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"Troubleshooting BMW Hydraulic Bucket Tappet Problems
Common complaints of BMW hydraulic bucket tappets (HVA) are tapping/rattling noise from the valve train area or a binding HVA element.
The two most common reasons for the replacement of BMW hydraulic bucket tappets (HVA) found in M42, M44, M50, M52, M54, M60, M62, S50, S52 and S62 engines are: tapping/rattling noise from the valve train area or a binding HVA element. Tapping/rattling noise from the valve train area may have various different causes depending on engine oil level, engine/oil temperature, when the noise is heard (cold start, engine hot), etc.
The following Complaint/Cause and Repair scenarios will assist in troubleshooting for HVA element noise:
Situation 1A
Tapping / rattling noises from the area of the valve train up to 20 seconds after a cold start.
Cause
These noises can be traced back to the higher viscosity of cold mineral based engine oil. For a brief moment insufficient oil reaches the high pressure chamber ofthe HVA element via the high pressure valve after start up. This results in clearance between the HVA element and the camshaft lobe which then causes a tapping/rattling noise.
Influencing factors for this complaint:
• Viscosity of engine oil used
• Ambient temperature
This condition is not caused by mechanical damage to any engine components and has no damaging effect on the service life ofthe engine.
Repair
Check that oil viscosity is matched to ambient temperature range at which the vehicle is being operated. Refer to Temperature/Viscosity chart for further information.
Situation 1B
Tapping/rattling noises in the area of the valve train for the first 8 -10 consecutive cold starts. This condition usually occurs after the engine has been turned off at normal operating temperature and then not warmed up to full operating temperature during the next series of cold starts. This operating condition can occur, for example, on new vehicles.
Cause
Hot engine oil initially escapes from the oil galley of the HVA elements when the engine is stopped. A small amount of oil also escapes through the gaps between the HVA elements and the HVA housings in the cylinder head.
The oil then contracts while the engine is cooling down and allows air to enter the oil system. During the subsequent cold start, this air can be forced into the HVA elements (causing air pockets) through the build up of engine oil pressure. The resulting clearance between the HVA elements and the camshaft lobes causes the tapping/rattling noises.
This HVA tapping/rattling noise is not dependent on the amount oftime the engine is off, but rather on:
• The temperature of the engine when it was turned off (operating temperature - hot)
• The number of subsequent cold starts without the engine being warmed up to operating temperature.
Repair
Run the engine to dissipate (bleed) the air trapped in the high pressure chamber of the HVA elements.
