6-cylinder Single Vanos Rattle Procedure
The following information is provided for reference purposes only and should be used at your own risk Single Vanos Rumble
In no event shall Beisan Systems, LLC or its members be liable for incidental, consequential, or special loss or damages of any kind however caused.
Introduction
“Vanos” is BMW’s name for its variable valve timing units. Vanos units take on various shapes and design according to car year and model (engine model). The vanos discussed here is BMW part # 11-36-1-748-036 (M50TU, US S50) and 11-36-1-748-819 (M52, S52). It’s a single vanos, meaning only the intake valve timing is varied. This vanos unit is part of BMW 6-cylinder engines M50TU, M52, US S50, S52. These engines were incorporated into a wide range of car models during years 1993-1999. They are found in the 3-series E36 93-97, 5-series E34 93-95 / E39 96-98, 7-series E38 95-98, Z3 Roadster 2.8 E36 96-98, EU Z3 Coupe 2.8 E36 96-98, US M3 E36 94-99, US Z3 M E36 98-99.
This vanos, like most vanos designs, can develop a rattle. Wear in the variable valve timing helical (slanted) gears causes the Vanos rattle.You can find these gears 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 helical gears and Vanos piston bearing contain the axial play that facilitates the rattle.
Replacing the helical gear components is expensive and the gears will wear again and the rattle will return. Removing the Vanos piston bearing’s axial play significantly reduces the rattle, making it barely audible or completely silent in the passenger compartment.
Performance cams like the cams on the M3 or aftermarket performance cams (Schrick/Sunbelt) create stronger camshaft lash forces and thus are more susceptible to causing a rattle.
Beisan Systems provides a vanos rattle repair kit which has a replacement component for the vanos piston bearing to remove the bearing axial play. Associate special tools are also provided to facilitate the repair.
Below is a more detailed explanation of the rattle cause and solution.
Technical background
To grasp why the Vanos rattle occurs, it’s essential to first understand how BMW’s variable valve timing system works.
Variable valve timing dynamically adjusts the timing of engine valve opening and closing. BMW’s system uses a phase shift mechanism, meaning it shifts the timing rather than altering the camshaft lobes. As a result, the valve’s opening and closing characteristics remain unchanged, but the timing of these events shifts relative to the crankshaft.
- Advancing the camshaft (rotating it clockwise) causes the valves to open and close earlier relative to the crankshaft.
- Retarding the camshaft (rotating it counterclockwise) delays the valve timing, making the valves open and close later.
Role of Helical Gears in Variable Timing
Helical (slanted) gears enable this phase shift mechanism. Due to their design, helical gears require rotational movement to engage or disengage. This characteristic allows for real-time adjustments to the camshaft’s rotation relative to the crankshaft while the engine is running. The camshaft and camshaft sprocket are mounted separately, rather than being directly connected. The sprocket has a central hole that is larger than the camshaft end. Opposing slant helical gears on the sprocket hole and the camshaft end allow movement.
Function of the Splined Shaft
An independent splined shaft—featuring a cup with helical gears on both its inner and outer walls—connects the camshaft and sprocket:
- The inner helical gears of the splined shaft match those on the camshaft.
- The outer helical gears of the splined shaft match those on the sprocket.
- This configuration allows the splined shaft to act as a link between the camshaft and the sprocket.
Since helical gears require rotation for axial movement, inserting or withdrawing the splined shaft causes a rotational response. The timing chain holds the sprocket in a fixed position, preventing it from rotating. The splined shaft itself also cannot rotate due to the opposing helical gear slants inside and outside the cup. As a result, axial movement of the splined shaft forces the camshaft to rotate, adjusting the valve timing dynamically
Inserting the splined shaft axially onto the camshaft and sprocket causes the camshaft to advance (rotate clockwise) and cause advanced (earlier) timing.
Withdrawing the splined shaft axially from the camshaft and sprocket causes the camshaft to retard (rotate counter clockwise) and cause retarded (later) timing.
The vanos is a hydraulic actuator. Its function is to dynamically position the splined shaft axially to cause camshaft advance or retard rotation which enacts variable valve timing.
The vanos utilizes two cylinders and a piston. There is an oil chamber at the fore and aft of the piston. Controlling the oil pressure in the two oil chambers manipulates the axial position of the piston.
