Notes
(1) After the vehicle has been parked for a long time, engine oil may leak from the hydraulic valve clearance compensators, and air will enter the compensator high pressure chamber when the engine is started.
(2) After the vehicle has been parked for a long time, engine oil may drain from the oil supply port and it will take some time before engine oil is supplied to the hydraulic valve clearance compensators and air is forced out of the compensator pressure chambers.
(3) In any of these cases, the abnormal noise can be eliminated by bleeding the hydraulic valve lash adjusters.
1. Check the engine oil level and top up if necessary (pic. 3.13).
Pic. 3.13. The location of the marks on the dipstick for measuring the level of engine oil
Notes.
(1) If the engine oil level is too low, air is sucked through the oil filter and enters the lubrication passage to the hydraulic valve lifters.
(2) If the engine oil level is too high, the engine oil can foam up from the rotating crankshaft, causing a lot of air to enter the oil.
(3) If the quality of the oil deteriorates due to mixing with air, the air will be difficult to separate from the engine oil and its content in the oil will increase.
(4) If air mixed with engine oil is supplied to the high pressure chamber of the hydraulic valve gap adjuster, the air is compressed when the valve is opened, resulting in abnormal noise when the valve is closed (pic. 3.14). This phenomenon is analogous to increased valve clearance. The hydraulic valve clearance compensator recovers its performance after removing all air from the compensator high pressure chamber.
Pic. 3.14. Location of the high pressure chamber of the hydraulic valve clearance compensator
2. Start the engine and warm it up for 1-3 minutes while idling.
3. Carry out the cycles shown in Figure 3.15 with the engine running without load. Usually the abnormal noise is eliminated after repeating 10-30 cycles. However, if there is no noise change after 30 cycles, the noise may be caused by other engine problems.
Pic. 3.15. Cycles of changing engine operating modes when pumping hydraulic valve clearance compensators
4. After eliminating the abnormal noise, repeat the action shown in Figure 3.15 five more times.
5. To make sure that the abnormal noise is eliminated, let the engine idle for 1-3 minutes.