[Mathew87]

Recently I found myself in need of replacing my N52 engine's valve cover gasket. After the car was sitting parked for a longer time, the winter cold-related contraction of the gasket was causing a serios leak directly above the exhaust manifold and cats. And each engine start-up was causing the oil to burn off those surfaces, filling the car with choking smoke. My N52 engine is the earliest type, with the incredibly light magnezium valve cover and 255 hp as standard.

There are many threads explaining all the details of the VCG replacement on this forum and all are very useful. Hovever, my experience doing it turned out to be a slow, one-month torture, because of BMW's stupidity of using the dreaded single-use aluminium bolts for the valve cover. My VCG had been replaced before by a highly rated, independent BMW repair shop, that had left the inner three bolts close to the spark plugs completely untightened, and the bolt on the corner, closest to both the firewall and the catalysts, snapped / broken by overtightening it.

And this presented a huge problem because:
1. The broken part of the bolt could not be drilled with any kind of drill (which can only be a hex drill) because of the need of using rachet extensions and a U-Joint. The tip of the drill was spinning randomly on the broken VC bolt because of the U-joint, unable to actually create a singular & centered digging point in it.
2. The broken bolt had actually become sort of welded (I am unsure how) to the cylinder head threads and no type of screw exctractor could turn it once I eventually managed to drill it completely. I ended up applying over 100 NM of force and I still could not move it. Not even a single milimeter. All while risking to break the cylinder head from too applying much force in its corner, a weaker part of the cylinder head.
3. Once completely drilled through, the broken bolt caused the threads in the cylinder head to become damaged / unusable and a new, standard M7 aluminium screw could no longer be used for that hole. Creating new, enlarged threads was also impossible because the space near the firewall and suspension tower did not allow the use of any thread repair tool, no matter how small it was.

Conclusions: "thank you" (or rather f**k you) BMW for your stupidity in designing thin bolts in M7 size made out of soft, easy to break aluminium. Cost-cutting at its finest in order to avoid the galvanic corrosion of the magnezium VC, at the point of contact between the bolt heads and the VC surface. The correct solution would have been the use of carbon steel bolts, plated with cadmium, that does not react with magnezium and is superior to zinc in its oxydation resistance, especially in salty environments such as salted roads or ocean / sea coasts.

After much trial and error, I identified solutions for BMW's design shortcommings:

A. For the VC bolts:

1. I eventually managed to drill a 3 mm pilot hole throght the broken aluminium bolt by using an increasing combination of diamond-tip burrs, attached to a right-angle Dremel 575 accesory, further attached to the Dremel 225-02 flex shaft, which connected to my Dremel 3000, set to very high speed (9 out of 10). Nothing else worked while the diamond burrs literally pulverize the softer aluminium. Thank you nature for creating this wonderful crystal. But unfortunately, a special washer fabrication is needed in order to connect the Dremel 575 to the Dremel 225-02, according to the instructions found in the following videos:

2. With a 3 mm pilot hole establised, I could use 4 mm, 5 mm and 6 mm hex drill bits attached to the U-joint and ratchet extensions, in order to enlarge the hole to accomodate a M6 screw.
3. Use of a stainless steel bolt, 60 mm long in M6 size, with a 15 mm M6 zinc-coated connecting nut threaded to it (in order to be used as a spacer), inserted from underneath the cylinder head, and connected from above with a stainless steel self-locking M6 hex nut.
4. Dremel precision-cutting all the old 19 M7 aluminium bolts with 5 mm thick aluminium washers, and 3 new M7 aluminium bolts with 5 mm thick aluminium washers (from a new set), in order to reuse those washers.
5. Enlarge the diameter of 21 out of the 22 aluminium washers to 7 mm by using a 7 mm cobalt drill (for the cleanest of metal cuts).
6. Using M7, 35 mm length, zinc-plated carbon steel hex bolts instead of M7 aluminium bolts, run through the 5 mm thick aluminium washers, in order to prevent galvanic corrosion between the carbon steel bolts and the magnezium valve cover, in the event that the zinc plating wears off over time. A 5 mm thick aluminium washer with unchanged inner diameter (around 6,5 mm) sits on the M6 stainless steel screw, between the valve cover and the M6 stainless steel self-locking hex nut.

