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

[pckeen]

OK - I've located a Mercruiser Scorpion 350 with a velvet drive and low hours, priced under $6k Canadian. I know nothing of these motors. Assuming its in good mechanical condition, is this a decent buy? I see that the Scorpion isn't being produced any more, but I could find very little on it in my recent searches. Anyone know anything about these motors?

 

[Bondo]

Ayuh,.... A full in-board ain't gonna help ya, ya need an I/O driveline,......

 

[HT32BSX115]

OK - I've located a Mercruiser Scorpion 350 with a velvet drive

Yeah A Velvet (transmission)drive is used with inboard boats. To switch to an inboard setup, you usually move the engine to a "MID" position, which severely changes the center of gravity of a boat that was originally designed for a stern drive.

With a stern drive (and an outboard), the engine is very close to the stern, and with the drive literally hanging of the back, the boat has to be designed to such that the center of gravity is right with all that weight in the back. The angle of thrust (down with an inboard) helps, but it has to be taken into consideration. PLUS, since the angle of thrust is down (and fixed) it's FAR less efficient when compared to an adjustable thrust-angle stern drive or outboard

A boat originally designed to run properly with a stern drive or outboard will have CG problems if fitted with a mid-engine/Velvet drive and inboard setup....It wouldn't be impossible, it just wouldn't be worth it.

 

[thumpar]

I think the 5.7l would be the best choice. You don't need a Bravo unless you really want one. The Alpha can handle the power. Like said get a post 1996 engine for the Vortec heads. A 4 barrel carb will also get you some extra power.

 

[HT32BSX115]

You don't need a Bravo unless you really want one.

I wouldn't do a Bravo either, unless it was going to be a Bravo III.....

...But a Bravo III would be a HUGE performance increase over an Alpha (or a Bravo I) using the same engine.

 

[pckeen]

Ok, so nay on the Velvet Drive and associated power plant. I've been offered a boat with a low hours 98 4.3 Merc 190hp, for CN$4k, but I'm thinking it will be underpowered.

In chatting with the dealer, he advised that if moving from the straight six I have now, to a V6 or V8, the motor mounts may need to be moved. He seemed to think this may be a problem, requiring some welding of new mounts. What is the story with this. Shoudl I expect to have to weld some new mounts?

 

[HT32BSX115]

Ok, so nay on the Velvet Drive and associated power plant. I've been offered a boat with a low hours 98 4.3 Merc 190hp, for CN$4k, but I'm thinking it will be underpowered.

In chatting with the dealer, he advised that if moving from the straight six I have now, to a V6 or V8, the motor mounts may need to be moved. He seemed to think this may be a problem, requiring some welding of new mounts. What is the story with this. Shoudl I expect to have to weld some new mounts?

A 4.3L V-6 will perform a tad better than the original 250 cu-in inline did. (190hp Vs 165hp but you might not notice a huge difference.)
[If it were me, I would hold out for at least a 5.0L V-8 preferably a 5.7L]


Regardless, you will need to install side engine mounts unless the boat has mount points.

Many boats were offered with inline and V-type engines, so they might be there now. If not, you'll need to get a welding shop to fab them and weld in place. You would ideally do this after the engine has been mounted to the transom plate and is supported in front so you can locate the proper location.

Here's an installation manual you can read through.
http://www.boatfix.com/merc/install/gas/86017211.pdf

 

[Bondo]

If not, you'll need to get a welding shop to fab them and weld in place. You would ideally do this after the engine has been mounted to the transom plate and is supported in front so you can locate the proper location.

Ayuh,..... When I went from a 2.5l to a 4.3l motor, I bent motor mount plates outa .090 aluminum sheet, 'n pop-riveted 'em into place,....

That was 'bout 2000 hours, 'n nearly 20 years ago,.....

 

[TyeeMan]

Just a thought here you might be interested in. I just purchased a 97 Lund 1950 Tyee Magnum that has a rebuilt 5.7 in it. I've been away from Mercruisers for a few years so I'm re familiarizing myself with Mercs. Anyway I really wanted to know who did the rebuild. After doing some home work I found out that it was reconditioned by Merc, but it gets better. They call it a Mercury Re-Manufacturing Plus Series engine. So it's bored .040" over which makes it 357 cubic inches or 5.8 liters. They do re-use some usable parts like rods, cams, cranks and some other parts only if they are in spec. They do install new pistons, new stainless steel valves, heavy duty valve springs, and a high flow oil pump.
Then they go and strap on brand new exhaust manifolds and risers, new intake, new 750cfm 4 barrel carb, new fuel pump, water pump, power steering pump, alternator, and the latest and greatest Merc Thunderbolt ignition with knock control. It's basically a turn key system, drop it in the boat put some gas and 12 volts to it and go.
Oh, they bumped the ponies up to 275hp.

If you type in your browser Mercury Re-Manufacturing 357 Alph 4V it will take you to the Merc site where they have a brochure and videos on the Plus series engines

Anyway, just thought I'd throw that out there as a way you could have basically a brand new power unit and save yourself some time looking for engines, manifolds and all the rest of it.

Unfortunately they are a little pricey at about 8K, but think of the piece of mind with all that nice new stuff in the back of the boat.

 

[HT32BSX115]

Ayuh,..... When I went from a 2.5l to a 4.3l motor, I bent motor mount plates outa .090 aluminum sheet, 'n pop-riveted 'em into place,....

