Cheap insurance: Why our BMW received a crank seal guard

BMWs are 100% reliable, if you fix everything that breaks.

That sage advice comes from our old friend, Rennie Bryant of Redline Bimmer, a longtime South Florida repair shop.

This phrase really captures the reality that BMW generally builds stout, capable, well-engineered cars capable of lasting hundreds of thousands of miles–but that there are also some disasters waiting in the wings that could derail your fun.

When we originally sketched out this project car series, we had a slot marked for “reliability mods.” Now it looks like that slot is going to turn into an ongoing series.

We don’t want you to take this as a shot across the bow of BMW reliability, though. We still stand behind the stout and well-built statements, but we also know that some preventative reliability work up front can save us from occurrences down the road which could lead to serious financial and logistical repercussions.

Belt Go Bye-Bye

You may recall that our first trip to the track for baseline testing ended in a broken serpentine belt, likely due to a failing bearing on the idler pulley.

[Surprise: Our BMW 435i broke a belt during its first track day]

Serpentine belt breaks are a not-uncommon occurrence on these N55 engines, but they can usually be traced to oil leaks contaminating the belt and weakening it prematurely.

In our case, our oil filter housing gasket is holding strong, but we do have a weepy oil pan gasket, so that could have aided belt breakage as well, although that pulley was clearly ending its own life.

Regardless of how the belt fails, though, that could just be the beginning of your problems. Many BMW inline-six engines–our N55 among them–can experience a failure so ridiculous that it feels like the engineers were playing a prank.

After a belt breaks, its shredded bits can get pulled behind the crank pulley where they begin to wind around the snout of the crankshaft. As more and more material collects, the frayed bits of belt can end up getting pushed right through the crank seal and into the oil pan.

If “bits of shredded belt in your oil pan” sounds bad, it’s because it is.

Best-case scenario is you quickly notice the failure and turn off the engine, ideally before any chunks get stuck on the oil pump pickup screen.

Worst case is those chunks blocked flow to the pump for an extended time, or even were drawn through the screen and circulated through the engine.

How to Prevent Catastrophe

In any case, it sounds like a failure that was made up by mean adults just to scare kids, like of a BMW version of “You’ll shoot your eye out.” But it’s all too real, as posters on our own message board have pointed out after having the unfortunate event happen to their cars.

In our case, we were lucky. The belt slipped off the front of the pulleys and never got drawn behind the crank. Still, rather than simply replacing the belt, we decided to buy some mechanical insurance in the form of a crank seal guard from Vargas Turbocharger Technologies.

BimmerWorld turned us on to this $79.99 guard, which is their favorite for protecting N54, N55 and S55 crank seals.

“It’s just kind of a no-brainer,” says BimmerWorld’s Phil Wurz. “We kind of see it as basic maintenance for these engines, since it’s a low up-front cost that can save a very high back-end bill in the event of a failure.”

The Vargas crank seal guard installs easily with two bolts. Unfortunately, accessing those two bolts, like so many other things under the hood of modern BMWs, takes plenty of patience, specific tools and lots of creative profanity.

If you notice that the photos of our installation aren’t that great, it’s because you have little to no chance of even actually seeing most of the fasteners that you’re working on. You’ll be doing much of this job mostly blind, and this is also the part where you’ll start to believe that BMW actually stand for Buy More Wrenches.

You’ll need some specialized tools for the job–most of the fasteners involved are external Torx heads–but mostly you’ll need exactly the right combination of ratchets, sockets and extensions to properly access the crank pulley bolts to remove them.

We found the best access to the front of the crank pulley to be from below, although if you have arms longer than our flappy little T-Rex stumps you may have better luck from above after you remove the intake plumbing.

But from below, once you remove the lower engine cover, then the supplemental cover guarding the steering rack, you have a nice little slot to get your hands in to the front of the crank pulley, right between the pulley and the fan shroud.

After removing the serpentine belt, you’ll need to remove eight E12 bolts to free the crank pulley from the front of the crank. The trick here is the bolts are recessed into the pulley, so you need a bit of extension from your ratchet, but too much extension will push the ratchet into the fan shroud, limiting access.

You’ll also need a fairly long ratchet to get enough leverage to break the bolts loose and retighten them. A shorter ratchet will be fine for the bolts clocked to the bottom of the pulley, but the upper bolts won’t be as easy since all of your “swing” of the ratchet needs to be below the car. There’s not enough room off to the sides of the pulley when accessing from below.

We ended up with a 12-inch long, ¼-inch drive ratchet with a flexible head. The ¼-3/8 adapter, plus the depth of the 3/8-drive E12 socket, was enough to reach into the pulley but didn’t protrude so far as to interfere with the fan shroud. Certainly, other combos would work, but the takeaway message is unless you have a mad huge assortment of socket depths, wrench lengths and thicknesses and extensions to choose from, budget some extra time. You may need to make a run to the tool store of have something overnighted from Munich to finish the job.

Likewise, once you remove the crank pulley and clean everything thoroughly with some degreaser, removing the stock bolts holding the timing cover and installing the seal guard with the supplied hex key bolts takes some specific length extensions as well. You’re in another not too long/not too short situation here, and ¼-inch drive tools, or thin-wall 3/8 drive, will give you a bit more room to access the fasteners.

So, it’s frustrating, and a bit time consuming, but ultimately worth the hassle as this $80 part plus a couple hours of skinned knuckles can save thousands of dollars of potential disaster down the road.

Next time on reliability theater, we’ll discuss the ins and outs of fragile BMW charge pipes. Let your hands heal from the crank seal guard and we’ll dive back in for more blood-soaked adventures in reliability.

When is a broken belt more than a broken belt? When it gets suck into your oil supply, which is totally a thing on some BMW inline sixes.

The Vargas crank seal guard is here to help, though. This small, clever shield covers the exposed crank seal behind the crank pulley and prevents foreign object intrusion.

Getting the crank pulley off can be frustrating, though. This is the best picture we could get using a phone the size of a deck of cards, so imagine what it’s like getting your big meaty hands in there. Patience, calmness and lots of wrench and extension options will be your friend here.

Our secret weapon was this foot-long, ¼-inch ratchet. It gave us the leverage we needed and the adapter plus the socket gave us just enough extension.

Looking at the exposed crank seal, you can see the potential issue: That channel can pack with debris, then get pushed right into the sump.

With the crank guard in place, though, there’s no more gap. We dare our belt to break now (not really).

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