Seals on the piston allow the piston to reciprocate axially along the cylinder walls while maintaining a tight oil seal on the two oil chamber. The splined shaft is mounted to the vanos piston. Thus manipulating the axial position of the piston also manipulates the axial position of the splined shaft. The piston has a bearing at its center. The splined shaft is mounted to this bearing. The piston bearing allows the splined shaft to rotate with the camshaft and sprocket while not rotating the piston.
Cause of rattle
Due to the nature of helical gears, not only does the axial positioning of the splined shaft cause the rotation of the camshaft, but also reciprocally the rotation of the camshaft causes the axial positioning of the splined shaft.
Over time and use the helical gears on the camshaft, sprocket, and splined shaft develop wear along the gear spline side contact surfaces. This wear creates excessive play between the helical gears. This causes excessive play in the fit of the splined shaft to the camshaft and sprocket. This manifests in axial play between the splined shaft and camshaft and sprocket.
The testing results show that removing the vanos piston bearing axial play significantly reduces the rattling.
Some owners have had the dealership replace their helical gears (splined shaft, camshaft, sprocket) and this resolved all the rattle. These owners eventually developed the rattle again and to the same level as before. This is due to the new helical gears wearing and creating the splined shaft axial play.
Engines with higher lift (performance) cams are more susceptible to having a vanos rattle, and the rattle is likely to be worse. The higher lift cams compress the valve springs further and thus cause higher spring forces. This causes stronger camshaft lashes which engage the splined shaft and axial play components harder.
This affects M3 cars and cars with aftermarket performance cams (Schrick/Sunbelt).
Rattle solution
As noted above 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 consists of a thick washer and two thrust (roller) bearings. The washer mounts to the splined shaft, and the thrust bearings sandwich it, enabling the washer to rotate at camshaft speed.
A ring and two outer washers encase the washer and thrust bearings, forming the complete bearing assembly. This assembly sits inside a piston cavity and is sealed with a piston bolt/cap.
To eliminate bearing axial play, you must modify or replace at least one bearing component. Since manufacturers produce thrust bearings with tight tolerances as standard parts, modifying or replacing them is not practical. However, the ring and center washer are non-standard parts with looser tolerances, making them suitable for adjustment.
Reducing the ring’s height or increasing the center washer’s height can remove axial play. Analysis has shown significant height variation in the ring, while the center washer exhibits less variation. Therefore, replacing the ring is the most effective solution. A bearing adjustment during installation can further refine the axial fit.
A metallurgical consulting firm assessed the bearing ring and center washer, examining their material composition, hardness (including micro-depth hardness), manufacturing process, and finish.
To address the vanos rattle issue, a replacement vanos piston bearing ring is produced with the same specifications as the original but with a reduced height and significantly tighter height tolerance. Other ring dimensions are also manufactured with strict tolerances.
Manufacturing the bearing ring is a complex and costly process. It is made from a specialized bearing steel, hardened to a high level, and ground on all surfaces. This grinding technique enables precision machining of hardened parts, ensuring high dimensional accuracy and a polished surface.
The single vanos rattle repair kit includes one replacement vanos piston bearing ring.
Repair techniques
To replace the piston bearing ring, remove the piston bolt/cap that retains the bearing.
This process is challenging because the piston must be counter-held while loosening the bolt/cap, and the bolt/cap head is only 3mm high.
The piston has fins designed for counter-holding during removal. However, manufacturing and providing a specialized tool for this one-time use is not cost-effective. Instead, a vise can be used to counter-hold the piston. Since a standard vise could damage the soft aluminum piston, common aluminum or rubber-coated jaw liners also pose a risk. Testing has shown that softer nylon vise jaw liners effectively hold the piston without causing damage. These soft jaw liners come as an auxiliary tool for the repair and are also useful for handling other delicate components.
A standard socket has chamfers (bevels) at the opening to guide it onto a bolt or nut head. Since the piston bolt/cap head is only 3mm high, these chamfers prevent a proper grip, causing the socket to slip and round off the bolt/cap head corners. Removing the socket’s opening chamfers results in a tighter fit, ensuring a secure grip and preventing slippage. A modified socket with chamfers removed is included as an auxiliary tool for this repair.
