The local FBO just had two exhaust valves go bad on his C180.... Pulled
the cylinders and sent them out to a cylinder shop for overhaul... They
came back yellow tagged... He re-installed the cylinders back on the
same piston they came off from, and on one could not get the exhaust
pipe to line up... What the hey? Gets out a strong light (why do all
mechanics work in a shop that is dimmer than a confessional booth?) and
takes a look... The head was re-installed on the barrel ten degrees out
of alignment...

I just went through a big thrash on a carburetor that was supposedly
zero timed from the re-manufacturer... It was defective out of the
box, TWO times in a row...

So yellow isn't necessarily the answer...

denny