The stem of the end of the valve was worn.

The rocker arm was worn

The valve seats were worn.

The valve face was worn.

It is actually a common problem especially in older bikes that the valve seat wears(or valve) and then valve recesses further into the seat which then the valve is able to contact the rocker arm thence holding the valve open and a loss of compression. For something as new as yours...seems too early for that problem.

 

Valve clearances that are too tight will cause the valves to open before combustion is complete within the cylinder. Over time this will damage the edges of both the valves and seats so that compression is lost.

For this reason, most mechanics prefer to adjust valve tapping clearances when the engine is cold, knowing that they will loosen once the engine is warm. Valves that are too loose will only create a small loss in power by the valves opening a little late during the intake stroke.

 

My 2000 300EX is 8 months old and has had all routine maintenance done to it. Just recently it lost all compression and would not start. When I took it to my local Honda Dealer he said I had probably sucked dirt in through the carb or airbox and had scarred my piston and ruined my rings. I took to a good friend of mine to have it tore down. When he checked the valves they were tight and weren't seating properly causing the loss of compression. He said in 20 years of wrenching of 4 strokers he had never seen this before. Do any of you out there know what might cause this? Any help would be appreciated.