glossary “compression ratio (CR)” Definition:
1). Measurement of volume compressed inside an engine cylinder. If compressed to 1/10 of its original volume, the compression ratio is 10 to 1. 2). The ratio of the volume in the engine cylinder with the piston at bottom dead center compared (BDC) to the volume at top dead center (TDC)

Glossary “compression braking” Definition:
Slowing of a vehicle restricting a diesel engine exhaust flow, such as that provided by a Jake brake. It is a misnomer that a gasoline engine will slow the vehicle by compression braking; actually, vacuum causes the braking effect.

Glossary “compression fitting” Definition:
Fittings that compress the end of a nut or a sleeve to provide a seal.

Glossary “compression gauge” Definition:
A gauge used in the spark plug hole of the cylinder head to measure cylinder compression pressures of a gas engine. Removing the glow plug from a diesel engine allows for the installation of higher pressure rated compression gauge used to measure cylinder compression.