500 carb

[Tony M]

At what hours should motors be rebuild

[MERPerformance]

The time on rebuilds and or inspections of the valve train depends on type usage of boat, engine type and parts used in original build.
Do you run in fresh water.
How often do you change your oil.
Have you had any mechanical problems.
How hard do run the boat.
What parts are in the current build.
Are you wanting to up-grade with more power.
If you are running 500 HP, I would say, if you have 500 hrs things are getting to there limit. I would start with a compression test first, then narrow it down to a leak-down test. If your leakdown is good, lifters& valve springs would be the next concern. Don't overlook the exhaust system, if you are able, you need to pressure-test them.

[jeffswav]

I have heard that the valvesprings are prone to failure in the 250Hr range. Like MER said the engine itself should be refreshed in the 500Hr range. When I did my Roller Cam upgrade I used the Isky plus springs, they are much better than stock.

[Griff]

Valve springs at 200hrs and a leak down test.
Leak down test at 300-350hrs and probably top end refresh.
Leak down test in the 500-600hr range. Probably need a complete rebuild.