101802 Checking for loss of pressure
WM 101802 Checking for loss of pressure
Tools
Preliminary work
1. Unscrew all spark plugs. -> 287020 Removing and fitting spark plugs Service and Repair
2. Position cylinder to be tested to ignition TDC and remove tool (dead centre finder).
2.1. The dead centre finder or "cylinder pipe" consists of a glass tube (inspection glass) with a piston -1- , hose and a rubber cone -2-.
Dead centre finder or "cylinder pipe"
2.2. The rubber cone is pressed onto the spark plug hole. The inspection glass is either held by a helper => Tool setup for dead centre finder or is secured vertically in a clearly visible position with a magnet.
Tool setup for dead centre finder
2.3. If the engine is now turned in direction of rotation on the crankshaft, the piston in the inspection glass is pressed up in the compression cycle => Piston up in order to go back down immediately upon reaching the TDC. The piston in the inspection glass stays down in overlapping TDC => Piston down.
Piston up
Piston down
Information
Test evaluation
- The test does not show any meaningful result on a new engine (i.e. one that hasn't been run in).
- A difference in pressure loss between the individual cylinders of approx. 5% is not significant.
- If the test shows an excessive loss of pressure (> 30%), a few drops of oil can be sprayed into the combustion chamber. Repeat the test. If the loss in pressure is now significantly less, the seal between the piston and cylinder is damaged.
- The air that is escaping causes hissing noises, which provide information about the component that is causing the damage.
If the limit values are exceeded, the engine must be started and the test repeated.
Testing pressure loss from the engine
WARNING
Rotating components
- Danger of limbs being trapped or severed
-> Do not reach into the danger area.
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 establish 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
Read the work steps and tips in the operating instructions for the Bosch tester before performing the pressure loss test. The described Bosch tester is used as an example for all suitable pressure loss testers. Details of calibration and use can be found in the relevant operating instructions.
1. Get the tester ready. Pressure loss tester Bosch EFAW 210 A WE 1066
2. Screw the test hose into the spark plug thread of cylinder 1 by hand (compression TDC) and tighten hand-tight.
Test hose
3. Connect the pressure loss tester to the compressed air system.
4. Adjust the scale. To do this, insert the test nozzle at the front into the device.
Adjusting the scale
5. Turn the adjusting wheel until the scale pointer is at the "cal." marking or "23%". The pressure is then equal in the two test chambers of the tool.
Adjusting wheel
6. Remove the test nozzle and check that the pointer falls back. Connect the test hose. The value that is displayed should not be greater than 25 %. If the loss in pressure is greater, it is safe to assume that the engine needs an overhaul.
Checking for loss of pressure
7. Interrupt the compressed air supply and unscrew the test hose.
8. Check the next cylinder by turning the crankshaft through another 90° and check the next cylinder in the firing order following the instructions provided.
V8 firing order: 1 - 3 - 7 - 2 - 6 - 5 - 4 - 8
Subsequent work
1. Remove the test hose once the test is complete.
2. Fit all spark plugs. -> 287020 Removing and fitting spark plugs Service and Repair