6-cylinder Single Vanos Diaphragm Spring Procedure

The following information about the 6-cylinder Single Vanos is provided for reference purposes only. Use it at your own risk
In no event shall Beisan Systems, LLC or its members be liable for minor, significant, or special loss or damages of any kind however caused.

Introduction

BMW introduced its first variable valve timing systems in 1993. They named their variable valve timing unit ‘Vanos.’ BMW initially introduced the single Vanos (intake adjustment) on the standard i6 engine in the E36 320i/325i and E34 520i/525i car models.

Introduction to BMW’s Vanos System

The Rattle Issue and Diaphragm Spring Solution

BMW soon noticed that their variable valve timing system tended to rattle. To fix this, they added a muscle sheet spring to the intake gear on the camshaft. This spring helps reduce sprocket movement, which lowers the rattle. BMW later included this design in all standard i6 single Vanos models, except for the Euro 328i. In March 1995, they introduced it to the E36 320i/325i/Euro 328i and E34 520i/525i.

Owners of E36 320i/325i/Euro 328i and E34 520i/525i models built before March 1995 can install this diaphragm spring to reduce the rattle.

Technical Background

To understand how the diaphragm spring reduces the rattle, it’s important to know how BMW’s variable valve timing works.

How Variable Valve Timing Works

Variable valve timing adjusts when engine valves open and close. BMW’s system changes the timing without changing the camshaft’s shape. Instead, it shifts the timing of valve movements in relation to the engine shaft. Turning the camshaft clockwise makes the valves open and close sooner, while turning it left turn delays their timing.

This system uses helical gears, which need to rotate to engage. This turning allows the camshaft’s position to change while the engine is running.

Camshaft and Sprocket Connection

The camshaft and sprocket are not directly attached. Instead, the sprocket has a hole larger than the camshaft end, and both parts connect using helical gears. A splined shaft with gears on both its inner and outer walls links them together. The inner gears connect to the camshaft, while the outer gears connect to the sprocket.

Adjusting Valve Timing

Moving the splined shaft in or out adjusts the camshaft’s timing. Since the timing chain holds the sprocket in place and the helical gears prevent the splined shaft from turning, the camshaft rotates when the splined shaft moves.

Pushing the splined shaft in makes the camshaft rotate clockwise, advancing valve timing.
Pulling it out makes the camshaft rotate counterclockwise, delaying valve timing.

The Role of the Vanos System

The Vanos system, a fluid-powered mover, controls the splined shaft’s movement. Specifically, it has a piston with oil chambers at the front and back. By adjusting the oil pressure in these chambers, the system then moves the piston.

The piston has seals that keep oil inside while allowing smooth movement. The splined shaft connects to the piston and moves along with it. A bearing at the piston’s center lets the splined shaft spin with the camshaft and sprocket without affecting the piston itself.

In engines without variable valve timing, the camshaft sprocket is directly attached to the camshaft. However, in BMW’s variable valve timing system, the sprocket connects to the camshaft via a splined shaft. While this connection allows for independent rotation, it doesn’t fully support the sprocket on its own. To address this, BMW developed a system that keeps the sprocket securely in place while still enabling it to rotate independently for timing adjustments.

The camshaft has three dowels that stick out, and the sprocket has three matching slots. These slots fit onto the dowels, allowing the camshaft to slide within them during timing adjustments. This design lets the camshaft rotate independently of the sprocket.

To keep the sprocket in place, stop disks are installed at the front and rear. These disks are securely mounted to the camshaft dowels and rotate along with the camshaft. During timing adjustments, the stop disks slide against the sprocket’s surface, ensuring smooth movement and stability.

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 engine shaft, but also reciprocally the turning of the engine shaftcauses the axial positioning of the splined shaft.
Over time and with continued use, the helical gears on the camshaft, sprocket, and splined shaft develop wear along their gear spline side contact surfaces. As a result , this wear creates excessive play between the helical gears. Consequently , it leads to excessive play in how the splined shaft fits with the camshaft and sprocket. This issue manifests as axial play between the splined shaft, camshaft, and sprocket.

Diaphragm Spring Rattle Solution
To reduce the rattling noise, BMW added a muscle sheet spring. This part not only strengthens the sprocket mount but also reduces its turning movement.

The camshaft sprocket setup includes a muscle sheet spring. Along with the outer stop disk, the assembly also has a diaphragm spring (a curved plate) and an extra stop disk. When you tighten the final outer stop disk onto the camshaft dowels, it compresses the muscle sheet spring.

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 muscle sheet 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 achieve this, replace the existing camshaft dowels with longer ones and swap the sprocket’s outer stop disk with a new assembly consisting of a stop disk, diaphragm spring, and another stop disk. BMW supplies the necessary parts, which 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.
Beisan Systems 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

Important: Do not use the nut mentioned in the BMW Service Information. Instead, use the nut referenced above, which comes from the BMW ETK. This new nut replaces an older one that does not work properly. The old nut over-tightens the sprocket diaphragm spring, making it impossible to adjust the timing turning correctly. The nut listed above functions as intended and avoids this issue

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 Seals Procedure

Intake engine shaft 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 the three 10mm mounting nuts from the intake sprocket using a 3/8″ socket, ratchet, and 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 the intake and exhaust sprockets along with the chain as a single unit.
Do not separate the chain from the sprockets. Keep the sprockets apart to maintain the chain’s position.

Note: The outer disk on the exhaust sprocket is missing in the 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 engine shaft.

Installation of sprocket components

Start by installing the three new mounting studs onto the intake sprocket using a 10mm deep socket (3/8″ socket with a 3/8″ ratchet). Next , fully tighten the studs to 22 Nm (16 ft-lb) using a 10mm deep socket (3/8″ socket with a 3/8″ torque wrench). First , ensure that you tighten the studs evenly in multiple passes to avoid uneven pressure.
Afterward , verify that one pass includes all studs being fully tightened.

Finally , remove and clean the old inner stop disk.

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.

Begin by installing the new first outer stop disk (thin plate, 2mm) onto the intake studs of the intake sprocket.

Next , add the new diaphragm spring onto the intake studs.

Then , install the new second outer stop disk (thick plate, 4mm) onto the intake studs.

Finally , secure the intake sprocket by installing the three new mounting nuts using a 10mm socket (3/8″ socket with a 3/8″ ratchet and extension).
First, fully tighten the nuts to 10 Nm (7 ft-lb) using a 10mm socket (3/8″ socket with a 3/8″ torque wrench and extension). Next , ensure that you tighten the nuts evenly in multiple passes. Additionally , verify that one final pass is completed with all nuts fully tightened. Finally , remove the cloth towel from below the intake sprocket.