Early-production vanos units from the first model year may have either a 17mm or 18mm piston bolt/cap head, whereas later models consistently use an 18mm head. For 1993-built vehicles, both 17mm and 18mm modified sockets may be required. Therefore, the repair kit includes both 17mm and 18mm modified sockets as auxiliary tools.
Single Vanos Diaphragm Spring Procedure
Repair time: .5 hours mechanic, 1+ hours DIY.
Parts, Tools, and Shop Supplies
Single vanos rattle repair kit (BS012) $30/each (www.beisansystems.com), 18mm modified socket – 1/2” drive (BS093) $5/each (www.beisansystems.com), soft vise jaw liners (BS091) $15/each (www.beisansystems.com)
Note: If car model year is 93 (first year of single vanos), vanos piston bolt/cap can be 17mm or 18mm, thus also acquire 17mm modified socket – 1/2” drive (BS092) $5/each (www.beisansystems.com)
Caution: Beisan soft vise jaw liners are critical to performing repair. They are fully nylon and will allow tightening vise without damaging piston apparatus. Other types of jaw liners, including aluminum and rubber coated aluminum, can damage piston apparatus. Beisan liners also incorporate horizontal V notch which allows trapping cover bolt hole rise and keeping cover from slipping.
Caution: Beisan modified socket is critical to performing repair. It is machined to remove opening champers. A standard socket will have chamfers which will cause socket to slip and damage piston bolt/cap head.
4”, or larger, swivel vise (Harbor Freight, 4” at store $45)
Note: Vise must be mounted for use.
1/2″ long-arm ratchet, 1/4″ ratchet, 3/8″ torque wrench w/ reverse function (8 Nm [6 ft-lb], 40 Nm [30 ft-lb])
Magnet pickup, 90 degree pick tool
T30 torx bit socket 1/4″, 3/8” to 1/4″ socket adapter, 3/8” to 1/2″ socket adapter
Not shown: Heat gun (or alternate heating device)
Paper towels, brake cleaner, oil spray
~400 grade sandpaper (not shown)
Repair
Repair is performed once vanos is removed from engine and vanos cylinder cover is removed. Refer to single vanos repair procedure, Single Vanos Seals Procedure
Replace vanos piston seals after this procedure.
If vanos piston bolt/cap is 17mm, replace all references in procedure for 18mm to 17mm.
Removal of piston bearing
Clean vanos piston apparatus; piston, cover, splined shaft (brake cleaner & towels).
Inspect piston bearing axial play.
Hold piston and tilt (rock) splined shaft to each side to note bearing axial play (free space).
Axial play can also be checked by repeatedly inserting and withdrawing the splined shaft from the piston.
Note: Radial play (side-to-side movement) is normal and necessary. Do not confuse this with axial play (in-and-out movement).
Attach soft vise jaw liners to the vise jaws.Place the liner with the horizontal V-notch on the inner vise jaw (see picture, left).Then, position the liner with the vertical V-notch and slanted V-notch on the outer vise jaw (see picture, right).Finally, open the vise jaws as needed to insert the Vanos piston and cover vertically (see next picture).
Press piston and cover together.
Insert piston apparatus in vise vertically with piston at vise outer jaw.
Rest piston center rim on jaw liner at center and lightly tighten vise to hold piston apparatus.
Slightly loosen the vise and rotate the cover so that its flat surface aligns with the right-side vise jaw (see picture).Next, adjust the cover so that the raised bolt hole on the flat surface rests on the right-side jaw liner (see picture).In this position, the left-side bolt hole will align with the liner’s horizontal V-notch.
Note: The above cover orientation ensures that the cover’s right-side bolt hole rise and left-side bolt hole rise are counter-held by the vise jaw liner, preventing the cover from rotating while loosening the piston bolt/cap.
Strongly tighten vise.
Note: Vise jaw liners are soft and will not damage piston and cover surfaces.
Caution: Do not clamp on piston apparatus without use of soft (nylon) vise jaw liners. Other types of jaw liners, including aluminum and rubber coated aluminum, can damage piston apparatus.
Loosen (break seize) piston bolt/cap (18mm modified socket 1/2” / 1/2” long-arm ratchet).
Hold in tool at bolt/cap (hand). Bolt/cap head is short and tool can dislodge.
If piston or cover rotate in vise jaws reposition piston apparatus per above instructions and strongly tighten vise.
