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Introduction

BMW introduced its first variable valve timing systems in 93. It called its variable valve timing unit “vanos”. On the standard i6 engine this was a single vanos (intake adjustment) and was initially introduced on car models E36 320i/325i and E34 520i/525i. BMW soon realized its variable valve timing system was prone to a rattle. It modified the system to incorporate a diaphragm spring on the intake camshaft sprocket. The diaphragm spring dampens sprocket rotational play and thus reduces the rattle. This diaphragm spring design was incorporated in all subsequent standard i6 single vanos car models, except the Euro 328i. On March 95 build the diaphragm spring design was introduced on the E36 320i/325i/Euro 328i and E34 520i/525i.
This diaphragm spring design can be retrofitted onto pre March 95 build E36 320i/325i/Euro 328i and E34 520i/525i cars. This retrofit can significantly reduce the variable valve timing system rattle.

Technical background

To understand the function of the diaphragm spring for reducing the 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.

On a non variable valve timing engine the camshaft sprocket is mounted directly to the camshaft. As noted above with the BMW variable valve timing system the sprocket is connected to the camshaft via the splined shaft. But this is not sufficient to fully support the sprocket. BMW devised a method to mount the sprocket on the camshaft but still allow the camshaft to rotate independent of the sprocket for variable valve timing adjustment.
The camshaft has three dowels protruding axially and the sprocket has three slots along its face. The sprocket slots are inserted onto the camshaft dowels. When the camshaft is rotated for timing adjustment the camshaft dowels slide along the sprocket slots. This allows the camshaft to rotate independent of the sprocket.
To maintain the sprocket on the camshaft dowels, stop disks are mounted at the fore and aft of the sprocket. These stop disks are fully mounted on the camshaft dowels and rotate with the camshaft. During camshaft timing adjustment the stop disk faces slide along the sprocket faces.

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.

The splined shaft axial movements caused by the camshaft lashes are facilitated by the helical gear wear, but they are also enhanced by sprocket rotational play.
The sprocket is mounted rotationally by the splined shaft and timing chain. The splined shaft and sprocket helical gears wear and create play as noted above. Also the timing chain has excess length. The helical gear play and timing chain excess length combine to create sprocket rotational play.
When the camshaft lash moves the splined shaft axially the splined shaft also engages the sprocket. Due to the sprocket rotational play the splined shaft axial movement causes to rotate the sprocket. This allows the splined shaft to have longer axial movements. These longer movements enhance the effect of the camshaft lashes on the splined shaft. The splined shaft axial movements become stronger and more able to engage associate components play and cause it to rattle.

Diaphragm spring rattle solution

In an attempt to reduce the rattle BMW introduced a diaphragm spring that improves the sprocket mount and dampens its rotational play.
The diaphragm spring is included as part of the camshaft sprocket apparatus. In addition to the sprocket outer stop disk, a diaphragm spring (concave plate) followed by an additional stop disk are installed. When the last outer stop disk is mounted on the camshaft dowels the diaphragm spring is compressed. This causes to press the stop disks on the fore and aft of the sprocket onto the sprocket faces. This creates resistance to sprocket rotation and dampens sprocket rotational play movements. This acts to inhibit splined shaft axial movements and in turn reduces the rattle.
The diaphragm spring force is not excessive and thus still allows the sliding of the stop disk faces along the sprocket faces during camshaft timing adjustment.

Diaphragm spring retrofit

Pre March 95 build E36 320i/325i/Euro 328i and E34 520i/525i cars can retrofit install the diaphragm spring. To do this the existing camshaft dowels are replaced with longer dowels and the sprocket outer stop disk is replaced with a stop disk, diaphragm spring, and stop disk.
The needed parts are available from BMW and are listed in this repair procedure.

Symptoms

Vanos rattle at a certain RPM range, often 1800-2200 RPM. Rattle can also occur at idle.

Repair Procedure

 

The following is a single vanos intake sprocket diaphragm spring retrofit repair procedure.
The procedure applies to pre March 95 build E36 320i/325i/Euro 328i and E34 520i/525i cars.

This repair should be performed with the single vanos seals repair and single vanos rattle repair.

Single Vanos Seals Procedure, Single Vanos Rattle Procedure

Repair time: .5 hours mechanic, 1+ hours DIY.

Parts, Tools, and Shop Supplies

Parts with part number pattern xx-xx-x-xxx-xxx are BMW parts and can be acquired from a BMW dealership.
Vanos-BMW.com does not provide any of the following parts.

First intake sprocket outer stop disk (thin) (11-36-1-403-822) $49.67/each, intake sprocket diaphragm spring (11-36-1-403-550) 7.67/each, second intake sprocket outer stop disk (thick) (11-36-1-403-823) $19.45/each, 3 x intake sprocket studs (11-36-1-403-824) $6.39/each, 3 x intake sprocket nuts (07-11-9-900-910) $.25/each

Note: Do not utilize nut referenced in BMW Service Information. Nut referenced supersedes to nut that does not work. Nut over tightens sprocket diaphragm spring and prevents ability to perform timing rotation adjustment. Nut listed above is from BMW ETK and works properly.

10mm socket 3/8”, 10mm deep socket 3/8”
3/8” ratchet, 3/8” socket extension (short)
3/8” torque wrench (10 Nm [7 ft-lb], 22 Nm [16 ft-lb])

Magic marker

Not shown: small cloth towel

Repair

Repair is performed once vanos is removed from engine. Refer to single vanos repair procedure, Single Vanos Procedure

Intake camshaft must be locked per method specified in single vanos repair procedure.

Removal of sprocket components

Insert cloth towel below intake sprocket. This will prevent any falling bolt/nut from dropping into oil sump.

Remove intake sprocket 3 mounting nuts (10mm socket 3/8” / 3/8” ratchet & extension).

Remove intake sprocket outer stop disk.

Mark intake sprocket and chain matting at top (marker).

Mark exhaust sprocket and chain matting at top (marker).

Remove intake and exhaust sprockets and chain as one part.
Do not disconnect chain from sprockets. Keep sprockets separated to maintain chain mount.

Note: Outer disk at exhaust sprocket is missing in picture.

Lay down sprockets and chain on table. Keep sprockets separated to maintain chain mount.

Intake and exhaust after sprockets removal.

Remove intake sprocket 3 mounting studs (10mm deep socket 3/8” / 3/8” ratchet).

Note: Maintain intake inner stop disk and notched wheel on camshaft.

Installation of sprocket components

Install intake sprocket 3 new mounting studs (10mm deep socket 3/8” / 3/8” ratchet).
Fully tighten 22 Nm (16 ft-lb) (10mm deep socket 3/8” / 3/8” torque wrench).
Note: Tighten studs evenly in multiple passes.
Note: Verify one pass with all studs fully tightened.

Note: Old inner stop disk was removed and cleaned. This is not necessary.

Install intake and exhaust sprockets and chain onto camshafts.
Keep sprockets separated to maintain chain mount.
Note: Rotational position of sprockets is not important. This will be set when vanos is installed.

Install intake sprocket new first outer stop disk onto intake studs (thin plate, 2mm).

Install intake sprocket new diaphragm spring onto intake studs.

Install intake sprocket new second outer stop disk onto intake studs (thick plate, 4mm).

Install intake sprocket new 3 mounting nuts (10mm socket 3/8” / 3/8” ratchet & extension).
Fully tighten 10 Nm (7 ft-lb) (10mm socket 3/8” / 3/8” torque wrench & extension).
Note: Tighten nuts evenly in multiple passes.
Note: Verify one pass with all nuts fully tightened.

Remove cloth towel from below intake sprocket.