How many hours before 502 rebuild
 

New to offshore but can anyone tell me how many hours a 95 502 mpi can go mine has 485 hours.

We have over 800 hours on the stock 502's in the Carver and they still run like new. Granted, they hardley see above 3000 RPM but a stock 502 should be good for a while.

my guess on a speed boat was also 800 plus or minus...

Maybe a valve job, springs and head gaskets in the next 100 hrs. Shouldn't need a full rebuild until around 1000hrs. Have a compression and leak down test to see how healthy it is.

My original 454 MAG is a very similar build it it went over 800 hours on the bottom end. We wnt through it when it came out for gimbal ring replacement. Everything looked good. As Griff said, upper end might warrant a little attention.

Thanks guys i hope my dead clynder is a valve problem and i can just do upper.

I had a exhaust valve stick on cyl 1 at about 60 hours, pulled the heads and had them re-done. I had to purchase a new valve and obviously new gaskets and head bolts, did the work while the engine was in the boat and it cost about a grand after everyting was said and done. I now have 522 hours on the boat and still running good.

I always wondered what caused the valve to stick like that, it actaully bent the valve stem but luckly didn't stay open enough to damage the piston. The previous owner had the stock exhaust manifolds that had leaked which I think caused part of the problem. I was also told cyl 1 can sometimes have a issue with getting enough oil because of the angle the boat runs. I did upgrade the riser and manifolds to afer market
which probably helped.

Good Luck, Jim

Had 630 hours on my old single 502 boat when i sold it, no issues.

Engine life is far more dependent on fuel burned than hours. 20,000 gallons is probably about the number for a big block. I burn an average of 10 gallons per hour, and mine are very tight and essentially perfect at nearly a thousand hours. Supercharged and run hard, maybe 100 hours.