4.4. Measurement of degree of compression

Before measurements warm up the engine to working temperature. Thanks to it all mobile details will come to a working condition. Disconnect from plugs ignition (the plug 15), disconnect the tip of spark plugs and dismantle all candles. Establish a manual brake, the gear change lever put on idling, press coupling and accelerator pedals. Press a rubber cone of the controller of pressure to a candle aperture (in a diesel engine to an atomizer nozzle) the first cylinder – if necessary use the suitable adapter. The assistant turns the engine by means of a starter about 6–8 times. The maximum pressure is reached. An important point for carburettor engines: the best filling with a fresh fuel mix (external formation of a mix) is reached only by full pressing a gas pedal. Consider the indication of measurement and write down. In the presence of the device with записатором (the store of the data) switch it to the following cylinder.


The rubber cone компрессометра should close a candle aperture densely. On your command the assistant starts a starter. The starter should be turned until the device index will not be established in rest position.

Repeat process of measurements on all four cylinders of a number. It is important, that absolute value of pressure was identical in all cylinders.

Compression pressure decrease

If compression degree it (is heard) goes down, how shows experiment, it can be owing to following reasons:

In an inlet collector or the muffler of noise of an admission – not tight inlet valve. From an open radiator or a compensatory tank of a cooling liquid – a defective lining of a head of the block of cylinders or a crack in a head of the block of cylinders. From opened маслоналивной a mouth or the index of level of oil – the worn out walls of cylinders, working surfaces of cylinders or piston rings. In an exhaust pipe – not tight final valve.