BMW E31 840i, E32 AND EARLY E38

The M60 V8 engine used in the E31 840i, E32 and early E38 730i and 740i's seem to suffer from PCV valve failure when they reach a certain age. The PCV valve is kind of bellows that is fitted to the rear of the inlet manifold and when this is damaged it can cause erratic idling and excess smoke. Often mistaken for Nikasil problems the repair is pretty straight-forward but does require a bit of patience especially when trying to get the Torx bolts out of the bellows assembly.

Start the repair by removing the plastic engine covers, the fixings are found underneath the small covers and are all 10mm nuts. Start with the top cover and then remove the side covers.


Remove the soundproofing from the top of the manifold....


Remove microfilter cover

Remove microfilters

Remove cowling

Access to the nut that holds the coolant tank is obstructed by the diagnostic connector so remove the cover along with the security strap, loosen the big plastic nut and drop the connector down enough to get to the nut (10mm plastic self tapper). (Only E32)

Disconnect the pipe that connects to the right top of the expansion tank (push fit), undo both plastic nuts and move the tank off to the left hand side of the engine bay (no need to drain the coolant). (Only E32)

Disconnect the large loom that goes to the right hand wiring bank above the injectors and unclip the loom from this mounting just above the bellows. Remove the squashy-rubber insulator from behind the bellows housing, it's a bit fiddly but it comes out quite easily without tearing it.

 The picture also shows the vacuum pipe that runs from the fuel-pressure regulator to the bellows housing, this is the new pipe, the old one was damaged, squashed and had a hole in it....

The picture below shows the manifold and PCV valve at the rear. You can see the Torx bolts (6) than need to be removed. This is the most tricky part as there is little access to the bolts:

Next, remove the Torx-headed bolts from the bellows housing, access is quite tight, the lower bolts are close to the engine housing so use the bit in different-length extensions for each bolt.

The lower-left bolt could only be undone using a pair of mole-grips holding the Torx bit (don't try a spanner, the bit drops out and you won't find it again).....

The picture shows the clip that holds the breather pipe to the bellows housing, lever this upwards using a short screwdriver while holding on to it, you won't want to lose this between the cylinder heads.... The picture also shows an additional pipe that is fitted to the new bellows housing, this needs blocking off on the 730i's but is used on the 740i's for the brake system, I used a blind grommet which fitted snugly which was then covered in heatshrink and shrunk in position for security...

EDIT: Quite a few people have had problems getting the Torx screws out from the bellows housing. The most important point is to use a quality Torx bit. It must fit tightly in the head of the bolt, if it wiggles around you have very little chance of getting a good enough purchase on the bolt. Only put pressure on the bit when it is properly seated, too little pressure and the Torx will round off.

If you are in a situation where you just cannot get the Torx bolt out (if, for instance, the Torx head is damaged) then there are a number of possibilities. Most successful so far seems to be to melt the bellows using an old soldering iron so that access can be made to the errant Torx bolt (this is usually the one at the bottom at the passenger side). Melt enough away so that you can get a drill in there........drill a hole across the bolt and fit a self-tapper in the hole. Then use a pair of Mole-grips to turn the head of the bolt.

I have heard of people whacking the bellows into submission but be warned that the manifold is made of the same material and may well give up at the same time. The Torx bolts are sleeved which means that even after you have completely demolished the bellows you will still be left with a Torx bolt in a sleeve.

I'm always happy to hear of your own method of getting these bolts best tip is: Buy a brand new high quality Torx bit....for a fiver you are at an advantage to start with.....

This last picture shows (but only just) where the other end of the aluminium pipe joins to. This is right at the front of the engine near the throttle-return spring looking from the left-hand side of the engine bay. Right in the centre of the picture and framed by the smaller of the looms is the crankcase breather outlet. Make sure that the aluminium pipe is reasonably tight on this outlet and that the 'O' ring is fitted to the inside bore of the aluminium tube, the tube can slide backwards and forwards on this outlet to enable the bellows housing to be lifted straight upwards....don't let it drop off like I did!......

Reassembly is just a reversal of the process as they a new gasket to the bellows housing and stick a bit of silicone grease around it for good measure.

 Lose the rest of your knuckles doing back up the Torx bolts on the bellows housing....or, use Hex bolts instead as shown here:

do them up loosely to start with, the housing needs jiggling around to get each bolt in. Line up the aluminium tube on the bellows housing and use a screwdriver to push the tube from the front end of the car towards the housing (not forgetting to grease the 'O' ring on each end first). It is also easier (unless you are left-handed) to get a helper to push the tube from the front while you guide the tube over the bellows housing 'O' ring as it is quite a snug fit. Everything else is straight forward but just remember a couple of things: The coolant expansion tank loom goes behind the tank and up through the middle between the bulkhead and the centre of the tank. The coolant tank nuts are made of plastic and are self-tapping, don't do them up too tight. Be careful with the insulation behind the bellows housing to ensure this does not squash the vacuum pipe that runs between the fuel pressure regulator and the bellows housing. That's it all done...time for a cup of tea......Tim....

Big thanks to GarethF for the additional E31 pictures