That was 'bout 2000 hours, 'n nearly 20 years ago,.....

you know me..........I want to over-build everything!!!!

 

[pckeen]

Just a thought here you might be interested in. I just purchased a 97 Lund 1950 Tyee Magnum that has a rebuilt 5.7 in it. I've been away from Mercruisers for a few years so I'm re familiarizing myself with Mercs. Anyway I really wanted to know who did the rebuild. After doing some home work I found out that it was reconditioned by Merc, but it gets better. They call it a Mercury Re-Manufacturing Plus Series engine. So it's bored .040" over which makes it 357 cubic inches or 5.8 liters. They do re-use some usable parts like rods, cams, cranks and some other parts only if they are in spec. They do install new pistons, new stainless steel valves, heavy duty valve springs, and a high flow oil pump.
Then they go and strap on brand new exhaust manifolds and risers, new intake, new 750cfm 4 barrel carb, new fuel pump, water pump, power steering pump, alternator, and the latest and greatest Merc Thunderbolt ignition with knock control. It's basically a turn key system, drop it in the boat put some gas and 12 volts to it and go.
Oh, they bumped the ponies up to 275hp.

If you type in your browser Mercury Re-Manufacturing 357 Alph 4V it will take you to the Merc site where they have a brochure and videos on the Plus series engines

Anyway, just thought I'd throw that out there as a way you could have basically a brand new power unit and save yourself some time looking for engines, manifolds and all the rest of it.

Unfortunately they are a little pricey at about 8K, but think of the piece of mind with all that nice new stuff in the back of the boat.

I looked into those a couple of weeks back. These are essentially new engines - but with a matching new lower unit, I'd be looking at 12-14k, including the install. If I do that, I'll be financing. I'm hoping to find something for under 5k, as then I'll be able to buy cash.

 

[HT32BSX115]

In 2006, I paid $5000 for a complete fanbelt-to->prop 1997 454/Bravo III with 120hrs since new + all the controls, harness, gages etc.

There are deals out there.......you just have to be patient.

 

[pckeen]

I have a line on a complete motor and outdrive - a1987 V8 5.7 260hp mercuriser, with a SE106 outdrive, from someone I trust. Details on it are it has approximately 400 hours, running, with good compression (122-130 on all 8 cylinders). In terms of issues, the seller reports that there was some water coming into the trim oil, the port side of the block was getting hotter than the starboard side (so a thermostat issue was suspected), and some minor belt squealing issues that can likely be solved with tightening some pulleys and replacing belts.

So questions - how tough is it to rebuild the trim unit, how hard is it to find parts for this model and year of IO, and are there any danger signs that you see?

 

[thumpar]

That is a good power plant. The trim problem is probably a seal in the rams or somewhere in the lines. It is normal for the engine to run hotter on one side. If you can keep your hand on it it is fine. The compression is not fantastic but not terrible. The belt squealing could be caused by rusted pulleys.

 

[HT32BSX115]

I have a line on a complete motor and outdrive - a1987 V8 5.7 260hp mercuriser, with a SE106 outdrive, from someone I trust. Details on it are it has approximately 400 hours, running, with good compression (122-130 on all 8 cylinders). In terms of issues, the seller reports that there was some water coming into the trim oil, the port side of the block was getting hotter than the starboard side (so a thermostat issue was suspected), and some minor belt squealing issues that can likely be solved with tightening some pulleys and replacing belts.

So questions - how tough is it to rebuild the trim unit, how hard is it to find parts for this model and year of IO, and are there any danger signs that you see?

Does the drive also have 400 hrs on it or is the 400 hrs on the engine?
That sounds like a fairly good deal to me too. I would be somewhat concerned about the rather low compression but if the drive is in good condition you can fix most of the other stuff fairly easy.

 

[pckeen]

Drive is an aftermarket, so I assume less. The 400 hours is on the engine.

 

[HT32BSX115]

Drive is an aftermarket, so I assume less. The 400 hours is on the engine.

Nothing wrong with an SEI drive, but they're quite a bit cheaper than a Mercruiser drive. So the total value of the package would be less than if it were all MCM

 

[pckeen]

So a bit of a twist. I've got a line on a donor boat with a 5.7 in it. However....

The boat I am repowering has a maximum HP of 280hp (based on the best available information I have, plus doing the USCG's calculation). However, when the boat was originally sold, the 350hp wasn't an available option - to get the 280hp, you had to purchase twin 140s. The single engines available were the 165, 470, 198 and 228 if you used a Mercruiser. An OMC engine option - the 240 was available..

Do I understand correctly that the highest HP motor available in a single motor was the 240hp 305? If so, would I be overpowering with a 5.7?

 

[HT32BSX115]

So a bit of a twist. I've got a line on a donor boat with a 5.7 in it. However....

The boat I am repowering has a maximum HP of 280hp (based on the best available information I have, plus doing the USCG's calculation). However, when the boat was originally sold, the 350hp wasn't an available option - to get the 280hp, you had to purchase twin 140s. The single engines available were the 165, 470, 198 and 228 if you used a Mercruiser. An OMC engine option - the 240 was available..

Do I understand correctly that the highest HP motor available in a single motor was the 240hp 305? If so, would I be overpowering with a 5.7?

You're not going to "over-power" that boat with a 5.7 in it unless it's a bored stroker engine! Most Mercruiser 5.7 carbed engines are rated at less than 300HP.

 

[thumpar]

Normally a 5.7l is 260hp unless it is a MAG and then it would be 300hp.