6-cylinder Single Vanos Rattle
Procedure
Vanos Repair
The following information is
provided for reference purposes only and should be used at your own risk
In no event shall Vanos-BMW.com 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 # 11361748036 (M50TU,
US S50) and 11361748819 (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. 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. 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.
Vanos-BMW.com 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 understand the cause of the vanos rattle some understanding
of the BMW variable valve timing system is needed.
Variable valve timing is the modifying of the engine valve opening/closing
timing dynamically. BMW’s variable valve timing implements a time shift (phase
shift) scheme. The camshaft cam is not modified, thus all the characteristics
of the opening and closing of the valve remain the same. What changes is the
time when the valve opening/closing occurs relative to the crankshaft timing. The
camshaft relative rotational position to the crankshaft is modified (shifted).
Advancing (clockwise) the camshaft advances (earlier) the valve timing
(opening/closing) relative to the crankshaft. Retarding (counter clockwise) the
camshaft retards (later) the valve timing (opening/closing) relative to the
crankshaft.
Helical (slanted) gears are utilized to physically implement this mechanism.
Due to their nature, helical gears require a rotation to insert onto each
other. This characteristic of helical gears is utilized to implement the
relative rotation of the camshaft to the crankshaft dynamically while the
engine is running.
[picture]
The camshaft and camshaft sprocket are not mounted directly to each other. The
sprocket has a hole at its middle that’s larger than the camshaft end. Opposing
slant helical gears are mounted at the sprocket hole and camshaft end. There is
an independent splined shaft with a cup and helical gears on the inside and
outside of the cup walls. The splined shaft cup inner helical gears match the
camshaft helical gears and the splined shaft cup outer helical gears match the
sprocket helical gears. The splined shaft cup is inserted onto and mates with the
camshaft and sprocket helical gears. Thus the splined shaft connects the
camshaft and sprocket. Inserting and withdrawing the splined shaft axially
in/out of the camshaft and sprocket requires the rotation of a component due to
the helical gears. The sprocket rotation is fixed by the timing chain. The
splined shaft can’t rotate due to the opposing helical gear slants on its cup
inside and outside. Thus it’s the camshaft that rotates when the splined shaft
is manipulated axially.
[picture]
Inserting the splined shaft axially onto the camshaft and sprocket causes the
camshaft to advance (rotate clockwise) and cause advanced (earlier) timing.
[picture]
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.
As the camshaft rotates the cam nose rolls onto the valve seat and compresses
the valve spring to open the valve and rolls off the valve seat and
decompresses the valve spring to close the valve. The resistance force of the
valve spring compression creates an opposing force to the forward rotation of
the camshaft. The recoiling force of the valve spring decompression creates an
additive force to the forward rotation of the camshaft.
Due to the splined shaft axial play, as the cam compresses the valve spring the
camshaft will slightly retard in relative rotation to the crankshaft and as the
cam decompresses the valve spring the camshaft will slightly advance in relative
rotation to the crankshaft. These movements of the camshaft are due to camshaft
least resistance path of movement. Due to the splined shaft axial play there is
less resistance to the camshaft retarding than compressing the spring and less
resistance to the camshaft advancing than containing the decompressing spring.
These movements manifest into camshaft lashes which engage the splined shaft
axially. The greater the helical gear wear the greater the splined shaft axial
play the stronger the camshaft lashes.
At certain engine RPMs these camshaft movements resonate. This causes stronger
camshaft lashes which cause more powerful engagements of the splined shaft
axially. This causes strong axial movements of the splined shaft. Any axial
play in the splined shaft vicinity is engaged and can cause a rattle.
There are two locations of axial play. The helical gears themselves have axial
play that’s engaged and rattles and the vanos piston bearing has axial play
that’s engaged and rattles.
Testing has been performed to assess and attempt to reduce the rattling. The
vanos piston bearing radial play was modified and the results indicated little
to no change in the rattling. The vanos piston bearing axial play was increased
and this resulted in a proportional increase in the rattling. The vanos piston
bearing axial play was decreased and this resulted in a proportional decrease
in rattling.
