Did my heads on both engines 2 seasons ago. cylinder walls looked awesome. Compression check 160+ across the board. For some reason the machine shop left the exhaust valve oil seals out. The intake valves have them I guess it keeps the guides lubricated better. Did this at 500 hours. I use Amsoil 20-50w Zrod oil only. Very High Zinc oil and I change the oil every 25 hours and soon as it starts to turn a darker color. Engines run great 509's 500 HP each. I do get a puff of smoke on start up when hot because of the valve seals not installed but only for 10 seconds.