BMW Vanos Rebuild: S52 Engine Guide

The BMW M5x and S5x series engines are renowned for their performance and engineering prowess. However, a common point of concern for owners of these engines, particularly those featuring the single Vanos system, is the notorious 'Vanos rattle' and a general decline in performance over time. This often stems from worn seals within the Vanos (Variable Valve Timing) unit. Fortunately, this is a repairable issue, and with the right guidance and tools, you can effectively rebuild your Vanos unit, restoring smooth and consistent power delivery. This guide focuses on the single Vanos system found in the 6-cylinder M50TU, M52, and S50/S52 engines, providing a step-by-step process for installation of a rebuild kit.

Understanding Vanos Operation and Common Issues

BMW's Vanos system is an ingenious mechanism designed to optimise engine performance and efficiency by varying the timing of the camshafts. In single Vanos systems, this adjustment is applied to the intake camshaft. The system operates on hydraulic pressure, controlled by a solenoid, which actuates a piston within the Vanos unit. This piston, in turn, moves a transfer gear that is splined to the camshaft and its sprocket. The angled teeth on the transfer gear, when moved in or out by the piston, alter the relative position of the camshaft to its sprocket, thereby advancing or retarding the valve timing.

The most common failure point within the single Vanos unit is the set of seals that manage the hydraulic pressure. Over time and mileage, these seals degrade, leading to a loss of pressure and, consequently, incorrect or delayed valve timing. This can manifest as a loss of low-end torque, rough idling, and the characteristic 'Vanos rattle'. The rattle is often attributed to excessive axial play in the piston bearings within the Vanos unit. This play allows the components to move slightly, creating the audible noise.

Essential Tools for the Job

Before commencing the Vanos rebuild, it is crucial to have the correct tools readily available. Attempting this job with inadequate tools can lead to damage to critical components. The following tools are specifically recommended:

• Specialised Vanos Piston Cap Socket: Standard sockets often have a chamfered opening that can slip off the shallow hex on the Vanos piston cap, causing damage. You will need either a 17mm or 18mm socket, depending on your specific engine model. It is advisable to have both on hand.
• Water Pump and Fan Clutch Toolkit: This is invaluable for the initial disassembly stages.
• Camshaft Locking Tools: A set that allows you to lock both the crankshaft and camshafts in their timed positions is essential to maintain engine timing during Vanos removal and installation.
• Sprocket Turning Tool: This tool engages the exhaust camshaft sprocket and allows for precise rotation, which is extremely helpful during Vanos removal and reinstallation.

Step-by-Step Rebuild Process

1. Preliminary Component Removal

The process begins with gaining access to the Vanos unit. This involves removing several components from the top and front of the engine:

Items to remove:

• Air Box
• Air Duct, Radiator Fan, and Shroud
• Cabin Filter Housing (E39 models only)
• Engine Top Covers
• Valve Cover
• Ignition Coils

Once these are out of the way, you will have clear access to the camshafts and the Vanos unit itself, which is typically located at the front of the cylinder head.

2. Setting Engine Timing and Locking Components

Accurate timing is paramount. You must lock the engine's timing before proceeding with Vanos removal:

1. Place a socket and ratchet onto the crankshaft pulley centre bolt.
2. Rotate the engine clockwise until the lobes on cylinder #1's intake and exhaust camshafts are pointing towards each other.
3. Align the Top Dead Centre (TDC) mark on the crankshaft pulley with the corresponding mark on the front of the engine. A mirror and flashlight may be helpful for visibility.
4. Safely raise and support the vehicle. Locate the crankshaft locking pin hole on the driver's side rear of the engine block, just above the oil pan. Remove the plug and insert the locking pin. You may need to slightly rotate the crankshaft for the pin to fully engage with the flywheel or flexplate.
5. On the top side of the engine, remove the three valve cover studs from the rear of the cylinder head. Note the square cast into the end of each camshaft.
6. Slide the exhaust camshaft locking fixture onto the square end of the exhaust camshaft. Use an open-ended wrench on the camshaft hex to position it so the fixture sits flat against the cylinder head.
7. Repeat the process for the intake camshaft, ensuring its locking fixture also sits flat against the cylinder head.
8. Secure both camshaft locking fixtures together using the provided bolts and connecting piece.

