PRE-RELEASE
Hydraulic tappets
| Hydraulic tappets |
| Description |
The valve gear incorporates hydraulic tappets which balance the valve clearance within a limited working range of 2.05 mm (0.081 in). This range is within 18.75 - 20.8 (0.738-0.819 in) from the camshaft towards the position of the valve.
The valve tappet has two storage chambers and one high-pressure chamber, which is sealed from one of the storage chambers with a spring-loaded ball valve. A return spring in the high-pressure chamber acts on the sliding plunger so that any clearance between the tappet and the base circle of the cam is eliminated. At the same time, the high-pressure chamber expands to compensate for the oil volume lost through leakage in the gap between the plunger and cylinder that occurs at collaring pressure. Under various conditions the hydraulic tappets may give rise to noise (rattling of varying intensity). In most cases, this noise is of a temporary nature and does not require remedial action.
Below is a description of the most common types of noise, their probable cause and any preliminary action that needs to be taken.
| Valve noise |
| 1. |
Valve chatter after long-term parking (longer than 48 hours).
During prolonged parking, the oil drains out of the tappets' high-pressure chambers and air is forced in. Once the engine is started, it will take approx. 15 minutes for the air to be purged from the tappets. During this time, valve noise will be heard (chatter). The engine speed should not be allowed to exceed 3000 rpm until the valve chatter has ceased. See 4. |
|
| 2. |
Valve chatter on starting the engine after an oil change.
If valve chatter did not occur before the oil change, it will disappear of its own accord when the engine oil pressure has reached normal level. |
|
| 3. |
Temporary noise on starting a cold engine.
This noise is perfectly normal and will disappear of its own accord when the engine oil pressure has reached normal level. |
|
| 4. |
Valve chatter if the engine is started after performing work on the engine that has involved turning over the engine manually or with the starter motor.
The noise is due to one or more tappets being drained of oil. The noise will cease after being driven for a while. In severe cases, it may take up to 15 minutes at 2000-3000 rpm. At lower engine speeds, it will take much longer to expel the air and at higher speeds, there is a danger of damaging the valve tappets. |
|
| 5. |
Noise after changing valve tappets.
Cause and remedy, see 4. |
|
| 6. |
Noise occurring after a short period at idling speed with warm engine. If the engine is kept at 1500 rpm or above, the noise will soon cease.
The noise is due to low oil pressure in the hydraulic tappets at idling speed. |
|
| 7. |
Noise occurring at high engine speeds, which disappears after a period at idling speed.
This noise is due to a high concentration of air in the oil at high engine speeds. The air originates from leakage on the suction side of the oil pump, e.g. a leak in the suction pipe. |
|
| 8. |
Noise from individual tappets independent of how the car is driven.
The probable cause is an impurity trapped in the tappet's non-return valve. The defective tappet (tappets) can be most easily detected once the engine has been turned off and the camshaft cover removed by pressing all the unloaded tappets. The tappet that feels soft (spongy) is the defective one. Change the defective tappet (tappets). |
|
