Looking at a 2001 boat that has a pair of hp500efi with 190 hours.Question is how many hours before you have to do a rebuild on them?

top end should be looked at around 250-275, the valve springs are what you need to check. But a complete rebuild is 500-700 hours. But all this depends on you maintance and how you run the boat.

mine have 550 hrs. Recent compression check by Performance Marine Service of Lake George, NY didn't show any problems. John recommended "refreshing" the top end at 700 - 750 hrs. He estimated about $7000.00 for a pair of Merc Blue Motors, if you did it before you started having problems.