Mercruiser re-power. What motors and outdrives to look for and to avoid?

[pckeen]

I've agreed to buy a 25' Aluminum Cuddy Cabin / Cabin Cruiser (a 1974 Starcraft Chieftain), rated for up to 280hp. The project will be a complete restoration. The boat is supposed to have a 160hp Mercruiser (GM inline six) in it. I suspect it's a Mercruiser 165. I'm told the motor runs well, but the exhaust manifold is cracked, so I'm assuming the block is cracked to.

I want to have a reliable motor in the boat, but I know next to nothing about mercruisers. For ease of restoration, I want to repower with a Mercruiser, as the keyhole will fit the outdrive. I would consider anything from a brand new motor, to an older motor with low hours on it that is known to be reliable. While I would buy new if necessary, my last re-power was a one year old 90 HP Yamaha from a wrecked one year old boat, with an all new steering system and controls.

I'm beginning the hunt now for a replacement motor. I'll consider anything from new, to a local rebuild, to a remanufactured motor, to recent model motor from a wrecked boat, to an old model from a wrecked boat.

So what Mercruisers should I look for, and what should I avoid?

Other than hearing/seeing a motor run, what should I check for in a used motor?

 

[achris]

The old inline 6 is now a very old engine (finished with Mercuiser in 1981). There are still many of them running around happily, but if I was doing this sort of job, I'd be looking for a donor boat with either a later model V6 or V8. I would definitely be looking at nothing earlier than 1991 (that way you are into the current stuff, Gen II). As the boat is rated to 280hp, I would be looking to power as close as I could to that rating, that means a 350cu in V8, the Mercruiser 5.7LX. I wouldn't both with new as there are plenty of donor boats out there, and even if the engine itself is a bit dodgy, there are PLENTY of 350s in trucks. Just replace the core plugs and head gaskets and you have a marine long motor. If you are looking for a good engine, check compressions and run the engine and look for external water leaks (freeze cracking) and for milky oil (also freeze cracking, but on the inside of the block)....

Good luck.

Chris.....

BTW, if you (or anyone else) is thinking a smaller engine will use less fuel. Wrong. Infact a smaller engine will use MORE fuel for the same boat speed, as it's having to work harder. A few examples. My boat had a 165hp (in-line 6). Since having the 4.3MPI (220hp), for the same boat speed I use about 20% less fuel. My car. originally had a 4.2L 6cylinder diesel, now has a 6.5l V8 diesel, uses about 25% less fuel.... My mother has a 2.4l Mazda. uses less fuel than her partners' 2.0l Nissan on the same trip. My brothers' boat, had a 65hp, he replaced with a 90. Rang me a few days later to 'complain' that it was using way less fuel.

 

[NHGuy]

Exactly, on the fuel use. Except for the cowboys who run full bore.
On my last boat I upgraded the cam & lifters. It improved mid range, hole shot, top end and fuel economy.

 

[achris]

...Except for the cowboys who run full bore.....

Oops! I be one of those cowboys :facepalm: but it is fun.

 

[Scott Danforth]

Motors / drives to avoid:
Any of the 3.7 liter combinations
Any Ford powered version

Motor combinations recommended:
An GM powered Mercruiser combo from the last 18 years.

If your key is reliability, they are all only as reliable as the maintenance that goes in them.

As for fuel economy, it's a boat.

My recommended packages would be a 5.7 liter/alpha combination from 1997 or later, 5.7 bravo 3 package from 97 or later, or a 5.0 efi/Bravo 3 package.

 

[Scott Danforth]

Oops! I be one of those cowboys :facepalm: but it is fun.

I also have only 2 positions of the throttle

 

[redmen62]

Heck, if it were me I'd rebuild and put that 165 back in! I'm a old boat guy and like to keep them original. I put my 106 back in, and it rips pretty good. Merc may ave stopped using that engine in 81, but GM used it until 2001 in some areas.

With the boat being aluminum, it's not going to weigh a whole lot at all... with a 5.7 you might find yourself having too much power and you'd have to do your homework on prop choices to avoid cavitating when you try to plane out. I'd recommend a a 4.3v6 with an alpha 1 gen 2 drive.

However, with any of these recommendations, you're going going to be able to use any of the current transom/gimbal assembly. They changed from the pre-alpha models (R, MR, ect.) and again with the gen 2 in 1991

 

[NHGuy]

If I went full on all the time I'd be in divorce court and my dog would disown me too. But it's good to have it available!

 

[pckeen]

Heck, if it were me I'd rebuild and put that 165 back in! I'm a old boat guy and like to keep them original. I put my 106 back in, and it rips pretty good. Merc may ave stopped using that engine in 81, but GM used it until 2001 in some areas.

With the boat being aluminum, it's not going to weigh a whole lot at all... with a 5.7 you might find yourself having too much power and you'd have to do your homework on prop choices to avoid cavitating when you try to plane out. I'd recommend a a 4.3v6 with an alpha 1 gen 2 drive.

However, with any of these recommendations, you're going going to be able to use any of the current transom/gimbal assembly. They changed from the pre-alpha models (R, MR, ect.) and again with the gen 2 in 1991

Assuming I use a newer motor, I'll go the whole hog and use a new(er) Alpha or Bravo outdrive.

 

[achris]

Assuming I use a newer motor, I'll go the whole hog and use a new(er) Alpha or Bravo outdrive.

:thumb:

BTW. Don't be worried about "too much power". There is no law that says you have to use all you have. You can always back off, but never increase when you are already at full noise!

And there is zero weight difference between the 5 litre V8 and the 5.7 litre V8.... Just saying (and I think most here agree, the 5.7 is a far better engine)...

Chris........

