Blown Mercruiser 5.0 Alpha. Low hours. Replacement options

[keith]

Hi All,

I bought my 23 SF late last year and it didn't run great on the test drive. I bought it from my great uncle's best friend (who is very sick) and figured it needed a tune up. Cap, rotor and coil looked bad. 2007 5.0 alpha (carb) with a 2007 alpha one gen2 outdrive. 280 hours on the package. Rewired the boat and tuned it up and found out the compression was bad. 0 on two (opposite) cylinders, 50 on two, 150 on two and 170 on two. I have the option of using a long block and swapping the parts or going all new. I am concerned about the long block idea because I am afraid of what blew the engine so soon. Any advice on a new power plant for my boat?

5.0 mpi
5.7 mpi
5.0 carb
5.7 carb
or this new motor 4.5L https://www.mercurymarine.com/en/us/...specifications

Pretty unhappy with the whole situation but what can you do. I think since I have the opportunity to upgrade I may as well but wanted the opinion of the Seacraft squad.

Thanks

[FLexpat]

5.7
MPI vs carb is a debate that goes on forever - do what you are most comfortable with.
If you want to go fast look at a 383 stroker; same size & weight but more $ - although it is really on the upper limit for an Alpha drive.
Small block V8 has a lot more parts available than the 4.5 and although a 4.5 is an interesting idea (The 4.5 gets you ~130# weight savings), I would lean towards the 5.7 and not having to push the engine at all.
Lots of marine engine manufacturers (new and rebuilt) out there to choose from so you are not forced into a black motor unless you want it. I have had good luck with Marine Power but look around.

[pelican]

alpha drives are restricted to below 300hp

bravo drives,specifically the bravo I is allways the best choice

with all that:

odds are,the manifolds/risers caused your problem.test running something,and the rpms are not right,nor does the motor"seem right" always think the wost ! "tune ups" rarly cure anything - you need to find out why something isn't right


me,i do not like reman ! I also will not use a long block I like and use new,complete motors only - always the best choice !

my advice:

merc 5.7 MPI motor,new - pull out the old and drop in the new


call this one "experience"...

[Old'sCool]

The bright side; That's a lot less $$$$ than say a new Yam 300 for an outboard 23

[DoozleD]

I think i would go with a 5.7. parts are allover the place! one thing to keep in mind is the 5.0 and 5.7 outdrive gear ratios are different so if u go 350 you are going to have to get a 1.47 upper for you drive.

[keith]

Thanks for all of the great advice everyone.

I decided to have them pull the heads and take a look myself at the situation. If the cylinders look good I will go ahead with machining the heads and valve job and see what happens. If the cylinders look good I will have them change the manifolds too. I would rather have a new fuel injected engine in there. Hopefully I can delay that expense for a few years.
They are pulling the heads on Friday.

[FishStretcher]

Good luck! I am rather new to I/Os but I know I was warned about having sufficient height of the elbow in the riser in my 25. My local shop suggests a new flapper in the y pipe, too.

The extension to the riser is not that pricey for a raw water engine. They are a bit dear for a FWC engine.

Not sure if it is as big a deal on the 23 as the 25 as the engine likely isn't as low in the water.

[pelican]

Originally Posted by keith

Thanks for all of the great advice everyone.

I decided to have them pull the heads and take a look myself at the situation. If the cylinders look good I will go ahead with machining the heads and valve job and see what happens. If the cylinders look good I will have them change the manifolds too. I would rather have a new fuel injected engine in there. Hopefully I can delay that expense for a few years.
They are pulling the heads on Friday.

once manifolds are pulled off - it will be apparent if the manifolds/risers caused the problem.

if indeed the manifold/risers caused this condition - the motor was taking in sea water.water in the oil,it may or may not have been present,but,the motor was "burning" seawater,due to valve overlap ...

with all that:

a common problem often encountered,after having the cylinder heads rebuilt - a "valve job"
the motor will have an oil consumption problem.blow by,on the rings will cause this.the seawater in the cylinders causes wear on the rings - just inspecting the cylinders,will not pick this up...if water was in the oil,this causes a problem with the cam bearings,causing a low oil pressure situation ....


lots of "stuff" to all this huh ??

[keith]

Pulled the heads and there was rust on the two of the cylinder walls and the valves were toasted and mushroomed. Engine is gone. I am still waiting on prices for 5.7 mpi and 5.7 carb. He is recommending the Mercruiser reman units but doesn't know the availability or pricing yet.

[keith]

Is there a difference on the installation for swapping my carb (alpha) motor with an mpi 5.7? If they can't get it done in time I am debating on doing it myself at my friends shop. I don't want to get into anything too crazy though.
Is the harness the same?
Will the exhaust bolt up?
Do I have to change anything in the outdrive?
Is the fuel pump on the engine?
Is there a return line, which would mean tank modification?

Thanks