They do have a serious flaw though. The SOHC heads require a very long, very heavy timing chain, which is common on German cars of the 'investment' grade, which drives the valve and ignition timing. The chain is guided and tensioned by a number of plastic guide rails. These are consumable items, since they are friction surfaces, subjected to wear by having a heavy steel chain under tension dragged over them at 1/2 the engine's RPM. I've seen some worn through to the aluminum backing underneath, which means bits of aluminum and plastic have ground off into the sump, and that the timing is waay off, chain probably wearing badly, etc.
This would be a problem on engines with bad cam oilers, bad chain tensioners, people not getting oil changes, bad/wrong oil, other simple things like that which shouldn't happen to a well maintained car. However, these were built more than 25 years ago, and nobody knew then how long the engines would be used or what time and chemical breakdown would do to the plastic guide rails.
BTW I don't think anyone had trouble with the rails in the 80s, not at least like they did with the weak single row timing chain on the 380 engines, which was later replaced with the double row chain.
Long story short, the guide rails will get brittle and break off, fall down into the timing cover and get stuck between the chain and teeth of a cog. This will destroy the engine beyond any reasonable repair, as the timing chain can jump a few teeth, break, or otherwise cause valve/piston interference, after which you will have nothing left but a block that may be salvageable.
In the above picture, the front timing cover is off, exposing the crank timing sprocket, idler, tensioner (left side) upper guides (white plastic sticking out of the heads). This engine has been conveniently pulled out of the car..
I think the labor on changing out all of the guide rails (at a good mechanic) will come to around $7k, plus all of the "While you're in there" shit that you'll want done, somewhere around $9k.
I didn't have any power problems or slapping noise at startup, or any indication that there was anything wrong with the engine except that I hadn't actually opened it up to take a look. That could have been a bad engine blowing mistake.This is where it pays to know what you're getting into when you buy a used car. Know EVERYTHING about it. Become an expert in that model before you buy it so that you know what to ask, what to look for, how much it will cost to fix (time+money), whether or not you can drive it or have to trailer it home.
The above sequence shows what the guide rails look like when they've failed. It just broke in half, one half of which is bumping around down there on the ignition sprocket, just waiting to get chewed under..
A new set of guide rails (upper only) costs about $18, and they're white as the driven snow, unlike this one, which is brownish-oil colored, indicating it's chemically transformed over the years into a fragile, brittle time bomb.
To swap out the upper rails took about 4 hours, including the 'while your in there' shit, but without removing the front cover and getting at all the lower rails. The timing chain is showing no stretch, which is nice and unexpected, the timing gears aren't worn any more than they should be at this point.One thing that's a concern with certain engines is one wearing part being of a dissimilar material or less wear resistant than the part wearing on it. For example the cams and sprockets are cast iron, but the chain is an alloy suitable for chains, the lifters of a hardened steel like 4150 or something even harder.
Of course all these parts are protected by a sheet of oil, but it's not a 100% friction barrier in any case.
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