Renault Megane, Scenic

Since 1996 of release

Repair and car operation

Compression check - the description

As a result of check of a compression you can estimate a condition of such elements of the engine as pistons, rings, valves, a lining of a head of the block of cylinders. The compression can be low because of the leak caused by deterioration of piston rings, faulty valves and their saddles, or the burnt through lining of a head of the block of cylinders.

The engine should be heated-up to normal working temperature, and the accumulator should be completely charged.

CHECK

1. Clear area round spark plugs to prevent dirt hit in cylinders. 2. Remove all spark plugs from the engine (address to Section Replacement of spark plugs and check of system of ignition). 3. Disconnect low-voltage conducting from the block of management of amplifiers ignitions (engine E7J), or from the coil ignitions (engine K7M). Also put out of action a control system of the engine, having removed the fuse of protection of the engine from the block of safety locks in an impellent compartment (a safety lock "M" on the scheme of electric connections 1), but pay attention that through this safety lock a food on the mechanism of an emergency tension of a seat belt and system of a pillow of safety moves, therefore also look notes and preventions in Section System of a tension of seat belts of forward seats - the general information, and in Sections System of pillows of safety - the general information and safety measures and Removal and installation of components of pillows of safety. 4. Establish a manometre in an aperture of a spark plug №1. 5. Ask the assistant to keep pressed against the stop a gas pedal, simultaneously some times having turned the engine a starter. Observe of manometre indications - the compression should grow in the serviceable engine quickly. The low compression on the first turn and the subsequent its gradual increase specifies in deterioration of piston rings. If the compression remains low, valves or a lining of a head of the block of cylinders have burnt through, or the head has burst. The deposit formed on undersides of heads of valves, also can be at the bottom of a low compression. 6. Add a little impellent oil in each cylinder, through an aperture for a spark plug, and repeat test. 7. If after that the compression for a while increases, the cylinder or the piston are worn out. Absence of improvement specifies that, probably, there is a leak through the burnt valves or the burnt through lining of a head of the block of cylinders. 8. The low compression in two adjacent cylinders almost is for certain caused by that between them the lining of a head of the block of cylinders has burnt through. Presence of a cooling liquid at impellent oil will confirm it. 9. Values of a compression for the engines described in this management are not defined by the manufacturer. However on the basis of the information presented in the previous paragraphs, it is possible to define an engine condition.