If i replace a mercrusier 350 with a regular 350 block will it hold up in a boat??

Question

im looking to buy a boat and looking at one with a shot motor im wondering if i replace the mercrusier 350 with a regular 350 out of a truck if it will hold up or is there a difference between them

Answer 1

If you are going cheap you could do it.   A marine engine has a different cam in it. A boat motor is designed to run at a more of a constant speed.   The freeze plugs are bronze, so they don't rust.  That might be something you need to look into.  Some of the external parts are different.  The ignition should be marine grade.  The exhaust manifolds, water pump, the alternator, starter,should be marine grade too.  Marine grade parts are expensive, but will always last longer than auto parts.  Make sure that there will be nothing that could send a stray spark.  Good luck

Answer 2

Yes you can. My Uncle did put Chevy 350 in his four Winn. It was Volvo 4 cylinder engine. It ran good. But you need to have mercrusier exhaust manifold. water pump. because  the engine will take fresh water from lake or what else. it will make corroded on water pump, etc.  Regular car/truck have antifreeze that prevent from corroded. Just replace the block and use other parts put on from original boat parts.

Answer 3

You can, but just as docmetal has stated it will rust out every few years.  If you are a mechanic like he is and you like replacing engines then go for it.

A Merc 350 has one part that is the same as a Chevy 350, the block.  Everything else is different.  the block is also treated differently Designed for marine use.  It's not just about corrosion.  A boats engine runs at a relatively constant rpm.  Since there is no shifting like a car, acceleration and deceleration are slow and gradual. The valve system is designed for this type of power.

I was at my boat shop and a guy was complaining that his alternator keeps failing. He had a 2002 merc. He was going to pepboys and buying an alternator for a 350 truck.  It fit just fine so he figures it should work.  He keeps saying its the same engine and the clerk just smiled away as the guy was complaining.

After the guy behind the counter explained to him that they are not the same, he bought the alternator made for his boat.

I was trying not to laugh as I waited listening to this guy.

Answer 4

Yes, and no.  When mercruiser built your engine, they did use a standard chevy small block.  However there are differnces past that.  Due to the constant load the engine sees (like driving a car up a steep hill in overdrive all of the time), it needs to have different cams, to produce more lower end torque, and if the engine is carborated (sp?) it will have different rods, and jets than a std. engine.  On marine engines you will usually also find heavier duty parts (rods, bearings, bushings, seals, pistons, wrist pins, etc...)

This is not to say that you CANNOT do it.  The current engine in my boat is likely an automotive engine (the block and heads are GM colors, and not Volvo Penta colors), and once the carb was correctly rebuilt to marine specs, has run fine.  

So I guess I did not answer your question, but hopefully I gave you some information that will help.  When you say "shot" motor, what do you mean.  It may be worth rebuilding only what is "shot".

Answer 5

OK... a 350 is a 350... BUT!

1. Marine blocks use marine-ratted cylinder head gaskets (they are stainless steal to prevent rust).

2.Marine blocks use brass core (freeze) plugs instead of the stock tin plugs used in autos.

3. Marine engines are expected to run at or near full throttle most of their lives and for this reason have a special camshaft profile to alter the driveabilty of the engine. (You can use an automotive cam... but don't expect the same performance.)

4. Marine blocks are specially electo-deposition painted to protect them from water and electrolysis corrosion.

5. Marine blocks (most) use cast iron cylinder heads in order to prevent electrolysis and dissimilar metal corrosion from occurring between the block and the heads.

6. Marine engines use specially modified water circulation pumps (also corrosion resistant).

----Most of these mods are done to decrease corrosion as boats are exposed to water in stead of rust preventing coolant. If you do use an automotive block you need to make these modifications and by that point it's easier to just go marine; but if you use that bock do yourself a favor and get the right gaskets and core plugs and swap um out. You can get both at any boat dealer, shop, or average everyday machine or parts house. If you “stuff” an automotive block in a boat without modifying it WILL corrode in a mater of years or less and you will have rust, leaks, oil-in-water, sinking boat. Etc.

