Originally Posted by Wirespokes
Actually, the problem was valve seats that were TOO hard and didn't transfer the heat from the valve to the head well enough. The BMW engineers were anticipating unleaded fuel and changed the seat material, and they didn't guess right. By the middle or late 80s they got it right.
One solution is to run with a bit wider clearance during the heat of the summer - instead of .008 on the exhaust, got to .009 or .010. The intake isn't normally a problem so leave them at .004. Just pay attention to them and you'll see if they're losing their clearance. There's usually no big rush to get this done, but the sooner it's done the better chance there is of saving the exhaust valves. And they aint cheap, believe me.
Read all about it from Snowbum - he's got a lot to say about this. Lots of background info there.
I stand corrected. I do remember hearing that it had something to do with an attempt at preparing for unleaded fuel.
I can attest that if the seats have been replaced, the replacements are amazingly stable. I bought my 1982 model in 1999, and after putting around 50,000 miles on it, I've only had to actually adjust the valves a couple of times. This one had been done at around 30,000 miles, and when I got it, it had about 70,000 on the clock.
I check them regularly, and they're almost always within spec.