Changer son Vanos

[Paul]

Ce document propose une méthode pour enlever l'unité de commande Vanos (simple) et les arbres à cames sur un moteur S50. Le but de cette manoeuvre étant de remplacer certains composants : le pignon de came, le tendeur supérieur de chaine et les poussoirs hydrauliques sur un moteur totalisant un peu plus de 200.000 kilomètres.

Matériel nécessaire	Outils suggérés
Bentley Service Manual Douilles et clés métriques (8 mm-22mm) clé combo de 36mm Douille Trox E10 Plusieurs tournevis Stiff wire (coathanger wire)	Appareil photo/caméra Crayon et calepin pour les croquis Chiffons (beaucoup)
Matériel spécial	Eléments remplacés
Camshaft Locking Tool Flywheel Locking Pin	Upper Chain Tensioner Intake Sprocket Poussoirs hydrauliques

1 - Pré-requis

I broke this procedure into two working sessions driven primarily by the requirement that the engine be completely cold before removing the camshafts and bearing journals to prevent them from warping or distorting as different metals cool and contract at different rates.

After parking the car in the operating theater where it would remain for the duration, I allowed the engine to cool enough to remove :

- The mechanically driven cooling fan and shroud,

- The plastic engine covers,

- The ignition coils (spark plugs were loosened to relieve compression resistance, but left in their bores) and ignition wiring harnesses and

- The valve cover, gaskets and intake camshaft oil splash guard

Having most of the tedious work out of the way, I was able to begin the more mysterious part of the task early the next morning.

2 - Fixation du moteur

The first step is to get the engine oriented with cyl. 1 at TDC, as marked on the harmonic balancer on the front of the engine. Consult Bentley for the location of the timing marks and casing refrence point. This was achieved by using a 22mm wrench on the harmonic balancer bolt to rotate the engine clockwise until BOTH Intake and Exhaust camshaft lobes for cyl. 1 were pointing towards each other (see video above) AND the timing marks indicate TDC. This is where you will appreciate having loosened the spark plugs to relieve engine compression. You will encounter much more resistance while turning the engine and the compressed air may cause the crankshaft to rotate slightly.

At this point, the timing relationship of the valvetrain and engine were secured using the flywheel locking pin as indicated in the transmission housing located below the intake manifold and by securing the camshafts with the locking tool at the rear of the engine. The tool has two channels which mate with the squared ends of the camshafts to lock them in position.

Camshaft locking tool securing intake camshaft at rear of engine

With these components secured, I used the retaining pin included with the replacement Upper Chain Tensioner to compress and lock the existing tensioner in place.

Top view of pin securing guide rail of Upper Chain Tensioner

Next, I removed the two access plugs on the VANOs control unit that sit directly in front of the exhaust camshaft sprocket, allowing me to use the E10 Torx socket to loosen, but not remove, the four Torx bolts securing the secondary timing chain sprocket to the primary chain sprocket and exhaust camshaft.

Fuzzy picture of Exhaust Sprocket Torx bolt access plug location

3 - Déconnexion de l'unité de contrôle du Vanos

I now turned my attention to disconnecting the ground connection and oil supply line to the VANOs control unit. Pointing towards the firewall on the driver's side of the unit is the solenoid used to direct pressurized oil to either the front or rear of the control unit plunger. Rather than attempting to locate the wiring plug for the solenoid (it's a tight fit under the intake manifold and I couldn't see the plug) I chose to use the 36mm wrench to unscrew it from the body of the VANOs unit. There was ample wire for the half dozen or so turns required, but due caution and pampering is always a given.

Solenoid and oil line banjo fitting removed from VANOs control unit

Next, I removed the bolt attaching the oil line banjo fitting to the control unit after padding the area with rags to catch oil from the line and control unit itself. Remember, the big housing is full of oil and you'll wind up pumping nearly all of it out in the process of removal.

