How do I convert a Chevy 502 ht into marine application
 

Hello all I have a 1997 24 baja sport with a blown 454. I have a brand new 502 ht in a crate and would like to put this in my boat. I spoke to a few people and they say to switch cam and install stainless head gaskets. Does any one know if this is true are the heads the same can I just install a mercruiser 502 cam and sis head gaskets to be okay. Any help would be appreciated Ty

Besides the cam you also change the valves.

Brass freeze plugs

Check proper clearances for rods rings crank. IMP roller rockers. Oval ports unless your 6500 or more. I'm not a engine guru but someone like Bob Teague would have the gospel
Good luck

You guys are missing the biggie that will lead to sure engine meltdown if not addressed - the oil bypass valve in the oil filter pad. If you leave the 11 lb automotive valve in there, and run the remote filter and oil cooler and lines like most boats have, the bypass will open and the oil will bypass the cooler and filter, sending hot dirty oil through the bearings and resulting in an premature demise for this engine. Lots of threads on here about this if you do a search.

The exhaust valves should be inconel to last in a marine application. Cam could be ok what are the specs? Roller lifters should be Morel or other endurance rated hydraulic. You should check out the valve springs also, I am running the ISKY Tool Steel springs. Oil bypass definitely, good catch on that one. Bob Madera would be the first call I'd make, he will set you up with the right parts to make sure what you have will last.

If you are staying with a stock GM cam with moderate lift, you may be fine with the stock lifters and springs. Most of their cams are barely over .500 lift - for instance the stock 502 MAG cam comes in at a wimpy .483 lift. These engines commonly run 600-800 hours on those stock lifters. Now if you are planning to swap to a healthy lift approaching .600 lift, then I completely agree that a quality lifter like the Morels with the .750" wheel is best. I think the HT cam is relatively mild, designed for towing, and has a fairly wide LSA that would probably work fine with stock exhaust, but double check the specs to be sure.

Inconel valves are definitely a good investment, especially if you plan to run the boat hard in the 4K-5K RPM range, and they are an absolute must if you are supercharging. The stock 502 reciprocating assembly probably has a steel crank, 4 bolt mains, and the better 7/16 bolt con rods, so you are probably OK there. You will want forged pistons if you are going with the blower.