Checking Pressure Loss Of Cylinders

Information 

• The check for loss of pressure can be used to assess the mechanical condition of a combustion engine. 
• A pressure loss test is more meaningful than the compression pressure check. 
• The percentage leakage quantity can be used to determine whether the leaks in the combustion chamber in question are so large that the combustion chamber must be repaired. 
• The worn components (e.g. piston rings) can be identified by the compressed air that is escaping. 

Information 

The piston must be exactly at the upper return point when checking pressure loss. Do not touch any components of the belt drive and do not put any tools on the crankshaft pulley while performing the check.

Information 

The pictures shown in this document may differ from the original.

Information 

The dead centre finder or "cylinder pipe" consists of a glass tube (inspection glass) with a piston -1-  , hose and a rubber cone -2-  .

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Dead centre finder - "cylinder pipe"

1. Press the rubber cone of the dead centre finder from tool set > VAS 522 001 - pressure loss tester  onto the spark plug hole. The inspection glass must either be held by a helper > Tool setup - dead centre finder  or secured vertically in a clearly visible position with a magnet.

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   Tool setup - dead centre finder

2. Continue to turn the engine in direction of rotation using > T40263 - wrench, 21 mm  and > T40314 - adapter  . This presses up the piston in the inspection glass in the compression cycle. > Top piston 

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   Top piston

3. Immediately after reaching the TDC position, the piston moves down again. The piston in the inspection glass stays down in overlapping TDC. > Bottom piston 

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   Bottom piston

4. Move the cylinder to be checked to ignition TDC and remove dead centre finder from tool set > VAS 522 001 - Pressure loss tester  .

   Information 

   Read the work steps and tips in the attached operating instructions before starting the pressure loss test. The device described here is used as an example for all suitable pressure loss testers. Details of calibration and use can be found in the relevant operating instructions.

5. > VAS 522 001 - Pressure loss tester  must be ready.
6. Screw the test hose into the spark plug thread of cylinder 1 by hand (compression TDC) and tighten hand-tight.

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   Test hose

7. > VAS 522 001 - Pressure loss tester  must be connected to the compressed air system.
8. Insert test nozzle at the front into the device.

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   Test nozzle

9. Adjust the scale.

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   Adjusting wheel

   1. 9.1 Turn the adjusting wheel until the pointer on the scale is at the cal.  marking or 23%  .

   Information 

   The value that is displayed should not be greater than 25%. If the pressure loss is greater, it is safe to assume that the engine needs an overhaul.

10. Remove test nozzle and check that the pointer falls back. Then connect the test hose.

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    Checking for loss of pressure

11. Interrupt the compressed air supply and unscrew the test hose.
12. To check the next cylinder:

Continue to turn the engine in direction of rotation using > T40263 - wrench, 21 mm  and > T40314 - adapter  .

For V6 engines:  Turn the crankshaft through another 120° and check the next cylinder in the firing order according to the specified steps.

For V8 engines:  Turn the crankshaft through another 90° and check the next cylinder in the firing order according to the specified steps.