Yes fine, "VANOS, cams of fate"

I'd like to start by saying that Mouser is responsible for the name of this post.

The reason I'm talking about VANOS again is that it turns out that the VANOS unit on the 3 is pretty damned broken. And before I get into how badly this broken VANOS unit has ruined my day, I'll tell you what the hell this whole V-A-N to the O-S is really all about.

The whole mess starts because at their core, all engines are really compromises. Engines in typical road cars generally involve compromises between things like fuel efficiency and low-end power. Big diesels in pickup trucks typically trade a bit of huge power output for a hefty slice of durability. Even race cars (which we generally think of as nothing but pure horsepower beasts) are really just the right mix of power production and light weight. The point here is that engines are rarely designed to be the biggest or the most powerful simply because that wouldn't fit under the hood of your typical automobile.

One part of the engine that's heavily affected by compromise is the valvetrain. The valves allow unburnt air and fuel to enter the cylinder, and they let it back out after it's been turned into exhaust and heat and noise and other goodness. The valvetrain on a typical car is engineered to work really well at idle and at low speeds—the type of driving that a lot of us do every day. In contrast, a typical race engine trades that smooth idle for better higher end power. We all know what a dragster or other serious racecar sounds like when it's idling, right? It's noisy and lumpy and doesn't behave terribly well. It certainly wouldn't look good to have that sort of brash drag car idle on, say, a Honda Insight.

That's where variable valve timing comes in. It allows the engine to shift from a smooth-running cam timing at idle to a more aggressive timing at the top of the rev range. The idea is that you get smooth idle and good low-end power without throwing away the possibility of having high-end power, too. You know-it-alls in the audience will recognize a few implementations of variable valve timing. Nearly every major car manufacturer (OK, perhaps not Daihatsu) has at least one: Honda has i-VTEC, Toyota has VVT-i, Porsche has VarioCam, and yes—you guessed it—BMW has VANOS.

Now, all of these implementations work differently, so I'll only tell you about BMW's. The idea behind VANOS is that just like in any overhead-cam engine, the crankshaft has a sprocket and a chain which heads up to the cylinder head. Instead of driving both camshafts directly, however, the intake camshaft has a little gadget attached which allows the sprocket to be rotated a few degrees around the axis of the camshaft—the idea is that the engine can then turn the intake camshaft so it runs a few degrees ahead or behind the crankshaft and exhaust camshaft.

This is a bit of a simplification—there are actually two cam chains and the "little gadget" which allows the intake phase adjustment is a really cleverly designed helical gear arrangement controlled by a linear actuator and a few shim plates. The diagram at the beginning of this article is, in fact, a "single VANOS" unit from a BMW M50 engine—much like the one in my 3.

My point here is that yes, VANOS is awesome, but it's also a complicated piece of machinery. And it's so complicated that it's going to cost me close to two grand to replace.

Admittedly, it's only $1700, and they shop is going to replace a bunch of other stuff while they're in there, too. I'm going to have them clean up the whole cooling system and so forth while they've got it all torn apart.

So there you go—now you know what VANOS is, and why it costs me a boatload of cash.