3. Disconnecting and Removing the Vanos Unit

With the engine timed and locked, you can now disconnect and remove the Vanos unit:

1. Remove the banjo bolt securing the oil line to the Vanos unit and disconnect the Vanos solenoid connector.
2. Remove the engine lift bracket, which is typically held by two bolts.
3. Locate and remove the vacuum pipe that crosses the front of the Vanos unit (secured by two nuts). On some models, this may be a cable bracket. Disconnect any vacuum hoses and gently move the pipe out of the way.
4. Remove the two Vanos exhaust sprocket access caps.
5. Remove the four exhaust camshaft sprocket bolts. The lower two are accessed through the access cap holes.
6. Press down on the timing chain tensioner and insert a locking pin or suitable tool to hold it in its retracted position, relieving tension on the chain.
7. Remove the remaining Vanos mounting nuts. Some nuts may have already been removed depending on the specific engine model.
8. Engage the sprocket turning tool onto the exhaust camshaft sprocket. While holding the tool, simultaneously rotate the sprocket clockwise and pull the Vanos unit away from the cylinder head.

4. Vanos Unit Disassembly and Seal Replacement

Once the Vanos unit is removed, it's time to address the worn seals:

1. Place the Vanos unit on a clean workbench. Remove the five bolts securing the piston cover plate.
2. Carefully pull out the piston and cover plate from the Vanos housing. Thoroughly clean all components.
3. Inspect the cylinder walls of the Vanos housing. Minor marks from the piston seal are normal, but the walls should be smooth and free from deep scratches or pitting.
4. Using an Exacto knife or similar fine-tipped tool, carefully cut and remove the old Teflon sealing ring and the underlying O-ring from the piston groove. Extreme caution is advised to avoid scoring or scratching the piston groove.
5. Thoroughly clean the piston groove to remove any residue.
6. Install the new O-ring into the piston groove.
7. Prepare the new Teflon sealing ring by immersing it in warm water or holding it in your hands to make it more pliable. Start the ring on one side of the groove and guide it around. As it nears the end, you will feel tension build. Hold the seal in place and carefully pull it over the top of the piston to fully seat it in the groove.

5. Addressing the Vanos Rattle: ECS Bearing Ring Installation (Optional but Recommended)

To fix the common 'Vanos rattle', you'll need to address axial play in the piston bearings. This often involves installing a specific bearing ring:

• Understanding Axial Play: Axial play is the looseness or wobble in the piston bearings. While side-to-side (radial) play is normal, excessive axial play causes the rattle. The goal is to eliminate this axial clearance.
• ECS Bearing Ring: The ECS Tuning bearing ring is narrower than the original, allowing for a precise adjustment.
• Piston Disassembly for Bearing Adjustment:
• Secure the piston and cover plate in a vise using soft jaws or wood blocks to prevent damage.
• Using the special Vanos piston cap socket, loosen and remove the piston cap. Ensure you apply inward pressure on the socket to prevent slipping.
• Lift out the first end washer and roller bearing.
• Remove the transfer gear retaining bolt. Note that this is a left-hand thread, meaning it loosens in a clockwise direction.
• Remove the remaining components (transfer gear, second bearing, second washer). Clean all parts meticulously.
• If this is the initial installation of the ECS bearing ring, remove the original bearing ring and replace it with the new one.
• Adjustment Procedure:
• To Tighten (Eliminate Play/Add Preload): Place 400-grit sandpaper on a flat surface. Sand one side of the bearing ring, rotating it 90 degrees periodically, for about 30-40 passes. Repeat on all surfaces. This removes a tiny amount of material.
• To Loosen (If Too Tight): If the piston is too stiff after reassembly, you may need to slightly loosen the bearing race by sanding it in a similar fashion.
• Reassemble the piston components in the correct order, ensuring they are clean.
• Reinstall the piston cap and torque it to 40 Nm (30 Ft-lbs) using the special socket and maintaining inward pressure.
• Crucially, check for axial play/preload by feel. You want a smooth, even resistance with no noticeable wobble. You may need to repeat the adjustment procedure multiple times to achieve the correct tolerance (approximately 0.005-0.015mm).

6. Reassembling the Vanos Unit

With the seals replaced and bearings adjusted:

1. Coat the new Teflon sealing ring with clean engine oil.
2. Carefully insert the piston back into the Vanos housing at an angle, ensuring it slides in smoothly.
3. Align the bolt holes on the cover plate with those on the Vanos housing.
4. Install the five cover plate bolts and tighten them in an alternating pattern to 10 Nm (7 Ft-lbs).
5. Ensure the transfer gear remains fully pushed into the Vanos housing.

