Marine vs non-marine engine....

[SmurfOnAGixxer]

Can anyone tell me a reason why a non-marine engine would not work in a boat? I know the spark proof ignition system and special starter and alternators. But main long block wise, what would I need to change in a non-marine motor to put it in a marine application?

Thanks

 

[Chris E]

cam shaft is different as well, marine engines run at higher rpms than car motors

 

[SmurfOnAGixxer]

cam shaft is different as well, marine engines run at higher rpms than car motors

Sorry, camshaft as well, I did know that. But there is nothing different in block design that would pose a problem is there?

 

[Chris E]

no, a block is a block, the internals and externals are different, but the blocks are standard GM truck or industrial motors

 

[onthehammer]

Big difference! On a long block the main differences would be head gaskets, valves, ring gap, tolereances throughout the entire motor. Not saying that it wont work, just wont last as long or perform as well. highly recommend a marine long block.

 

[supergenius74]

I agree with onthehammer, I have known a couple guys who did the car motor in a boat replacement, and even though it seemed to work great the motor only lasted a year or two at the most before they blew. I don't know all the details but I believe there is enough difference to make it worth your while to do it right. As many have said, driving a boat is like pulling a trailer up hill with the AC on and flooring it. -shane

 

[Old Navy]

I just saw an ad in the "free" autotrader that Berger Chevy in Grand Rapids, MI has got some Marine small blocks on clearance (long blocks, I think) prices looked good.

 

[winter]

I cant speak from experience, but as mentioned, the internals, while they appear the same, as different to the degree that they are used in hi-load conditions. It was told to me that the 427 chevy used in the early 70's through early 80's medium duty dump trucks had completely different guts than the 427 used in the corvettes and other muscle cars of the late 60's. That was due to the fact you are hauling a heavy load, foot flat to the floor most of the time.
The blocks are identical i beleive, from marine to non-marine and i do not believe there is any coating or protection for the marine aps. either. I'm likely going to have a new motor built this winter but will not even consider an automotive mill or parts. I'm leaning towards a well known builder who has experience with boat engines, but i may spring for a long block from Chevy.

 

[boatman4021]

This topic has came up several times and still yet, no one has been able to give solid proof that the sort block is any different besides for brass freeze plugs and the cam. Are we to believe that Merc. buys brand new short blocks from GM and then rebuilds them all? I have a friend who took the 350 out of his boat and replaced it with one from a car which he freshened up first. His plans were to rebuild the "marine" engine and put it back in the boat because he was told that the car engine was different and would not last. All that was wrong with the marine engine was a bad rod bearing and it had a light knock. After tearing it apart, he found the same crank, rods, pistons,and rings as the motor that he had just put in the boat. 5 years later and lots of time pulling the tube and running flat out, it's still going strong. My advice would be, don't just grab a well used car engine and stick it in your boat Do it right and rebuild it first! boatman

 

[Big Red]

Most people prefer on a bottom end 1 piece rear main seal. I would run a set of forged pistons and a decent set of rods. If not take your basic rod's and have them shop peen-ed. A Steele crack is the best way to go but not all marine engines have them. Use brass freeze plugs and a good set of marine grade head gaskets.

The cam and head work gets tricky. Your heads need to be built around your cam selection. A marine cam is the way to go. A boat needs torque more than hp. A good set of S.S, valves. Your head work needs to be done and set up by a qualified person. A lot of power will be lost here if it's not done right.

For clearances I feel are no different A forged piston needs more cyl. clearance than a cast piston because they expand when they get hot. Your crank, Rod, cam bearing, and valve guide clearances are all the same. For a racer you tend to build it a bit loser for quicker rpm's but your rebuilds come more often.

A lot of the 427 truck engines where tall deck blocks which where useless in a car application trying to covert pullies and brakets to make it work. I have one for 500 if you wan't it. As dodge also made two 413's which the tall deck was used in truck application.

 

[wca_tim]

what's said above, especially what Red said is dead on. If you want something to just run and aren't worried too much about performance, a car engine with different head gaskets, freeze plugs etc... will work, but if you want more power AND want it to last you need different internals and different clearances... especially on the bottom end - everything from component choice, bearing tolerances, etc. to seeming "details" like piston ring end gap clearances, port matching intake and heads, etc... the heads and their set-up being the key to making good power (matched to right pistons, quench, compression ratio, cam, intake, exhaust, etc... of course) is also dead on. A good engine builder is truly an artist, and good marine builders with real experience are hard to come by, but the product of a well thought out build by an experienced shop is a world apart from what winds up in most boats.

Sure you can pull skiers around behind a car engine... but there is no comparison between a well (re)built marine engine and a car engine.

just my two cents / experience