B. For the magnezium valve cover:

1. Full sandblasting at a sandblasting shop, both inside and outside, along with its mating surface, in order to remove all the oxydation and corrosion occured over 18 years, in order to have a clean surface on whitch the new gasket will sit.
2. Full spray-painting in 2 coats, inside, outside, and on the mating surface, with stove paint (found one good for 600 degrees C), in order to prevent or at least slow down further oxydation and corrosion.
3. Coating the mating surface with a thin layer of gasket-maker red silicone, good for almost 300 degrees C, in order to fill all the tiny oxydation / corrosion holes of the mating surface that were exposed by the sandblasting.

For the valve cover gaskets (both inner and outer):

1. Coating their cylinder head mating surfaces with a thin thin layer of gasket-maker red silicone, good for almost 300 degrees C, in order to create a more durable seal and prevent a premature repeat of the gasket replacement job. The way in which it was originally designed, the gasket acts more like an additional galvanic corrosion protection between the valve cover and the cylinder head, than an actual gasket which should compress somewhat, in order to make a durable seal. Intead, BMW designed a thin sheet of metal, ripped in an extremely thin layer of rubber. Lazy design again.
2. Letting the silicone fully dry before installation on the cylinder head.

After full reassembly I can see that everything looks good. No leaks and the hex carbon steel bolts allowed me to tighten them much more than what the aluminium ones could have handled, in order to fully sqeeze the gasket maker silicone for a longer lasting seal. I am not at all concerned about their zinc coating which should provide good corrosion resistance for around 10 years, at which point they can be replaced with new ones. There is also plenty of clearance between the valve cover bolts and the valve cover holes as well (around one full milimiter), so no chance of galvanic corrosion there either. I will keep an eye on the way the hex head of the steel bolts looks over the comming years and will replace them at the earliest signs indicating that the zinc plating is begining to wear off.

An important note: I did this repair in Europe where I could find M7 zinc-plated carbon steel hex bolts in various lenghts. They are difficult to find in North America but McMaster-CARR has them. No M7 stainless steel bolts are produced in a standardized fashion anywhere in the world.

General valve cover removal and installation considerations:

1. Save your time, energy and mental sanity by first removing the entire cowl parts, including wipers and absolutely all the plastic pieces under them. The valve cover goes out and in like child's play in this way.
2. Without removing any of them, turn the injectors 90 degrees with their connector towards the firewall or the front of the car. This allows even more clearance for the valve cover to go out and in without breaking a sweat.

Some final thoughts: I think the plastic valve cover of later N52 engines is better because:

1. No chance of galvanic corrosion with using steel bolts of your choice.
2. It replaces the PCV valve from underneath the intake manifold which has a notoriously / impossibly difficult hose to attach (the one going from the crankcase to the PCV valve itself). I have first-hand experience with that.
3. It has a thicker gasket that compresses more than the one designed for the magnezium valve cover, which should provide a longer service life.

Their only downside in my view is the potential of cracking due to overtightened bolts, since their failed, integrated PCV valves can be replaced and glued back with the right kind of industrial-grade glues.

Most important thought: work on your car by yourselft if you can. Even the most highly-rated BMW service shops will sometimes screw up and try to cover up their mess. Especially if they have no ideea on how to fix what they screwed up, leaving the owner of the car to find solutions for almost impossible to solve problems.

[VinnyK]

Im about to do this to my n52 as well. 2 recent valve cover gasket changes, still leaking oil into cyl 1 spark plug hole. Im assuming my cover is toast. Gonna replace it and drill out the same broken bolt as yours haha. Might just jbweld a stud and use a nut to clamp it down like what you did. Thanks for the guide!!!!!!