Originally Posted by caponerd
...soft valve seats. If it's still running past 50,000 miles, it means the problem has been addressed.
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.