Some of the big shops around me won't crack an engine open. Labor at $100/hr and 5-6 hours to remove, diassemble, clean, inspect, replace parts, reassemble, reinstall and WARRANTY the engine makes it more cost efficent to replace the engine. I am probably half what a big shop charges but that is still more than some folks is reasonsble. I like to change the head gasket at the same time so it winds up being head, valve cover and case gasket, oil filter and oil, spark plug and camshaft at a minimum for parts. It probably needs an air filter and fuel filter, the blades sharpened, the deck scraped out and the front end greased. So the $100 camshaft turns into $500 or more to get it "mow ready".