This left the ground connection and what I'm assuming is an engine hoist bracket to be removed. There are two bolts holding the bracket and I wound up removing the top (where the wire is connected) and loosening the lower bolt that goes into the thermostat housing. This allowed me to rotate the bracket out of the way and not misplace it.

Bracket in place around VANOs and...

Bracket rotated CW out of the way

The 10mm nuts securing the control unit may now be removed, but two bolts are serving another use by holding a small plastic wire shroud in place with the aid of two circlips (or e-clips). These must be removed and a deep 10mm socket used to remove the remaining two bolts.

Circlips holding wire shroud	Circlips and shroud removed
10mm Deep Socket being used to remove two remaining nuts	.

Having loosened all other components, I used the 36mm wrench again to remove the primary chain tensioner on the passenger side of the engine. Bentley calls for another special tool (part #) to replace the tensioner for the procedure, but I did not have it and thus did not use it.

4 - Retirer le Vanos

I didn't have the special tool (part#) to rotate the exhaust sprocket while removing the VANOs, and was uncertain exactly what chain of events would be needed to liberate the control unit aside from Bentley's instructions to "rotate exhaust sprocket while removing. . ." Different approaches to rotating the sprocket and secondary chain yielded no results and nearly convinced me to reverse all operations up to this point.

The Secret: When I was pulling the control unit away from the engine, the splined cup that mates the intake sprocket to the splined insert on the camshaft (see pic# XXX below) remained in place while the shaft extended out of the control body revealing three nuts holding the washers and thrust plate against the intake sprocket. At this point, the plunger of the control unit was fully extended about an inch out of the body.

Detail of three nuts securing thrust plate and intake sprocket to camshaft. Note the helical splines inside the intake sprocket and outside the camshaft insert. The VANOs splined cup meshes into that void. Se pic #XXX for a detail of the splined cup.

I used an 8mm (?) wrench to loosen the nuts, leaving both intake and exhaust sprockets loose, but still holding everything in position.

At this point, I highly recommend visually documenting the relationship of all the parts involved, noting markings on the sprockets, the position of chain links to those marks and to static points on the cylinder head. In addition to the video record I took, I also made notes and sketched crucial points of alignment as a potential remedy to Things Going Bad. I respect the precision and tollerances involved in timing the valvetrain components, and any assistance in insuring that I don't muck them up is always worth the time.

The moment of truth involved pulling the control unit slowly off of the engine which drew the splined cup out of it's nesting place between sprocket and shaft. This caused the entire secondary timing chain to rotate clockwise about 6deg. Releasing pressure on the thrust plate allowed the intake sprocket to rotate, and the opposing helical splines being drawn out did the rotating. At this point, I did another thorough documentation of relations and orientations. The VANOs was in my hands.

Sprockets without VANOs and. . .

VANOs control unit. Note splined cup

I finished the removal of the nuts holding the two washers, thrust plate and intake sprocket, removed the four Torx bolts and pulled the upper timing chain and sprockets off together. The upper chain tensioner can now be removed with three bolts on top and one on the front. I released tension on the guide and transfered the retaining pin back to the new tensioner to be installed later.

Secondary chain and sprocket removed exposing primary timing chain and exhaust sprocket

Finally, I made careful note of markings on the primary chain and exhaust sprocket and removed the sprocket. With a bit of wiggling, it came off the camshaft and out of the chain. I made sure to keep tension on the chain at all times to prevent it from slipping teeth on the drive sprocket, but more importantly so I wouldn't drop it into the engine. I've learned to use shop rags and foam to cover or block as many recesses and holes as possible when working on an engine as the smallest parts tend to seek out the most obscure and dangerous voids.

I used a length of coathanger wire to secure the chain to the large coolant hose just below the cylinder head. Enough tension to hold it securely, but no more.

Primary exhaust sprocket removed

Primary chain wired to coolant hose

5 - Removing the Camshafts, Journals and Lifters

The last remaining task of removing the camshafts themselves is fairly straight forward, but deserves all due caution.