7. Reinstalling the Vanos Unit onto the Engine

This is a critical step requiring precision:

1. Ensure the old Vanos gasket is removed from the cylinder head and the sealing surface is clean. Install the dowel pins into the corner holes of the cylinder head.
2. Slide the new Vanos gasket onto the dowel pins.
3. Engage the sprocket turning tool onto the exhaust camshaft sprocket and rotate it clockwise as far as it will go. This will also rotate the intake sprocket.
4. With the transfer gear fully seated in the Vanos housing, slide the Vanos unit onto the cylinder head mounting studs.
5. The transfer gear has offset teeth. While pushing the Vanos unit inwards, rotate the transfer gear by hand to align its teeth with the intake camshaft sprocket. It is vital that the transfer gear remains pushed fully into the Vanos housing during this alignment.
6. Engage the sprocket turning tool on the exhaust camshaft sprocket. Rotate the sprocket slightly counter-clockwise while simultaneously pushing the Vanos unit inwards. As soon as the transfer gear teeth align, the unit will slide fully onto the cylinder head. Achieving the first possible tooth engagement is critical for correct timing. If unsure, remove the Vanos unit and repeat the alignment process.
7. Once the Vanos unit is seated against the cylinder head, install the mounting nuts and torque them to 8 Nm (6 Ft-lbs). Only install nuts that do not interfere with reassembly.
8. Remove the camshaft locking blocks.
9. Remove the crankshaft locking pin and reinstall the plug.
10. Install the four exhaust sprocket bolts and torque them to 20 Nm (15 Ft-lbs).
11. Reinstall the two Vanos exhaust sprocket access caps and torque them to 50 Nm (37 Ft-lbs).

8. Final Reassembly and Checks

The final stage involves reassembling all the components that were removed earlier:

• Reconnect the vacuum pipe and any associated cable brackets.
• Reconnect the Vanos oil line and solenoid connector.
• Reinstall the intake camshaft cover.
• Reinstall the valve cover, ignition coils, and engine top cover.
• Reinstall the cabin filter housing (if applicable).
• Reinstall the air duct, radiator fan, and shroud.
• Reinstall the air box.

It is also an opportune time to change the engine oil and filter.

Torque Specifications Summary

Here are some key torque specifications for this procedure:

• Piston Access Plugs: 50 Nm (37 Ft-lbs)
• Valve Cover Fasteners: 10 Nm (7 Ft-lbs)
• Vanos Intake Cover Plate Bolts: 10 Nm (7 Ft-lbs)
• Vanos Oil Line Banjo Fitting: 32 Nm (24 Ft-lbs)
• Vanos Unit Mounting Nuts and Bolt: 8 Nm (6 Ft-lbs)
• Exhaust Sprocket Bolts: 20 Nm (15 Ft-lbs)
• Vanos Exhaust Sprocket Access Caps: 50 Nm (37 Ft-lbs)

Frequently Asked Questions

What are the symptoms of a failing Vanos unit?

Common symptoms include a loss of low-end torque, rough idling, hesitation during acceleration, increased fuel consumption, and the characteristic 'Vanos rattle' noise, often heard at idle or just off idle.

Can I rebuild the Vanos unit myself?

Yes, with the correct tools, a good understanding of the procedure, and patience, you can successfully rebuild your Vanos unit. It is a moderately complex job but achievable for a competent DIY mechanic.

How long does a Vanos rebuild typically take?

If you are well-prepared with all the necessary tools and parts, the job can often be completed in a single afternoon. However, it's advisable to allocate a full day to avoid rushing and ensure accuracy.

What is the 'Vanos rattle'?

The Vanos rattle is a ticking or rattling sound commonly heard from the front of the engine on BMWs with single Vanos. It is typically caused by excessive axial play in the Vanos piston bearings, which can be rectified by replacing worn components and adjusting tolerances, often with the help of a specific bearing ring.

Do I need to replace the Vanos solenoid?

While this guide focuses on the mechanical Vanos unit, the solenoid is another common failure point. If you are experiencing Vanos-related issues and the mechanical rebuild doesn't fully resolve them, the solenoid may also need to be replaced.

Conclusion

Rebuilding the Vanos unit on your BMW S52 engine is a rewarding task that can significantly improve engine performance and eliminate annoying noises. By carefully following these steps and using the correct tools, you can restore your Vanos system to its former glory, ensuring smooth and efficient operation for miles to come.