BMW Z3 M S50 Engine ‘Vanos Bolts’ preventative maintenance
Article submitted by Off Your Marks

So I took the M out today as the weather was fine. Warmed it up and went for a blast.

At a set of lights the idle was lumpy and pulling away it was stuttering. I pulled over and checked the engine and noticed the exhaust solenoid cover had a bit of paper gasket protruding. There was no oil loss so I limped home and removed the cover. All was dry so the seals had not failed but I took out the solenoids and replaced all 4 o rings and fitted a new gasket. Now spot on.

I noticed the bolts were easier than they should be to undo (should be torqued to 8Nm) As the solenoids are held fast against the plate, I think the play in the cover was preventing operation.

I just thought its worth everyone checking these bolts as it could have been a lot worse, especially is the seals had failed and pressurised the solenoid cover

Following on from my concerns I thought that I would do a bit of a pictorial write up to help others do a bit of preventative maintenance


OK, first up is a shot of the part that makes our S50 engine such an addictive thing own. The S50 Rolls Royce VANOS (variable Nockenwellensteuerung) variable camshaft timing device.

There are two packs of twin solenoids that operate on the exhaust and inlet side of the cylinder head. This write up deals with the LHS exhaust solenoids, but the same applies to the RHS, only difference is you need to remove the fan to get the whole cowling out

To get to these its best to create a little more room and remove the radiator fan cowling. the LHS is secured by a push rivet and then it lifts up and pulls out

Now, below the alloy vanos is a black plastic cover secured by 2off 10mm nuts – remove these and remove the cover to give access to the plugs for the Solenoids

Here is the plug

So, pinch the metal clip and pull out the plug

Once removed we can now remove the cover, first up make sure you put some paper towel or cloth down under the cover as some oil will come out when the Solenoids are removed. If you get oil coming out when you remove the cover then this indicated oil seal/O ring failure.

Now,you need to remove the valves. There are fitted rather snugly so you need to tease them out. I used a pair of soft jaw grips. Note the position of them and mark/photograph as needed.

Now, there are four wires on the SV’s, two on each and three on the plug – two wires are common

Use a contact cleaner to remove all the trace oil

Next is to check the coil resistance – This reading of 3.3 ohms is good. If there was no reading then this indicates a failed coil

A common failure is the soldered connections to fracture so I re-soldered them and bridge the solder to bypass the copper connection on the printed circuit board (copper link can fail too)

Its time to fit the replacement O rings on the valves now.

Once the O rings are changed, clean out the oil from the SV housing as there will be residue in there

Now pop the valves back in, taking care to fit them in the same place as before. The click home securely

Refit the cover along with new paper gasket and torque new bolts to around 8-10Nm

The refit is the reverse of removal, ie refit the plug connector and plastic guard.

Once you restart the engine, it will be a little lumpy for a few seconds whilst the oil pressure in the vanos builds up

Job Done

Hope that helps! Just do the same for the RHS now.