Bear in mind that while the blocks can be made to interchange the other parts on the engine CAN NOT!!! Especially the electronics which, on a boat, are "spark sealed". The use of automotive parts is just asking for a fire..... and a boat is a VERY serious place to have a fire!

Answer 6

as stated before the block will fit but as most people stated the engines are different in many areas I wont rehash the differences but would like to ad an important one overlooked   legality       auto engines and parts are not  uscg approved  as well as auto starters, carbs, and alternators. you would be placing yourself in an illegal situation if someone got hurt or killed. there is also criminal penalties depending on where you live not to mention that it will not be covered by insurance or the manufacturerer if a accident occurs  you will be left holding the bag  because you have now become the manufacturer since you have disregarded the factory specs.(saw an explosion once due to an alternator) guy got 5 years manslaughter huge fines plus a dead friends daughter  in the big picture original is cheaper

only use approved parts   anything else places you and other people in harms way and is irresponsible boating  any dealer that uses non approved parts is also accountable

Answer 7

Absolutley a 350 is a 350 . I have put just any  350 chevy in my  Owens they all worked good . I bought the last one from craigs list . I have had the boat for 29 years  and have changed motors countless times  they all rust out  so the cheaper the better . I can chance an engine in one weekend  . buyimg a new motor is piontless The used ones rust just the same as the new ones  when the head  gaskets blow and there is water in the oil overboard they go .weather they are the same cam pistons  ECT I do not care RPM is RPM  watch the tach it is all good  . Remember  Cheaper is better .

Answer 8

Marine engines run under much different conditions than an automobile. You are constantly running under load, there is no coasting down a hill in a boat. And they cruise at much higher rpms than you drive along in a car. One of my boats and one of my trucks has the same 5.7L engine. Cruising along in the boat is about 3000 rpm, in the truck i rarely cross 2000 rpm driving down the road.

Therefore, marine engines are built to much higher specs. Harden cranks, tougher cams, tougher valves, rods, etc. You get the idea.

Maybe take the 350 block and rebuild to marine specs?

In response to GW: MercCruiser and many engine manufacturers don't recommend running at WOT for 95% of your boating day. Keep your top cruising speed at 80% of WOT, your engine, and your gasoline CC will thank you.

Answer 9

Yes, a GMC 350 will do, but you have to make some modifications.  Freeze plugs should be changed to brass, the water pump must be marine grade, the exhaust risers and manifolds should be marine grade, and you have to make sure the rotation of the drive shaft is compatible with the outdrive.

Answer 10

350 is 350. The only difference is the exhaust manifolds,distributor and water hose setup. I have a 350 cu. in. -330 horse in my Crestliner Crusader and it is just fine!

Answer 11

there is a reason they have marine blocks.

Answer 12

To everyone that has answered this question...think about what your saying before you say it ok? Because you can confuse people. All of you say you can put one in. Yes you can. GM engines are all built on the same platform regardless of size. BUT there is a difference between an automotive and marine engines. Everything in a marine engine is marine grade. From gaskets to rings to bearings. Everything. The one guy that uses the name "docmetal" is crazy. He claims that he has changed engines coutless times?? Why?? Because he is using the WRONG engine. Engines regardless of the application if properly maintained will last 15+ yrs. Why marine engines are different? Because when a car runs at for example 55 mph the average engine rpm is around 1900 to 2200 rpm. A boat running at the same speed runs around 4900 to 5500 rpm. For which boats run at or near wide open throttle 95% of the time. "Docmetal" is wasting money. If he would just install in RIGHT engine in there then he wont be changing engines all the time. UNLESS he ENJOYS changing engines all the time. So the answer to your question....NO. If you remove a marine engiine go back with a marine engine. In the long run you will have more enjoyable yrs out of it without having any trouble. IF properly maintained. Thats the key. Hope this helps.