I have a friend who has a mercruiser 5.7 with a cracked block. It is a GM 350 engine.

Finding an engine or short block has been a problem so we are toying with the idea of building GM 4 bolt main truck block with the good parts from his engine.

I know that for most RV/Boat engines they used beefier heads and occasionally beefier blocks.

Would a 4bolt main block from a truck do the job or are there other issues?

Thanks

How hard does he run his boat? Light loads? Heavy loads? Just cruising? Big heavy boat? Small, light boat? A non-marine block can work in some situations.

And be sure the block is all that is cracked assuming that it froze and busted. There could be other damage, too.

In the '78-'80 era, we ran a 130-MPH tunnel-hull with a SBC automotive race motor.
No issues, though we'd warm it up before hammer time; freshened it yearly but it held up well.

He should do what I did when, long story short, my '5.0 Mercruiser engine had an issue in my 22' Sea Ray. I tried to have my local performance engine shop do some machine work on it and that wasn't going to happen until the boating season was over. He said "Mike I was just down at Summit Racing and sitting there for $2300 was a BRAND NEW GM Goodwrench 5.7/350 crate motor and for a few more bucks for a Melling new camshaft and some brass freeze plugs you will have a NEW motor. Plus there no telling what you get when you buy a used block or motor especially if it's out of another old boat. Go to Summit and buy a new GM Goodwrench 350 crate motor and change the cam and freeze plugs and use the boat intake manifold, fuel pump (I bought a new marine fuel pump) and use all of the other boat specific components. I picked up 65 hp too going to the 5.7.

Mike

I checked Summit and no GM Goodwrench but ATK But Jeg's list this https://www.jegs.com/i/JEGS/059/7353/10002/-1

This is the engine I have in my boat now:

Thank you all for the replies.

It is about a 15 to 20 foot boat similar to a ski style boat. No cabin or fishing rigging. Sorry I am not that much on the correct boat jargon. No idea how he uses it. A guy was trying to sell him a short block with rust in the cylinders for $1500 when I said no let's look at other choices.

I will definitely look at a crate motor.

The heads were reworked about a season before the cracked block was found.

It had a crack in the block and one exhaust manifold but aside from that the boat specific parts are ok.

I was the Crownline factory local dealership for years. In my humble opinion, a 5.0 is just a little too small for most 22 footers. Might be okay in some models and in some applications, but in most cases like the 102" beam 225 Crownline, a 305 wasn't enough. But I have seen Crownline 225 Cuddies with 4 cylinders in them. I was shocked the first time I seen one going down the line and asked them what on earth they were thinking selling that combo. They were going to Germany where the boats just idle along in the canals. In that application, 140HP was enough.

I sold several 225 Crownlines with Merc's 502 Mag EFI. Lost a few camshafts and has to replace the engines. Typical GM big block crap. But when they had all 16 lobes on the cam, they were FUN!

And I ordered 6 182s with the OMC Cobra Ford 5.0 EFI. Basically the Mustang engine. I had to order 6 for Crownline to mess with the USCG certification. Those were fun little boats. After that initial batch, I always kept one or two V-8 182s on hand and I suggested that anyone wanting to load the 182 with friends and family or were going to pull skiers and toys to go with the V-8. With the right prop, they would come out of the hole hard enough that they felt like they bounced when the bow hit the water. And that V-8 was much, much smoother than that 4.3 V-6 GM. The 182 Crownline with the Cobra 5.0 EFI is hands down my favorite bow rider EVER!

And that Ford was far more durable than the big block shivvies. The only Fords I ever changed were due to freeze damage. I don't remember a single internal failure. Unlike the shivvies.