Time to chuck the 470

[teardropty]

I am at my wits end with a 1986 Mercruiser 3.7 170 aka 470. It is coupled to a Alpha 1 Gen 1 outdrive sitting in a 1986 Searay Seville CC 19'. I have a cracked exhaust manifold (cant seem to find a decent used one), low compression across all 4 cylinders (65psi) and a leaky oil pan. I am looking for any ideas about something I can swap into the boat that will be relatively less frustating than rebuilding the 470 and knowing it will crap out again sometime soon. And before someone suggests just scrapping/selling the boat, I can't. It belong to my dad and has too much sentimental attachment. The boat also needs some stringer/glass work so redoing the stringers and/or transom isn't out of the question if going to a V6 for example. I have researched the topic but mostly what I get is bits and pieces. Has anyone swapped in something?

 

[nola mike]

Nola Mike's 3.7/470 --> 4.3L swap thread

I'm sure that this will be a saga, so starting a new thread. Just picked up an '89 Glastron donor with a 4.3. I'm planning on refurbing the engine and adding a 4bbl carb and vortec heads. I'm going to start on the engine in a bit, and then swap it in the fall after the season. 1st question...

forums.iboats.com

Also, where are you located?

 

[Scott Danforth]

I would swap in an entire 5.7/A1G2 into the boat

 

[Bondo]

Ayuh,..... Welcome Aboard,.... Goin' with a 4.3l will allow use of yer current drive, as the ratio is right,.....

 

[Scott06]

Here is a 4.3 install drawing https://samerwebapp01apncus01.azure...phawithtwo-pieceexhaustmanifold_1996-2001.pdf

Here is a 5.7 drawing https://samerwebapp01apncus01.azure...41bb-90c9-f0958ee21906/57lalpha_1996-2001.pdf

biggest issue you will have to negotiate is the engine compartment width and length. Being inline may need to widen fir a V engine.

other big one will be the side motor mount stringers usually some built up blocks of wood glassed in.

theres a lot of other details but id start here. Bottom line if the boat has value to you it helps justify the effort and cost.

 

[QBhoy]

3.0 will drop straight in and easier. If it makes a difference to you. Depends on your needs and talent, if you want to go anything else.

 

[Scott06]

3.0 will drop straight in and easier. If it makes a difference to you. Depends on your needs and talent, if you want to go anything else.

Good point this would be a good option if a V required extensive rework to engine compartment/cowling.... only issue will be going down in power. If you just putz to a swimming spot or evening booze cruise prob doent matter if propped right

 

[QBhoy]

Good point this would be a good option if a V required extensive rework to engine compartment/cowling.... only issue will be going down in power. If you just putz to a swimming spot or evening booze cruise prob doent matter if propped right

Yeah. For sure. Scott, I got a bit of stick from some guys on here for it last time, but my very close friend (told this story loads previously) had a darragh 22ft boat with a 3.7 in her. Was a cruiser thing…all be it, a fairly light built one, but certainly heavier than most any 18/19ft open boat of the usual type. Long story short, he had issues with the original engine. Found out the previous owner did too. The usual issues of course. Mended them as best we could…new pump and head work etc etc. then that gave in too with the usual issue after these things give out. Ended up with another good but used 3.7 in her. Similar issues within a year or so. He wasn’t the type that wanted to mess with things like constantly tinkering with an engine, like these things need. So he just ended up putting a brand new 3.0 in her. Mated to the same pre alpha drive. Actually used the same 17” black max prop too. The 3.0 did just a fine job to be fair on it. There was a little lack in grunt to get on plane, compared to the old 3.7 (when it did work)…but if you hadn’t experienced the old engine, you’d not be complaining about the 3.0 and the job it did. As for the top speed…if you didn’t have a gps Speedo and monitoring it closely, you wouldn’t notice the difference top end. Was only about 1 or 2 mph slower. The boat seemed much lighter too. If he wanted to mess for perfection, he might have tried another prop…but it did just fine.

 

[stresspoint]

i was contemplating converting my Maxum SR1800 with a 4.3 to a 5.7 V8 ,
after looking into the amount of work to move things and make stuff fit, and advice from people i decided against the conversion ,
that being said , i hindsight , with all the trouble i went to to get a 4.3 to how i wanted it i probably would have been better off because good 4.3 and Am parts are rare here in Australia so i had a hell of a time getting the 4.3 right .

its a good thing i stuck with it and kept the 4.3 , i love the way that little motor performs , the boat seems to be built for a motor that size. .

something to keep in mind if you decide on going the conversion to a V6 or V8 is whether or not your boat will be suited to a bigger more powerfull motor ,
my advice is to stick with what the boat was built for , conversions are always a hit or miss whether or not the live up to expectations ,
you know your boat and it appears it has sentimental value , spend the effort and money to build a good 3.0 , maybe do some performance mods and later model upgrades if available for that motor ,

once you start chopping you cant ever bring it back to original again .

 

[Dubed]

I have a 3.7 190 hp. Its a love / hate thing for sure.

I did all the research and decided to have the thing fully rebuilt and replaced all the bolt-ons, alternator conversion, pertronix upgrade. All is working well (for now) and am happy with it.
I just cant see a 3.0 135 hp, 180 ft lbs of torque moving my almost 22 foot Chris Craft. The 3.7 is lighter, has 55 more horse power and an extra 95 ft lbs of torque. Maybe Im wrong, but Im pretty sure it would suffer tremendously getting a larger boat on plane.
Anyways, I rebuilt and moved on. Any comparable power to weight combination is going to be a huge undertaking. If Im looking to repower again some day it will be because parts are unavailable for the 3.7, no other reason.
Good luck with your project!

