525 Durability?
 

How long until rebuild or refreshen on average??

No one knows because after about 200 hours the headers fail and trash the motor, so you have to rebuild or replace. My buddy's lasted almost 350 hours then had a dead rear cylinder on each and had to be rebuilt.(After 6 header repairs) It was just head/valve damage, the bottom end was in pretty good shape.

I have a friend up in Jax with another 29 who has 350hrs on his and NO problems at all. I'm told that the bottom end is good for up to 500 and depending on how hard the motor is run, replacing the valve springs every 100 to 200 hrs is about normal. As far as the headers go, I'm told that all the problems occur in saltwater machines. I always flush 10+ minutes with Salt-away and drain the headers after. So the boat sits "dry" between uses. I've had no problems so far. I think if cared for right, it's a very durable motor.

A leakdown test will tell you alot about what's going on inside the motor. If you do themevery 50 hours on mild performance engines you can chart deterioration and pretty accurately predict your rebuild points.

I'd do valve springs at 150 and a top-end at 300- replace the rocker arms then too