mercruiser 5.7l repower

[4nryde]

I have recently purchased a project boat and am looking for replacement engine options. Boat is a 1993 Malibu echelon with a mercruiser 350 magnum tournament ski motor. What will drop in relatively easy? I believe the motor in my boat is really similar to an 87-96 GM 350. I can get a great deal on a rebuilt 74 350 truck engine, any reason why that wouldn't work? What would need to be replaced to drop it in?

 

[edsmax]

Re: mercruiser 5.7l repower

Your best bet is two options: 1. buy a replacement MARINE 5.7 long block (Michigan Motorz, Jasper, etc) and transfer all of your components or better yet 2: buy a complete turn key carb motor with everything on it brand new and just drop it in. You will really want something with the Vortec heads. Dont even bother with the old truck motor. For around $6k you can get a Mercruiser 357 MAG 4V with 325hp. I just put one in my boat and it is great.

 

[Scott Danforth]

Re: mercruiser 5.7l repower

What is wrong with the motor in the boat now? you do NOT want to grab a '74 motor. you will want to stay with your 87-95 generation, however I recommend 90-95 to make sure you get another roller cam motor.

The block and heads are the same as trucks. Marine engines use brass core plugs, and composite head gaskets.

Depending on where you are located, you should be able to get your existing engine remanufactured for under $2k

 

[RogersJetboat454]

Re: mercruiser 5.7l repower

I can get a great deal on a rebuilt 74 350 truck engine, any reason why that wouldn't work? What would need to be replaced to drop it in?

Major differences between the '74 and your '93 is the flywheel used, and the intake manifold.

'74 uses a 2 piece rear main seal, which has a different crank bolt pattern for the flywheel then your '93. You would need to match a 2 piece flywheel to type of starter the block accommodates, and you would need a new coupler. The intake manifold is different in that the center 4 bolts on the intake are at a different angle then pre '87 engines (before center bolt valve covers). You would need to find an intake that matches the older style heads. The '74 has a port side dipstick, so you would need a pre 1980 oil pan if the engine doesn't come with one.

The core plugs should be changed to brass if they haven't been, and the head gaskets should be marine grade.

For easier adaptation, you would be better off finding a '87 or little later truck engine. Change the core plugs to brass, and the head gaskets. The rest should readily bolt on from your engine.

Mechanically a "marine" engine is no different then a truck engine. The major differences are the core plugs, gaskets, fuel system, and electrical system. Block, heads, crank, rods, pistons are the same. Cam's are pretty close.

 

[Bondo]

Re: mercruiser 5.7l repower

Major differences between the '74 and your '93 is the flywheel used, and the intake manifold.

'74 uses a 2 piece rear main seal, which has a different crank bolt pattern for the flywheel then your '93. You would need to match a 2 piece flywheel to type of starter the block accommodates, and you would need a new coupler. The intake manifold is different in that the center 4 bolts on the intake are at a different angle then pre '87 engines (before center bolt valve covers). You would need to find an intake that matches the older style heads. The '74 has a port side dipstick, so you would need a pre 1980 oil pan if the engine doesn't come with one.

The core plugs should be changed to brass if they haven't been, and the head gaskets should be marine grade.

For easier adaptation, you would be better off finding a '87 or little later truck engine. Change the core plugs to brass, and the head gaskets. The rest should readily bolt on from your engine.

Mechanically a "marine" engine is no different then a truck engine. The major differences are the core plugs, gaskets, fuel system, and electrical system. Block, heads, crank, rods, pistons are the same. Cam's are pretty close.

Ayuh,.... Agreed,... A cheap motor, that'll double in price to adapt....

Either stick with the '87/ 95 vintage, or jump up to Vortec heads with the '96, 'n up motors...

 

[4nryde]

Re: mercruiser 5.7l repower

The current motor has a crack in each side of the block. The 74 motor is appealing for 2 reasons, it is freshly rebuilt, and it is cheap. 1/4 the cost of the cheapest reman marine motor I can find. The 74 motor is complete from intake to oil pan, and has the flywheel installed. How much will it cost to replace the coupler? I cant justify spending as much on a crate motor as I have for the whole boat with trailer.

 

[Bondo]

Re: mercruiser 5.7l repower

I have recently purchased a project boat and am looking for replacement engine options.

The current motor has a crack in each side of the block. The 74 motor is appealing for 2 reasons, it is freshly rebuilt, and it is cheap. 1/4 the cost of the cheapest reman marine motor I can find. The 74 motor is complete from intake to oil pan, and has the flywheel installed. How much will it cost to replace the coupler? I cant justify spending as much on a crate motor as I have for the whole boat with trailer.

