535i intake manifold gasket replacement write-up

I recently replaced the intake manifold gaskets on my 535i M30. One of the gaskets had failed so there was an air leak and I was getting the 1222 oxygen sensor code. A good independent shop gave me a price estimate of $500-700 for the job. The task of removing the intake manifold was not as hard as I had been led to believe -- people had mentioned how difficult it is to reach some of the 12 nuts holding it on, but with the right tool it was easy. Taking my time, disassembly and reassembly of everything took about 4 hours each for me, a moderately experienced home mechanic.

The key trick was to use a universal-joint 12mm socket on the hard-to-reach nuts that people mention. The problem with these nuts is that their axial centerline points slightly upwards towards the underside of the manifold, so socket and extensions have to angle away before they hit the underside. The universal joint permits that angling away. In a couple of cases (nuts 5, 6), it was hard to get the socket off after tightening the nut, because the clearance was so small!

To reach these nuts, put the universal socket on the end of several straight extensions, and guide it high along the underside of the manifold (above the coolant hoses), straight towards the relevant stud. Slide the other hand underneath the manifold and put a thumb and finger on either side of stud to guide the socket on, slipping it on so it feels like it points up slightly. Unless you have even longer arms than me (I'm 6'1"), you can indeed reach each of the studs with the guide hand. All the nuts could be loosened/tightened with the extension bars coming pretty much straight out. No need to go underneath the car. Don't lose the wave washers under the nuts, a magnet can help to bring them out.

I did not use the S and half-moon wrenches I had ordered, the universal socket did all lower nuts, with the added advantage that a torque wrench could be used to tighten the nuts. Reaching some of the top row of nuts was helped by disconnecting the wiring tray from injectors. The hard-to-find part number if any of the little black clips (that go over the injector connectors, and along the bottom of the wiring tray) break is 12 51 1 711 433.

You do not need to take off the two coolant hoses running under the manifold (just remove them carefully from the plastic clips), nor the oil filter housing or fuel rail. For access, I did remove the manifold support bracket, and disconnected the gasoline vapor valve/hoses. To take the manifold all the way off, which possibly is not necessary, you also have to disconnect the fuel lines somewhere (I did at manifold support bracket), the brake booster vacuum tube, throttle and cruise control cables and cable bracket, injector connectors, throttle position sensor connector, and charcoal canister gas line.

Hope that's useful,
Marcus

'92 535iM Lazurblau

Good write up. I will keep that in mind if I have to do it myself one day. Is the socket you used a 12mm socket that you connected into a universal piece or was it all one part? Did that solve your vacuum leak?

Myles

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Originally Posted by myles

Good write up. I will keep that in mind if I have to do it myself one day. Is the socket you used a 12mm socket that you connected into a universal piece or was it all one part? Did that solve your vacuum leak?

Myles

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The socket was all one part, available from either Sears Craftsman or Snap-On, I can't remember which. I wanted to get it all one piece since that was most likely smaller than a two-piece combo, and better able to fit in the tiny clearances.

The vacuum leak was indeed solved. The engine never ran poorly, but after a while the leak got so big that you could actually hear a whistling in the engine bay.

Mine's been leaking for a long time now. I have the gaskets, does the coolant resevoir need to be removed?

Having just replaced the head gasket in my 535, I have perspective on this as well.

I removed the intake manifold from the head before removing the head from the car. It sounds like you never had to deal with the joys of removing the injector clips from the injectors since you didn't remove the manifold from the car. That turned the 2 minute job of removing the wiring box from the manifold into a 2 hour job of screwing around with a scribe and tiny needle nose pliers to get the clips off before I could remove the wiring box.

Not sure what the deal was with your hose clips, but mine were quite reluctant to unclip from the hoses. The mounting tab was broken off one of them, so I replaced both. I replaced them before reinstalling the manifold, but I think that they would have been a significant pain to replace with the manifold installed.

One thing you did that I didn't do--and in hindsight definitely should have done--is remove the support bracket from the bottom of the manifold. That definitely put a crimp in my style.

I tried both 3/8" drive and 1/4" drive 12mm flexible (U-joint) sockets. I wasn't able to get the 3/8 socket on most of the nuts because there wasn't enough clearance machined around the mounting ear on the manifold. My socket is Craftsman, so maybe the Snap-On is profiled a little differently and will work. Since I don't have a 1/4 drive torque wrench, I wasn't able to torque the lower ones.

I was able to use the aforementioned small needle nose pliers to place the washers from above, reaching between the runners. I was also able to start the nuts this way using my fingers, so I only had to tighten them from underneath.

The ABS and wiring on the strut tower made it difficult to get my elbows far enough into the engine bay to reach under the manifold.