I have a 2002 GS500 that was getting low to no compression.  After tearing everything apart the exhaust valves in both cylinders were stuck open.  After wrestling with the exhaust valve buckets, I discovered that both of them were out of round.  Anyone have any thoughts of what could have happened to only the exhaust buckets to screw them up?  The camshaft looks fine.  Both valves were bent, but I'm assuming that happened from running it with the valves stuck open.  The holes in the head for the buckets look fine, as the intake buckets slide in and out of those holes without a problem.  I'm replacing the buckets and valves, just curious as to what could have happened that would throw those out so it doesn't happen again.  The valves were adjusted about 3,000 miles ago.  Anyone have any thoughts?

Thanks.

How many miles on your 02 GS?  I bought a 02 used with about 4k miles on it and one of the exhaust valves was sticking open when the engine was cold due to a sticking bucket, discovered it when I did the first valve clearance check at approx 10k miles.  The tight bucket would loosen up in 30-60 seconds after starting and the engine would then smooth out and run fine so I let it go like that thinking I'd fix it when it no longer loosened up quickly after starting or maybe it would wear in and free up.

Well I had no problem with it at all until one freezing cold winter morning I cranked the engine and BANG!  The sticking exhaust valve broke and locked up the engine at about 21k miles.  I pulled the head and replaced the exhaust valve and both exhaust buckets with ones from a parted out engine.  Buttoned it up with new gaskets and it's been fine since.  Now with over 54k miles it runs better than ever and I expect to get the 80k or more miles from it I got from the 97 GS with no further engine trouble.

My sticking bucket was not out of round, it was just too tight in the bore and I've always assumed it was fit too tight at the factory.  I measured it all around and up and down with a 1-2" micrometer and it was just a bit too big and not out of shape.  Yours is the first other case of a sticking bucket I've heard of here and also on a 02.  Interesting.

My valve check records show the intakes wear little if any and the exhaust valves tend to recede into the head as the miles add up and one was down to a minimum thickness shim on the 97 GS at 80k miles when I replaced it with the 02 GS:

http://img.photobucket.com/albums/v443/jcp8832/valveclearances.jpg