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 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.
The single vanos rattle repair kit includes one replacement vanos piston
bearing ring.
Repair techniques
To replace the piston bearing ring the piston bolt/cap that retains
the bearing must be removed. This is difficult due to the need to counter hold
the piston to open the bolt/cap and the bolt/cap head being only 3mm high.
The piston has fins that allow for counter holding the piston to open the
bolt/cap. But manufacturing a special tool for this purpose and providing it
for a one time use is cost prohibitive. A vice can be used to counter hold the
piston. A standard vise would damage the soft aluminum piston. Common aluminum
and rubber coated aluminum vise jaw liners would also risk damaging the piston.
Softer nylon vise jaw liners have been tested and found to hold the piston
effectively without the risk of damaging it. Soft vise jaw liners are provided
as an associate tool for the repair. The liners can also be useful for other
delicate component work.
A standard socket has chamfers (bevels) at the socket opening that widen the
opening to facilitate guiding the socket onto a bolt/nut head. Due to the
piston bolt/cap head being 3mm high, a standard socket will grab the bolt/cap head
with the opening chamfers. This has been found to cause the socket to slip and round
the bolt/cap head corners. Machining off the socket opening chamfers allows the
socket to have a tighter fit and improve the grab of the bolt/cap head. This
prevents the socket from slipping off the bolt/cap head.
A socket machined to remove the opening chamfers is provided as an associate
tool for the repair.
It has been found that first year model vanos units can have a 17mm or 18mm piston
bolt/cap head, while the remainder model years vanos units always have an 18mm
piston bolt/cap head. Thus for first year, 93, build cars both 17mm and 18mm
sockets should be acquired for the repair.
17mm and 18mm sockets are provided as associate tools for the repair.
Symptoms
Vanos rattle at a certain RPM range, often 1800-2200 RPM.
Rattle can also occur at idle.
This vanos is manufactured with a loose piston bearing. Thus all vanos units
can rattle. For the vanos to rattle a resonance needs to be achieved in the
camshaft lash and associate parts movements. Some car models are more
susceptible to achieving this resonance and rattle than others.
Models susceptible to experiencing vanos rattle:
3-series E36 all models
5-series E34 all models
Z3 all models.
This list will be updates as more data is collected.
Note: All models can and have experienced the vanos rattle.
Repair Procedure
The following is a single vanos piston bearing rattle repair
procedure.
This repair should be performed with the single vanos seals
repair. The rattle repair should be performed before the new vanos seals are
installed.
Single
Vanos Seals Procedure
If the car is a pre March 95 build E36 320i/325i/Euro 328i
or E34 520i/525i, then the intake sprocket diaphragm spring retrofit repair
should also be performed.
Single
Vanos Diaphragm Spring Procedure
Repair time: .5 hours mechanic, 1+ hours DIY.
Parts, Tools, and Shop Supplies
Single vanos rattle repair kit http://www.vanos-bmw.com/products.html, 18mm
socket - 1/2” drive
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 socket - 1/2”
drive
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 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 repeated insertion and withdrawal of splined
shaft in/out of piston.
Note: Radial play, side to side movement, is normal and necessary. This should
not be confused with axial play, in/out movement.
Attach soft vise jaw liners to vise jaws.
Place liner with horizontal V notch on vise inner jaw (picture left).
Place liner with vertical V notch and slanted V notch on vise outer jaw
(picture right).
Open vise jaws as far as necessary to insert 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.
Note: Cover bolt holes have a raised surface surrounding them.
Slightly loosen vise and rotate cover to orient cover flat surface at vise jaw
right side (picture).
Rotate cover to rest cover flat surface bolt hole rise on jaw liner right side
(picture).
With this orientation, cover left side bolt hole will be located at liner
horizontal V notch.
Note: Above cover orientation will cause cover right side bolt hole rise and
cover left side bolt hole rise to be counter held by vise jaw liner and prevent
cover from rotating when loosening 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.