Ayuh,.... Are ya sayin' ya bought a junk boat, with a bad motor, 'n didn't figure in the cost of the proper replacement motor,..??

As noted above, repeatedly, ya Don't want the '74 motor...

 

[TilliamWe]

Re: mercruiser 5.7l repower

... rebuilt 74 350 truck engine...

Probably the WORST small block Chevy to start with. Engines from 72 to about 82 were ANEMIC at best from the factory. (seriously, 150 horsepower!) So to what specs was it rebuilt? Unless he put good heads and a good cam in it, it will be a DOG. Especially in a Ski boat. Which needs LOTS o'torque. And if he put a high lift/long duration cam in it, that's BAD for water cooled exhaust manifolds.

DO what the folks are advising. Get either an engine from 87-95, that's just like yours. Or pony up and get something from 96 and up with Vortec heads. You won't be sorry.

 

[4nryde]

Re: mercruiser 5.7l repower

Didnt know the motor was junk until I got it home and started to deal with the known issues. I expected to rebuild the motor, but then found out the previous owner covered some cracks in block with JB Weld. Needless to say, I didnt expect this. Compression test came back normal, but leak down test was not performed. I removed the hoses from the exhaust manifolds and pressurized the cooling system in block and intake. It did not seem to leak.

What would it take to bolt in a newer vortec engine? What would I need to replace then? I am looking at long blocks, not turn key crate motors to cut down on costs.

The 74 motor was bored .30 over with a stockish cam installed. If it really is a horrible option, I will forget about it. Just seemed like a really good deal.

 

[Scott Danforth]

Re: mercruiser 5.7l repower

a vortec motor will need a different intake for the vortec heads.

I myself would call a local machine shop and build a motor. A nice 383 with vortec heads.

 

[4nryde]

Re: mercruiser 5.7l repower

So new intake.....will everything else bolt up? My motor is carb'd, so will this create any extra problems?

 

[Scott Danforth]

Re: mercruiser 5.7l repower

the vortec heads have different intake shapes and combustion shapes than your current motor, hence the need for a different intake.

carb, distributor, starter, alternator, exhaust, etc. will all bolt up just fine.

 

[4nryde]

Re: mercruiser 5.7l repower

Just making sure I understand. Anything 87 and up should work, but if I choose a newer motor (95+) I will need an intake?

 

[Scott Danforth]

Re: mercruiser 5.7l repower

vortec heads were introduced in 1996

 

[4nryde]

Re: mercruiser 5.7l repower

Running a carb on one of these newer vortec engines isnt a problem? What about the thunderbolt iv distributor on my current motor?

 

[Bondo]

Re: mercruiser 5.7l repower

Running a carb on one of these newer vortec engines isnt a problem? What about the thunderbolt iv distributor on my current motor?

Ayuh,.... No problem with either...

 

[Glaspar_Fan]

Re: mercruiser 5.7l repower

I just got a new long block from Michigan Motorz. Haven't installed it yet, so no comment on quality, but the service and delivery so far have been good. As others pointed out, the intake is entirely different. From what I can tell, your timing cover and damper will also be different, so you might want to check on those when you get serious about an order. There are also two different flex plates based on how your starter is mounted.

Something I ran into is that there isn't much of a selection for cast iron Vortec style intake manifolds and the ones that are out there are expensive. Plenty of choices for aluminum, but for a raw salt water cooled engine, I chose cast iron. The original intake on the boat mostly seemed OK, but it appeared that there may have been some leaking around the water passage ports. And there was a quite a surprisingly large corrosion pit at one of the back corners where the manifold is simply blocking off the water passages. By large, maybe 1/2" long and 3/16" deep. That was when I got serious about ordering the cast iron intake. The water passages up to the thermostat housing looked good though, so maybe Al would have worked.

John

 

[Scott Danforth]

Re: mercruiser 5.7l repower

they make aluminum intakes with bronze inserts where the water is.

 

[4nryde]

Re: mercruiser 5.7l repower

Aluminum is OK for freshwater?

 

[RogersJetboat454]

Re: mercruiser 5.7l repower

Aluminum is OK for freshwater?

Yes, aluminum should do OK in freshwater. Not going to have the same longevity as iron, so it should be checked out every few years, but it's not going to dissolve like it would if you were raw water cooled with salt water.