If bolt/cap difficult to loosen apply heat to bolt/cap thread area (heat gun or alternate heating device)
Note: Do not further loosen piston bolt/cap at this time.
Once piston bolt/cap loosens (seize breaks), loosen vise and remove piston apparatus from vise.
Insert splined shaft vertically in vise and tighten vise jaws onto splined shaft.
Note: Specific position of splined shaft in vise is not significant.
Remove piston bolt/cap (18mm modified socket 1/2” / hand).
Remove bearing top washer (magnet pickup).
Note: Washer is often bound to bolt/cap with oil and comes off with bolt/cap.
Remove bearing top thrust (roller) bearing (magnet pickup).
Remove bearing / splined shaft mounting bolt; left hand thread (T30 torx bit socket 1/4″ / 1/4″ ratchet).
Caution: Bearing/splined shaft mounting bolt is left hand thread. Turn clockwise to remove.
Take out the bearing center washer (magnet pickup).
Next, remove the bearing bottom thrust (roller) bearing (magnet pickup).
Finally, detach the piston from the cover and splined shaft.
Hold down cover and pull up and rotate piston to remove from cover and splined shaft.
Place piston on table top.
Remove bearing outer ring.
Clean bearing ring while still mounted in piston (brake cleaner & towels).
Insert right and left index fingers into bearing ring. Press against ring inner right and left walls and wiggle and pull ring out of piston.
If the ring is stuck, use a 90-degree pick to insert the tip between the ring’s inner bottom and the bottom washer, then pry gently to break the ring/washer seizure. Should the ring tilt and bind within the piston, press it down to fully seat it at the bottom before attempting removal again. When needed, tap the ring down with the butt of the 90-degree pick handle to release the bind and ensure it is fully seated.
Set the bearing ring aside, as it will not be reinstalled.
Remove bearing bottom washer.
Place pick tip between washer inner bottom and piston and pry washer out (90 degree pick).
Note: Washer is difficult to perceive until removed.
Cleaning of parts
Clean bearing parts (brake cleaner & towels).
Note: Thoroughly clean all bearing parts to ensure an accurate assessment of the new bearing’s axial fit.
Clean piston bearing cavity and bolt/cap (brake cleaner & towels).
Installation of piston bearing
Bearing parts installation sequence from right to left.
Bearing parts from left to right: Bolt/cap, top washer, top thrust bearing, bolt, center washer, bottom thrust bearing, ring, bottom washer.
Insert bearing bottom washer in piston (fingers).
Note: Piston bearing top and bottom washers are interchangeable. Also washer faces are same thus washer can be inserted in either orientation.
Manipulate washer side to side while slightly pressing down to fully insert (fingers).
Insert new bearing outer ring in piston (fingers).
Note: New ring is marked “BS” on outer perimeter.
Initially insert ring in piston.
Insert right and left index fingers into ring. Press fingers against ring inner right and left walls and manipulate ring side to side while slightly pressing down to facilitate ring full insertion.
Rotate piston 90 degrees and repeat ring insertion to verify full insertion.
Note: Ring should fully mate with bottom washer (picture).
Remount the piston onto the cover and splined shaft. Next, insert the piston onto the splined shaft. While holding down the cover, press and rotate the piston into place.
Insert bearing bottom thrust (roller) bearing in piston bearing ring.
Note: Piston bearing top and bottom thrust bearings are interchangeable. The thrust bearing faces are functionally identical, allowing installation in either orientation.
Insert bearing center washer in piston bearing ring.
Note: The center washer faces are identical, allowing installation in either direction.
Install the bearing/splined shaft mounting bolt using a left-hand thread (T30 Torx bit socket, 1/4″ ratchet).Then, fully tighten the bolt to 8 Nm (6 ft-lb) using a left-hand thread (T30 Torx bit socket, 3/8” torque wrench, and a 3/8” to 1/4″ socket adapter).
Hold piton and loosen vise jaws.
Lower piston and cover and rest them on top of vise jaws.
Note: Splined shaft will suspend from piston and bearing center washer will drop down some into bearing ring (pictures).
Insert bearing top thrust (roller) bearing in piston bearing ring.
Note: The thrust bearing faces are functionally identical, allowing insertion in either orientation,
Insert bearing top washer on top of piston bearing ring.
Note: The washer faces are also identical, so it can be inserted in either direction. Manipulate washer side to side while slightly pressing down to fully insert (fingers).