Remove bearing center washer (magnet pickup).
Remove bearing bottom thrust (roller) bearing (magnet pickup).
Remove piston from 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 ring is stuck, place pick tip between ring inner bottom and bottom washer
and pry ring to break ring/washer seize (90 degree pick).
If ring tilts and binds in piston, press ring down to fully mount at bottom of
piston and repeat removal attempt. If necessary, hit ring down to break bind
and fully mount at bottom of piston (90 degree pick handle butt).
Set aside bearing ring 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: It is important bearing parts are thoroughly cleaned. This is needed to
properly assess new bearing 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 piston onto cover and splined shaft.
Insert piston onto splined shaft.
Hold down cover and press and rotate piston into cover.
Insert bearing bottom thrust (roller) bearing in piston bearing ring.
Note: Piston bearing top and bottom thrust bearings are interchangeable. Also
thrust bearing faces are functionally same thus thrust bearing can be inserted
in either orientation.
Insert bearing center washer in piston bearing ring.
Note: Center washer faces are same thus washer can be inserted in either
orientation.
Install bearing / splined shaft mounting bolt; left hand thread (T30
torx bit socket 1/4" / 1/4" ratchet).
Fully tighten, 8 Nm (6 ft-lb); left hand thread (T30 torx bit socket 1/4”
/ 3/8” torque wrench & 3/8” to 1/4" socket adapter).
Caution: Do not over tighten bolt. 8 Nm (6 ft-lb) is
slight torque.
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: Thrust bearing faces are functionally same thus thrust bearing can be
inserted in either orientation.
Insert bearing top washer on top of piston bearing ring.
Note: 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).
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.
Note: Cover bolt holes have a raised surface surrounding them.
Slightly loosen vise and rotate cover to orient cover flat surface at vise jaw
right side (picture).
Rotate cover to rest cover left side bolt hole rise on jaw liner left side
(picture).
With this orientation, cover right side bolt hole will be located at liner
horizontal V notch.
Note: Above cover orientation will cause cover left side bolt hole rise and
cover right side bolt hole rise to be counter held by vise jaw liner and
prevent cover from rotating when tightening 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: Axial fit cannot be properly assessed until piston bolt/cap is fully
tightened.
Note: Radial play, side to side movement, is normal and necessary. This should
not be confused with axial play, in/out movement.
If splined shaft binds and cannot be rotated then axial fit it too tight and
loosening adjustment is needed.
If splined shaft has any tilt movement then axial play is present and
tightening adjustment is needed.
Any level of resistance (pre-load) in splined shaft rotation indicates no axial
play and is considered 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.
Rotate washer 90 degrees and repeat sanding process.
Flip washer to opposite side and repeat above sanding procedure; 10 seconds
sanding, rotate 90 degrees, 10 seconds sanding.
Clean washer (brake cleaner & towels).
Reassemble piston bearing per above procedure and reassess bearing axial fit.
Note: Washer is made from hardened steel and does not easily wear. Sanding
procedure will remove ~.005mm washer height. Washer might need max .015mm
height adjustment.
Bearing tightening adjustment.
If splined shaft has any tilt movement then axial play is present and
tightening adjustment is needed.
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. Perform sanding for 10 seconds.
Rotate ring 90 degrees and repeat sanding process.
Flip ring to opposite side and repeat above sanding procedure; 10 seconds
sanding, rotate 90 degrees, 10 seconds sanding.
Clean ring (brake cleaner & towels).
Reassemble piston bearing per above procedure and reassess bearing axial fit.
Note: Ring is made from hardened steel and does not easily wear. Sanding
procedure will remove ~.005mm ring height. Ring might need max .015mm height
adjustment.
Once piston bearing fit is assessed and adjustment is
performed if needed, spray oil into piston bearing (oil spray).
Center hole in piston bolt/cap facilitates access for oil spray.
Rotate splined shaft to distribute oil in bearing.
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