 

[Scott Danforth]

the seville 19' CC also came with a 305 V8.

plenty of room for a V-motor.

 

[nola mike]

Why would anyone even consider going through the trouble and expense of a repower and go *down* in power? 4.3 is a decent bump over the 3.7, definitely a smoother engine. The extra weight makes a big difference. 3.7 is plenty reliable once the original sins of the engine are taken care of. Parts a bit tough to find, but you only need one of each exhaust part and they last a long time with the closed cooling. Also plugs, oil filter, other maintenance tougher depending on access. If your boat can handle it, a 5.7 is a no brainer

 

[Dubed]

Why would anyone even consider going through the trouble and expense of a repower and go *down* in power? 4.3 is a decent bump over the 3.7, definitely a smoother engine. The extra weight makes a big difference. 3.7 is plenty reliable once the original sins of the engine are taken care of. Parts a bit tough to find, but you only need one of each exhaust part and they last a long time with the closed cooling. Also plugs, oil filter, other maintenance tougher depending on access. If your boat can handle it, a 5.7 is a no brainer

Yes, yes, and yes.
The final decision maker for me was the fact that I dont have a garage or barn big enough to house the boat. If I did I would have spent the winter dropping in a V-motor. Tackling that large and lengthy of a project in my driveway was out of the question.

 

[QBhoy]

I have a 3.7 190 hp. Its a love / hate thing for sure.

I did all the research and decided to have the thing fully rebuilt and replaced all the bolt-ons, alternator conversion, pertronix upgrade. All is working well (for now) and am happy with it.
I just cant see a 3.0 135 hp, 180 ft lbs of torque moving my almost 22 foot Chris Craft. The 3.7 is lighter, has 55 more horse power and an extra 95 ft lbs of torque. Maybe Im wrong, but Im pretty sure it would suffer tremendously getting a larger boat on plane.
Anyways, I rebuilt and moved on. Any comparable power to weight combination is going to be a huge undertaking. If Im looking to repower again some day it will be because parts are unavailable for the 3.7, no other reason.
Good luck with your project!

Think the 3.7 I referred to was 170hp. Was replaced with a 3.0 with apparently 30hp less.

 

[Dubed]

Think the 3.7 I referred to was 170hp. Was replaced with a 3.0 with apparently 30hp less.

Makes sense, still a little weak but very reliable, budget friendly and servicable.
Still, if I was to do it differently, I would go with the 4.3 if the transom and outdrive were all good. If they needed replacement, probably a 5.7.
Why not at that point anything goes.

 

[QBhoy]

Makes sense, still a little weak but very reliable, budget friendly and servicable.
Still, if I was to do it differently, I would go with the 4.3 if the transom and outdrive were all good. If they needed replacement, probably a 5.7.
Why not at that point anything goes.

Yeah. Totally get that. Just depends on ability and cost I suppose. The requirement for glassing in new mounts for them might scare some from the idea perhaps. Lots to change that way for sure. No doubting the 3.0 for it’s reliability…had one in the early days and know of loads in friends boats. I don’t think I could have another 4 cylinder like that in a boat though. Just very coarse on the ears, if you used to a lovely big V8 mpi like my inboard boat has. Not to mention the performance, haha. Each to their own though.

 

[Lou C]

Makes sense, still a little weak but very reliable, budget friendly and servicable.
Still, if I was to do it differently, I would go with the 4.3 if the transom and outdrive were all good. If they needed replacement, probably a 5.7.
Why not at that point anything goes.

For a 22 ft boat I'd go 5.7. I have a 4.3 in a 20' (heavy for its size) and that's about as big a boat that IMHO that a 4.3 feels good in, and that's with a 4bbl carb. Beyond that you want the extra torque of the V8. So if you're going to do it, go all the way.

 

[QBhoy]

For a 22 ft boat I'd go 5.7. I have a 4.3 in a 20' (heavy for its size) and that's about as big a boat that IMHO that a 4.3 feels good in, and that's with a 4bbl carb. Beyond that you want the extra torque of the V8. So if you're going to do it, go all the way.

Likely right Lou, if it all lines up for the fella. But with regards to the 4.3…I’ve had these in a bayliner 2255 cruiser and a more powerful VP version in a heavy built sealine 23ft 4 berth. That weighed over 2 tons with fuel in her. She did just fine with that old 4.3. Was the 205a. I’m sure the duo props helped her out a bit perhaps. But she accelerated to 20 mph quicker than most speedboats with 3.0’or similar. She’d do 35/36 mph gps flat out from memory too. My point is, most 4.3’s do well I think. Even in bigger heavy boats. That one in particular never struggled to plane with any amount of people onboard. Never touched the trim tabs on her either.

 

[Dubed]

For a 22 ft boat I'd go 5.7. I have a 4.3 in a 20' (heavy for its size) and that's about as big a boat that IMHO that a 4.3 feels good in, and that's with a 4bbl carb. Beyond that you want the extra torque of the V8. So if you're going to do it, go all the way.

Yes, but for affordablity the 4.3 all the way. They are plentiful and he can use his existing outdrive which is huge. Most of us wouldnt be on these forums if money wasnt an object!

 

[nola mike]

Yes, but for affordablity the 4.3 all the way. They are plentiful and he can use his existing outdrive which is huge. Most of us wouldnt be on these forums if money wasnt an object!

5.7 just as plentiful, parts maybe cheaper. Drive isn't a big deal. Find a used one on cl and sell yours.