Install piston bolt/cap.
Counter hold piston and tighten bolt/cap (18mm modified socket 1/2” / hand).
Only hand tighten bolt/cap.
Loosen vise jaws and remove piston apparatus.
Open vise jaws as far as necessary to insert piston and cover vertically (see next picture).
Press piston and cover together.
Insert piston apparatus in vise vertically with piston at vise outer jaw.
Rest piston center rim on jaw liner at center and lightly tighten vise to hold piston apparatus.
First, slightly loosen the vise and rotate the cover to position its flat surface against the right side of the vise jaw (see picture).Next, rotate the cover so that the raised left-side bolt hole rests on the left-side jaw liner (see picture).In this orientation, the right-side bolt hole will align with the liner’s horizontal V-notch.
Note: The above cover orientation will ensure that the left and right side bolt hole rises are counter-held by the vise jaw liner, preventing the cover from rotating while tightening the piston bolt/cap.
Strongly tighten vise.
Note: Vise jaw liners are soft and will not damage piston and cover surfaces.
Caution: Do not clamp on piston apparatus without use of soft (nylon) vise jaw liners. Other types of jaw liners, including aluminum and rubber coated aluminum, can damage piston apparatus.
Fully tighten piston bolt/cap, 40 Nm (30 ft-lb) (18mm modified socket 1/2” / 3/8” torque wrench & 3/8” to 1/2″ socket adapter).
Hold in tool at bolt/cap (hand). Bolt/cap head is short and tool can dislodge.
If piston or cover rotate in vise jaws reposition piston apparatus per above instructions and strongly tighten vise.
Once piston bolt/cap fully tightens, loosen vise jaws and remove piston apparatus from vise.
Inspection and adjustment of piston bearing
Inspect piston bearing axial play.
Hold piston and rotate splined shaft to note resistance to rotation.
Hold piston and tilt (rock) splined shaft to each side to note bearing axial play (free space).
Note: You cannot properly assess axial fit until you fully tighten the piston bolt/cap.Note: Radial play, or side-to-side movement, is normal and necessary. Do not confuse this with axial play, or in/out movement.If the splined shaft binds and you cannot rotate it, the axial fit is too tight and you need to loosen it. If the shaft exhibits any tilt movement, axial play is present and requires tightening. Any resistance (pre-load) in the splined shaft rotation indicates the absence of axial play, which is an optimal fit.
Note: M3 cars and cars with aftermarket performance cams (Schrick) must have no bearing axial play and bearing should have resistance to rotation (pre-load) to achieve optimal results.
Bearing loosening adjustment.
If splined shaft binds and cannot be rotated then axial fit it too tight and loosening adjustment is needed.
Disassemble piston bearing per above procedure.
Place sandpaper (~400 grade) on flat table top. Place bearing center washer on sandpaper.
Slide washer side to side on sandpaper ~6” back and forth while moderately pressing washer on sandpaper. Perform sanding for 10 seconds.
First, rotate the washer 90 degrees and repeat the sanding process. Then, flip the washer to the opposite side and follow the same sanding procedure: sand for 10 seconds, rotate 90 degrees, and sand for another 10 seconds. After sanding, clean the washer thoroughly using brake cleaner and towels. Finally, reassemble the piston bearing according to the previous procedure and reassess the bearing’s axial fit.
Bearing tightening adjustment.
If the splined shaft tilts, axial play is present and requires a tightening adjustment. Disassemble piston bearing per above procedure.
Place sandpaper (~400 grade) on flat table top. Place bearing ring on sandpaper.
Slide ring side to side on sandpaper ~6” back and forth while moderately pressing ring on sandpaper. First, perform sanding for 10 seconds. Then, rotate the ring 90 degrees and repeat the sanding process. Next, flip the ring to the opposite side and follow the same sanding procedure: sand for 10 seconds, rotate 90 degrees, and sand for another 10 seconds. After sanding, thoroughly clean the ring using brake cleaner and towels. Finally, reassemble the piston bearing according to the previous procedure and reassess the bearing’s axial fit.
After assessing the piston bearing fit and making any necessary adjustments, spray oil into the piston bearing.
Center hole in piston bolt/cap facilitates access for oil spray.
Rotate splined shaft to distribute oil in bearing.
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