[usafdaytonan]

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

[husker_fan]

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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[doaclnr]

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...

[ShabahZ280]

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.

[Oregondunes]

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.

[Motoxxx43]

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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[husker_fan]

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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[Motoxxx43]

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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[doaclnr]

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

[ShabahZ280]

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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