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The engine: BMW’s S50 B32, fitted to the E36 M3 Evolution, and the Z3M roadster and coupe. A 3201cc inline six, in non-US specification with 6 throttle bodies, and 321 horsepower. A naturally inducted engine, with more than 100 horsepower per litre, and peak torque, all 258 lb/ft, available at only 3250rpm. Such a powerful yet flexible engine owed its broad spectrum of abilities to its variable lift and timing system, called VANOS.

This is the silver unit on the front of the engine, and uses oil pressure to operate continuously variable camshaft profiles on both the inlet and exhaust cams. It’s great, when it works.

The problem: The VANOS isn’t as tough as the rest of the engine. The exact problem is two-fold. One half of the problem, despite a good deal of research, still isn’t absolutely clear to me. I guess a combination of wear and tear, and perhaps design, causes the unit to rattle and growl as the engine falls from about 2000rpm to idle. I’ve heard that this can get so bad that the system stops working and requires a rebuild, but I’ve not actually known a system come to this.

However, the other half of the problem became very real indeed recently. Perhaps aggrevated by the cause of the rattling and growling, the bolts that hold one of the VANOS covers on can suffer from vibration fractures that lead to bolt failure. The most usual cover to fail is that over the exhaust side solenoid valves.

Having just started the car, while reversing, I was alerted to the thick trail of oil my car was leaving on the ground. I killed the engine, opened the bonnet, and was greeted by the image top right.

Two of the four bolts holding on the exhaust side solenoid valves cover had sheared. The cover holds the solenoids in place, and with 100 bar of oil pressure on the other side, once the cover was loose the solenoids gave way and the engine lost oil at an extremely high rate – at idle! In my case I was fortunate: I imagine that if this occurs while the engine is at high rpm, oil is lost so fast that only immediate shut off can prevent a seized engine.

Prevention and Repair: So long as the engine isn’t starved of oil, repair is possible for less than £25.

Prevention is of course quicker, cheaper and less messy than the cure, so I’ll cover that first. I’ll outline the parts I feel should be changed at service Inspections. Of course upon acquiring one of these engines or first reading this, I’d advise you perform the Inspection II changes immediately.

Inspection I: (~£2)
07.11.9.900.677 x4 (bolts)

Identify the four bolts that hold on the exhaust side solenoid cover, as shown in the image top right. Standing at the front of the car looking at the engine, it’s on the left; you may need to remove a piece of fan cowling to gain proper access.

Replace the bolts, one at a time, and use a torque wrench to tighten up to 8Nm. Do not have more than one bolt removed (or even loose) at any one time.

Inspection II: (~£10.00)
07.11.9.900.677 x8 (bolts)
11.36.1.401.973 x1 (filter screw)
07.11.9.963.073 x1 (sealing washer)

Identify the eight bolts that hold on the exhaust and inlet side solenoid covers, as shown in the image middle right. You’ll probably need to remove the fan (32mm spanner – inverse thread) and cowling to gain proper access.

Replace the bolts, one at a time, and use a torque wrench to tighten up to 8Nm. Do not have more than one bolt removed (or even loose) at any one time.

Then, remove the vanos filter screw, position shown in the image bottom right. Mop up any excess oil, and fit new screw and washer, tightening to 12Nm.

Maybe they weren’t torqued correctly, maybe these bolts can just fail after 23000 miles. Either way, for a few pounds, I hope you can see why I recommend renewing them so often.

The Cure is similar to my proposed Inspection II work, but with a bit of solenoid TLC too. Note! This procedure is my cure for damage to the exhaust solenoids and cover.

Parts (~£15)
07.11.9.900.677 x4 (bolts)
11.36.1.404.154 x1 (gasket)
11.36.1.318.788 x2 (‘o’ ring)
11.36.1.403.191 x2 (‘o’ ring)

Remove any remaining complete bolts, the cover, the gasket, and any parts of bolts left in the VANOS. This should expose the rear of the solenoids as shown in the top picture.

Using a cloth to protect the rear of the solenoids, and being extremely careful of their fragile wiring, use a pair of pliers to gradually work the solenoids free. Don’t be tempted to use any levers, and don’t expect quick progress, just twist the solenoids to and fro while gently applying force to withdraw them. Once they’re out, remove the two ‘o’ rings, one large and one small, from each solenoid. I used a knife to carefully cut them out. Clean all the oil from solenoids and the open front of the VANOS unit with a clean cloth.

Then, coat the four new ‘o’ rings in talcum powder, and fit them to the solenoids. Then refit the solenoids. If you’re unlucky enough to have damaged the solenoids and had to replace them (circa £210), you’ll get a solenoid alignment tool to help you align them. I didn’t, so just tried to put them back exactly as they came out. They should slide home with a rewarding ‘click’.

Finally, replace cover with new gasket and bolts, and tighten bolts to 8Nm. Top up engine oil level if necessary. When the engine is first started it’s likely to run rough for a few seconds while oil pressure builds and the VANOS sorts itself out.

I hope this article prevents people from suffering this nuisance, and helps to dispel some of the myths surrounding the VANOS issues with this engine.

Parts:
Filter Screw (BM11.36.1.401.973) @ £4.34 + V.A.T.
Vanos Filter Washer (BM07.11.9.963.073) @ £0.12 + V.A.T.

Tools:
Torque wrench set to 12Nm.
6mm hex drive.

(1) Remove the old screw, be ready to mop up a bit of oil.

(2) Prepare the new filter and washer.

(3) Do it up with a torque wrench. Simple!