Due Caution : The method of camshaft removal I used of evenly loosening the bolts across all the bearing caps in a pattern is SPECIFICALLY DENOUNCED by Bentley, but I was reassured by very reputable Others that this method, WHEN DONE PROPERLY posed no dangers or risks to the integrity of the components.

I have preformed this operation numerous times on my ZX-9 engine to adjust solid lifters and felt comfortable with the procedure. If you have not preformed this operation before or are not comfortable with the thought of camshafts and bearing caps wanting to spring out at you, I highly recommend the advice or assistance of someone who has, or that you find another, less critical motor to practice on until you are comfortable and confident.

Specifically, the process is to begin loosening the nuts holding the bearing caps in a regular pattern about 1/4 turn at a time. Cam lobes push the lifters and valves down and valve springs push the valves and lifters back up. at any given time, some of the lobes are pointing down and compressing the valve springs. It is this return pressure that must be overcome in a slow, controlled manner.

It is also crucial to release the bearings and camshaft as evenly as possible as a twisting force on the camshafts can dent, mar or distort the softer aluminum of the bearings.

Once the camshaft is removed, the lower bearing webbing which also serves to hold the hydraulic lifters in place can be removed by lifting straight up off the bolts that held the bearing caps. At this point nearly every hydraulic lifter will fall out and onto the springs and retainers protruding from the cylinder head.

Bearing journal and lifters in their bores, upside down

Closeup of bearing surface and lifter bores. Top view.

That's it. At this point, I replaced the old lifters with the new, inserting them into the bottom of the bearing frame. The hardest part was to get the lifters to stay in their bores without falling out while the entire unit is lowered into position over the bolts and valves. After one unsuccessful attempt, I created a long ribbon of masking tape by folding a length over upon itself, sticky sides together which gave me a long band I could wrap under the length of the frame, around the ends and over the top, providing a strap to prevent the lifters from falling out while I positioned the frame on the bolts. Once the entire piece was in place and lowered onto the valves and reatainers, I slid the ribbon out the end, allowing the lifters and frame to drop into their final position.

6 - Installing, or undoing what you just did.

To quote Bentley, Installation is the reverse of removal. It is advisable to enlist the services of a friend to help you initally push the camshafts into position while you replace the bearing caps as the valve springs will resist this, making the task cumbersome for one person. I was able to do it alone, but at 6'7" and 230lbs, I had a (barely) sufficient mechanical advantage.

Once I had the valvetrain reassembled, the VANOs unit replaced and the primary chain tensioner installed, I rotated the engine several times with the bolt on the harmonic balancer to make sure that I hadn't disrupted the timing and placed a valve where a piston wanted to be or vise versa.

I reassembled the remainder of the engine, put the key in the ignition and puckered whatever would pucker until I heard the strong, smooth idle of an inline six that I've grown to love.

7 - Epilogue

My primary goal was to reduce a loud and continuous lifter ticking I've had for a while and to attempt to get rid of the 'marbles-in-a-can' noise right next to the VANOs unit on the front of the engine.

I'm happy to say that the marbles noise is completely gone, and I now only occassionally get ticking from the lifters. Of major import is the return of strong, crisp power and throttle response from the engine which I attribute to loss of lift with the older, worn lifters. I wonder now if the bearing journals would bear replacing as well, since their aluminum bores hold the steel lifters and serve to channel the pressurized oil used to pump them up. Even though they looked perfectly fine and fit snugly, I'm curious if slight wear of the bores would allow a significant leak of oil, enough to cause occasional ticking under certain conditions.

The final reward was the joy and satisfaction of completing what I had imagined to be a daunting task and becoming even more intimately acquainted with the heart of the beast. I hope others can experience this as well.

Many thanks to all who offered advice and wisdom. The BMW community is full of fantastic individuals.

Merci à Steve Klein pour cet article.