 

[pckeen]

So here is a question. If I'm looking at donor boats or engines plus outdrive that someone has already removed, what should I look for? About all I know is to look for obvious leaks, visual condition of the motor (looking for no rust, cracks, condition of wiring and hoses), water in the oil, number of hours, and to run it if at all possible. Are there any other tests/checks I can do?

 

[achris]

Even if the engine is out of the boat you should see it run. For a boat engine, setting up to run 'on a stand' is extremely simple. Then you can do your compression checks.

For the drive all you can really do is check the drive oil, and turn it and see how it feels. And unless you have experience with drives, it's hard to know what feels right. Transom housing, look for obvious signs of corrosion, and if water has been in the bellows. Check the shift cable condition (although that's easy enough to replace) and be sure it's all there.

 

[pckeen]

Will any 1991 or later motor work with an Alpha Gen 1 or Gen 2 or Bravo outdrive, or are there other components I would need to change?

 

[harleyman1975]

Lower part of the outdrive is same but upper part, bellhousing and transom mount can be different (gear ratios, distances, ect...) and should be for that particular motor. the stuff on your transom will only work with a straight 6 due to imput shaft length. Motor mounts will also have to be remanufactured if you switch to anything other than a straight 6.

 

[Bondo]

Will any 1991 or later motor work with an Alpha Gen 1 or Gen 2 or Bravo outdrive, or are there other components I would need to change?

Ayuh,..... Let's assume, the hull is Bare,.... No transom assembly, no trim pump, Nothin' Mercruiser but the keyhole in it,.....

The keyhole has grown slightly over the years,.....
The upper, 'n mid-bolts changed position slightly in the early '80s, 'n in '91 the 2 top bolts were added,...
The Alpha, Gen.II is exactly the same as the Bravo keyhole, now pretty much the industry standard,....

Find a donor boat, with the driveline ya want, at whatever yer budget is,.....
'round here, $3500. to 5 Grand will get ya into an '80s 5.7l/ Alpha 1,.....
For under $10,000. ya can get into a fairly new wrecked hull,...
The sky is the limit, but ya gotta dig to find 'em,....
Junk the donor, 'n ya got all the tiny expensive pieces it takes to make a marine driveline Run,...
A few gasket sets, 'n yer Boatin',....

Dates to consider, Alpha 1 started 'bout '83,....

Alpha, Gen.II started in '91,....

Bravo was intro'ed in, I believe '89,....
Many improvements over the years, no doubt newer is better, but a Bravo is Great, though marginally big for yer project,....
A few pounds heavier than an Alpha driveline,....

Tryin' to piece together a driveline leads to all this, will this work with that kinda questions, 'n usually expensive answers,....
A donor barge sounds expensive at 1st, but the bottom line it's usually the cheap way out,....

 

[pckeen]

That's excellent Bondo - then I guess what I'm looking for is a post 1991 donor boat, with an Alpha II outdrive....

 

[Bondo]

That's excellent Bondo - then I guess what I'm looking for is a post 1991 donor boat, with an Alpha II outdrive....

Ayuh,..... If ya go 5 years newer, ya get to the Vortec heads used on Chevy motors,....

Basically, a free extra 20 horsepower,....

Vortec heads came out in '96, on the 4.3ls, 5.0ls, 'n the 5.7ls,........

 

[HT32BSX115]

I've agreed to buy a 25' Aluminum Cuddy Cabin / Cabin Cruiser (a 1974 Starcraft Chieftain), rated for up to 280hp.

Howdy,

Several years ago, I removed the OMC 460 and King Cobra from my Four Winns 211 (21ft) boat with the same idea. Replace with a similarly sized Mercruiser or Volvo engine and drive.

I found a 2004 model year 5.7L V-8 + Bravo I package (closed-cooled, 300hp EFI, 400hrs) that, while somewhat "smaller" and lighter than my 460, it was rated at approx the same (prop-shaft) power as the original 460 + King Kobra.

I was in the process of negotiating for the 5.7/Bravo I when I found a 1997 7.4L(122hrs) Bravo III package for a couple thousand less that was fairly close by, so I bought it.

I was not all that enamored with the idea of going from a single prop drive to a "Duo" prop. (mainly because I thought it would be slower and thought a dual contra-rotating prop was more suited for a cruiser......the 211 is a sort of a go-fast boat)

Although I was wrong about the Bravo III it didn't slow me down much at all, but more importantly, it took a boat that was a real dog out of the hole and made it ROCKET out of the hole! I also noticed that I actually do burn less fuel than I did with the 460. The 454 is similar to the 460 in many ways. THe dual contra-rotating props will reduce slip quite a bit which does make the entire thing more efficient.

I think a Bravo III mated to a 5.7L V-8 would be perfect for your 25ft cruiser and I also think you would be amazed at the performance you would get with it.

It does cost more for a Bravo III, but it's certainly worth considering.

Post some pictures!

Regards,


Rick

 

[pckeen]

As for pics, here is what I am repowering. The repower is part of an overall restoration.. I'm trying to find a donor boat at the moment with a package that puts out between 220 and 280hp. Most likely candidate will be a 5.0 liter or 5.7. With Bondo's advice, I'm looking for a mid-late 90s boat.

 

[HT32BSX115]

As for pics, here is what I am repowering. The repower is part of an overall restoration.. I'm trying to find a donor boat at the moment with a package that puts out between 220 and 280hp. Most likely candidate will be a 5.0 liter or 5.7. With Bondo's advice, I'm looking for a mid-late 90s boat.

Nice looking boat!

The Bravo III drive is used behind the 4.3L V-6, 5.0L and 5.7L V-8s (and all the other larger V-8's)

A Bravo III + any of the above engines would be a perfect match!