I bought a 19,000 mile winter project bike. It calls for 6000 mile adjustments. The valves had never been adjusted.
The bike ran and shifted nice once warmed up with no smoke blowing on acceleration or deceleration. It felt strong.
I thought I'd check the compression before checking the valves (push-on type tester). Three cylinders were low, one cylinder was real low. Not good.
So I checked the valves all eight were way out of spec. Two were acceptable, three were almost tight, three were so tight I couldn't get any feeler gauge in at all. The tightest was on the offending low compression cylinder.
I adjusted all the the valves to the loose end of the spec.
When my friends asked me if I rechecked the compression, which would surely have improved, I told them NO!
I didn't want to know. The bike starts and runs perfectly, it's quiet, there's no smoke at any RPM and it feels at full power.
Moral of the story... If I'm happy the way it runs and is not showing signs of trouble..I'm not gonna go looking for any.