Vanos Seals Failure Affected Automobiles
Vanos BMW Repair kits
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BMW 6-cylinder Vanos Seals Solutions
Do you own one of the below BMW 6-cylinder cars, 1993-2006? If so then your vanos, engine variable valve timing unit, is most likely failing. These vanos units have been consistently diagnosed to fail due to deteriorating piston seal O-rings. The O-rings are made of a material that is failing in the engine environment. This causes the vanos piston seals to lose their sealing function and for the vanos unit to fail.
BMW does not provide the vanos seals separately. It sells rebuilt vanos units for ~$800. New rebuilt vanos units are supplied with the same failing O-rings and have been found to significantly fail in 20k miles (32k kilometers).
Vanos seals repair kits are now available. They incorporate upgraded O-rings to address the failure mode and replacement Teflon seal rings.
Vanos BMW Seals Failure Symptoms
Overall loss of torque and power, particularly in the lower RPM range, < 3k. Bogging then surging at 3k RPM. Uneven power distribution and RPM transition. Engine hesitations in the lower RPM range, < 3k. Louder idle and intermittent idle RPM hiccups. Difficult takeoffs. Loss of power and bogging when AC on. Increased fuel consumption. Vanos fault codes.
Double vanos cars with the M52TU engine (98/99-00) experience cold weather cold start idle jolts and possible stall.
Vanos Seals Repair Benefits
Overall increase in torque and power, particularly in the lower RPM range, < 3k. Resolution of bogging then surging at 3k RPM. Smooth even distribution of power and RPM transition. Resolution of engine hesitations in the lower RPM range, < 3k. Quiet stable idle. Smooth easy takeoffs. Improved performance when AC on. Reduced fuel consumption, by ~10%. Resolution of vanos fault codes.
Resolution of double vanos M52TU engine (98/99-00) cold weather cold start idle jolts and possible stall.
Rattle solution Vanos BMW
This vanos, like most vanos designs, can develop a rattle. The vanos rattle is caused by wear in the variable valve timing helical (slanted) gears. These gears are found on the camshaft, camshaft sprocket, and splined shaft which attaches to the vanos. The helical gear wear allows the camshaft to have lash movements that engage the splined shaft axially. At certain RPMs these movements resonate and engage axial play (free space) and cause associated components to hit and rattle. The axial play that facilitates the rattle is found on the helical gears and the vanos piston bearing. Replacing the helical gear components is expensive and the gears will wear again and the rattle will return. Removing the vanos piston bearing axial play significantly reduces the rattle to the point where it’s barely heard or not heard at all in the passenger compartment.
Removing the vanos piston bearing axial play significantly reduces the rattle. Also replacing the helical gear components (splined shaft, camshaft, sprocket) is expensive and the helical gears will wear again. Thus removing the vanos piston axial play is a practical approach to addressing the rattle problem. Furthermore, per bearing specification and consultation with bearings companies, there should be no bearing axial play and a notable axial pre-load (tightness) should be present.
The vanos piston bearing is made of a thick washer and two thrust (roller) bearings. The washer if mounted to the splined shaft and the two thrust bearings sandwich the washer facilitating the washer to rotate at camshaft speed. The washer and two thrust bearings are incased in a ring and two ring outer washers. The complete bearing is housed inside a piston cavity and is closed off with a piston bolt/cap.
Removing the bearing axial play requires modifying or replacing at least one bearing component. The thrust bearings are a standard part and are manufactured to tight tolerances. It’s not feasible to modify or replace them. The ring and center washer are non standard parts and are manufactured to loose tolerances. The ring height can be reduced or the center washer height can be increased to remove the bearing axial play. The ring has been found to have a large height variation and the washer has been found to have a smaller height variation. Due to these findings, it’s more effective to replace the ring. A bearing adjustment can be made at installation to address any minor axial fit variation.
The bearing ring and center washer were assessed by a metallurgical consulting firm. The parts were assessed for their material makeup, hardness including micro depth hardness, manufacturing process and finish.
As a solution to the vanos rattle problem a replacement vanos piston bearing ring is manufactured to the same specification as the original bearing ring but with a shorter height and a very tight height tolerance. The other ring dimensions are also manufactured to tight tolerances.
The bearing ring is a difficult and expensive component to manufacture. It’s made from a special bearing steel and hardened to a high hardness. All its surfaces are ground. This technique allows for machining hard parts to a high dimensional tolerance and a polished surface.