7.4 Engine Swap
 

I have a 95 7.4 mercruiser with a cracked block, everything else seems good, has anyone had any experience with putting an engine out of a automobile in a boat? I was going to part the boat out but looking at 1995 automobile 7.4s in my area are relatively cheap compared to the mercruiser. I know ill have to put in brass freeze plugs...but im wondering as far as the engine balance, manifold bolt ups, if the 7.4s are interchangeable? Im doing this solely for cost as the mercruiser stamp on a 454 seems to be worth its weight in gold!! just curious as to what I need to look for or what I may be getting myself into, Thanks

Re: 7.4 Engine Swap
 

The blocks are definitely interchangeable, I would say the heads are too unless they had different accessory mounting holes. If your manifolds and heads are good, I'd just swap the block out. I would almost bet money they prob are identical. You could always match casting numbers also.

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Re: 7.4 Engine Swap
 

I had a 97 350 Merc with a cracked block and I put JB weld on it. It held for several years. I sold it to a friend and he finally put a block in it this year. It ran about 7 yrs like that. It was and open water system so the pressure was around 5lbs. That is a cheap easy fix depending on your cracks...

Re: 7.4 Engine Swap
 

I wouldn't recommend it. Auto engines are NOT boat engines. There are many quality marine engine rebuilders out there, even a lot of used engines, and there are good deals to be had. Sure, you will pay a little more than your standard auto engine rebuild for a marine engine, but at least you'll know it'll bolt right up, and be completely safe to use. I'd never put any of my passenger's (or my own) life in danger just to spare a few bucks. Do it right and get a marine engine.

Re: 7.4 Engine Swap
 

One of the biggest things I found with the later model (gen 5/6) engines is the electronics. When comparing them side by side, you notice the subtle things that the car motors don't have,
Nor have bosses to install them.

If you have an old school carb/distributor motor (no knock sensors) their basically the same, except brass parts.

Re: 7.4 Engine Swap
 

I am pretty sure the cams are different.
Shabah has a point. The electronics of the open compartment auto world are not ideal for the closed compartment marine world. Fuel vapors an sparks an all...

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Re: 7.4 Engine Swap
 

What does that have to do with replacing a cracked block? Am I missing something? Take the engine out, replace the block, put it in and bolt everything back up to it. As an automotive engine machinist, I don't see the mystery here. A person doesn't keep wiring from a car and transfer it to a boat or vice versa. You replace the hard parts, and use the rest over.

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Re: 7.4 Engine Swap
 

I was out of line, I apologize. Key words being "interchangeable" and "block" while I have the thread title "engine swap" going on upstairs. It won't happen again...

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Re: 7.4 Engine Swap
 

Im not a Dr. but it seems like a legit question...

Re: 7.4 Engine Swap
 

This topic is debated on every major boat forum site, and the opinion is about 50/50 every single time.

The decision is entirely yours, but this may be worth a read. This is directly from Performance Product Technologies, one of the most reputable marine engine part retailers in the country.

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Question: Is There Really Any Difference Between a Marine Engine vs. Automotive?

Response: Contrary to what many people claim, there truly are several differences between the automotive and marine engines. These differences prevent automotive products from performing as well as the intended Marine Engine. Many people attempt to save money by utilizing an automotive engine rather than marine, however in our experience these situations rarely save money in the end. Be very careful with companies who claim to offer engines not being Marine Grade, but still being the same, or compliant, or some other fancy terminology. In the end the fact still remains that you get what you pay for.

The freeze plugs are of a corrosion inhibiting material.
The head gaskets also utilize corrosion resistant construction.
The valve guides utilize corrosion resistant construction.
The water pumps are intended for a marine operating environment (seals and bearings).
The camshaft is designed to marine duty requirements as needed to move a boat versus a car.
The overall duty cycle of a marine engine is very different than that of an automotive application. When was the last time your thought of running your car at full throttle for a sustained period of time?
- See more at: The difference between Automotive and Marine Engines | Performance Product Technologies
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Re: 7.4 Engine Swap
 

Nice Chris!:wink_thumbup:

Re: 7.4 Engine Swap
 

The problems ive seen are bosses for sensors either not there or not drilled and taped. The drilled the taped issue would be no problem to remedy, the missing boss is another.

Re: 7.4 Engine Swap
 

That's funny. Corrosion inhibiting material lol.

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Re: 7.4 Engine Swap
 

basically BRASS everything.

Re: 7.4 Engine Swap
 

I'm sure glad to have the peace of mind knowing my valve guides won't rust if I sink my boat in the lake. :D

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Re: 7.4 Engine Swap
 

Me too

Re: 7.4 Engine Swap
 

Has to do with moisture , not sinking............but hey...........I ain't no machinist either!:rolleyes:

Re: 7.4 Engine Swap
 

I figured the only way you'd get that much moisture in a valve guide is if you either sank the boat, or filled the crankcase with water instead of oil. I always get a kick out of these companies scaring people into spending more money. I wonder if the engines they sell are made of corrosion inhibiting cast iron and aluminum. :D To each their own.

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Re: 7.4 Engine Swap
 

A few years ago, I helped swap a cracked 350 with a block from a truck. Only difference we could tell were extra holes in the one from the truck. Plugged the holes, painted it gloss black and never looked back. The boat still runs great.

Re: 7.4 Engine Swap
 

like I said, if your engine is one of the basic carb models with no additional electronics, their 99% identical.

Re: 7.4 Engine Swap
 

I appreciate all the replies, theyre informative and entertaining haha...Ive heard pretty much the same from talkin to people is the cams are different, an automotive motor doesn't come stock with the low type torque cam of a boat plu the obvious switch to brass freeze plugs...a little history, I bought this boat at an auction (mistake 1) the fella running the auction assured me all it needed was upholstery (mistake 2) so I bought it (mistake 3) and brought it home only to find a lot of water in the oil pan, rusty spark plugs, and cracked water jackets (I didnt have time to inspect boat before auctions end) so I have a boat that I am leaning toward parting out due to the fact that it has sat in the blistering tx sun for atleast 6 yrs, I had a brain fart for a moment when I saw a cheap mark v 454 out of truck on craigslist, thinking of swapping. the outdrive and electronics appear to be good, I have the cylinders soaking in marvel mystery oil to see if I can get her to turn over...thanks again for all the replies