4.3L Mercruiser Milkshake

[Lukey220]

What size boat are you putting the new engine in?
If its a 17-19 footer then why not just get a late model Vortec 4.3 with a 4bbl carb? That will make the whole thing simpler and cheaper, you will need to use an electric fuel pump and a Vortec intake manifold but other than that it should be an easy swap.
If you have a 20-21' then going to the V8 makes sense, but there are extra costs, exhaust system for one, carb has to be rejetted but most of all is making that 1.81:1 gear ratio work with the V8.
I had the same thoughts with my boat which is a heavy 20' with the 4.3, I'd like to go to the V8, the drive in mine (Cobra) is a 1.62:1 so it might be do-able. If not I have no problem with a Vortec V6 since the fuel economy is quite good for this size boat.

It’s an 18ft light boat , I was more leaning v8 because of the good deal it would have been. It includes the exhaust parts I need aswell. I will look into a vortec block aswell.
Thanks Lou!

 

[Lukey220]

It’s an 18ft light boat , I was more leaning v8 because of the good deal it would have been. It includes the exhaust parts I need aswell. I will look into a vortec block aswell, they were just harder to find.
Thanks Lou!

 

[Scott06]

Damn… my 4.3l is definitely 1 piece main seal as my bolts are Center on covers.

Huge bummer that it won’t work, thanks for catching that guys! Is there adapters for the couplers or anything to make the swap work or am I SOL?

You only need the earlier two piece rear main seal coupler and maybe a different starter
this coupler works with the earlier two piece rear seal

MerCruiser Hub Style Coupler (1985-Earlier)

This coupler is used on pre-1985 MerCruiser 350 ci or 305 ci engines, with what is commonly called a "two-piece rear main seal" or "split seal".Replaces MerCruiser part #76850A2

www.michiganmotorz.com

Starter - there are only two chevy patterns (regardless of engine size)straight and staggered that are related to flywheel size- something to look at.

Just keep in mind this is a pre-1985 engine with perimeter valve cover bolts, should be a good price otherwise you may be better off holding out for a vortec 4.3 or 5.7.

 

[Lukey220]

You only need the earlier two piece rear main seal coupler and maybe a different starter
this coupler works with the earlier two piece rear seal

MerCruiser Hub Style Coupler (1985-Earlier)

This coupler is used on pre-1985 MerCruiser 350 ci or 305 ci engines, with what is commonly called a "two-piece rear main seal" or "split seal".Replaces MerCruiser part #76850A2

www.michiganmotorz.com

Starter - there are only two chevy patterns (regardless of engine size)straight and staggered that are related to flywheel size- something to look at.

Just keep in mind this is a pre-1985 engine with perimeter valve cover bolts, should be a good price otherwise you may be better off holding out for a vortec 4.3 or 5.7.

$1000CAD with new manifolds/elbows, and electric ignition module/kit. Rebuilt in early 2000’s, 700 hours since rebuild, Which is a much better deal than any other motors near me.

Will the older style coupler still mate with my alpha shaft?

 

[jimmbo]

A 5.7 in a 18 1/2 to 19 ft is just about Perfect. I have been running one for 20yrs and it almost accelerates like an outboard
View attachment 367328-29272d49aa41ed5220980ce0822f647d.m4v

 

[Scott06]

$1000CAD with new manifolds/elbows, and electric ignition module/kit. Rebuilt in early 2000’s, 700 hours since rebuild, Which is a much better deal than any other motors near me.

Will the older style coupler still mate with my alpha shaft?

I think yes but you may want to verify with a place like Michigan Motorz

 

[Lou C]

that's the part that is tricky and not sure if the length of the driveshaft splines changed, or what might have happened...I guess if you could compare parts numbers that might tell you if the driveshaft was the same part number for both coupler designs, then it might work, otherwise, hard to tell.

 

[Lukey220]

that's the part that is tricky and not sure if the length of the driveshaft splines changed, or what might have happened...I guess if you could compare parts numbers that might tell you if the driveshaft was the same part number for both coupler designs, then it might work, otherwise, hard to tell.

When pulling up specs for an alpha one gen 1 driveshaft it says “Fits 1972-1990 R, MR and Alpha one” which seems to me like it should be the same driveshaft and coupler splines.

 

[Scott06]

When pulling up specs for an alpha one gen 1 driveshaft it says “Fits 1972-1990 R, MR and Alpha one” which seems to me like it should be the same driveshaft and coupler splines.

Thats what i also thought so yiu should be ok with that coupler for earlier engine.

that is backed up by the parts digram listing the different couplers for early and later models shows studs and hardware sizes to hold coupler to crank vs later flywheel attachment

MerCruiser 260 GM 350 V-8 1982-1986 Crankshaft & Pistons Parts

MerCruiser 260 gm 350 v-8 1982-1986 crankshaft and pistons parts. Buy a genuine Mercury Quicksilver or aftermarket part.

www.marineengine.com

 

[Lukey220]

Also contacted Michigan motorz and they said all splines/couplers are the same for the drives! Looks like I should be good to go with a flywheel and new coupler for the 350. Thanks for the help everyone!

 

[nola mike]

Youso contacted Michigan motorz and they said all splines/couplers are the same for the drives! Looks like I should be good to go with a flywheel and new coupler for the 350. Thanks for the help everyone!

Yoke length was different on the inline mc-1s and earlier iirc. 84 should be an alpha and the vee engines were always the same. Either way the yoke can be swapped easily. @Bondo can confirm

 

[Bondo]

Yoke length was different on the inline mc-1s and earlier iirc. 84 should be an alpha and the vee engines were always the same. Either way the yoke can be swapped easily. @Bondo can confirm

Ayuh,.... Yer correct, 'n only the GM in-line motors,.....

 

[Lukey220]

Ayuh,.... Yer correct, 'n only the GM in-line motors,.....

Very impressive how much you all know. Thanks a lot to all!

 

[Lou C]

It's good when these questions get asked because then we all learn.

 

[nola mike]

Ayuh,.... Yer correct, 'n only the GM in-line motors,.....

Did Ford make an inline?

 

[Bondo]

Did Ford make an inline?

Ayuh,..... Ford made all kindsa in-lines, but Merc never used 'em,.....

The ole 470s were both Ford, 'n GM parts, but did not use the short input shafts,....

 

[Lou C]

OMC used a Ford 2.3 liter inline 4 (from the Pinto/Bobcat and others)
Ford built a 250 cu in six and a 200 cu in years ago and their best was a 300 cu in six
None used in boats though
I'd take one of those all cast iron Ford 300 cu in (4.9) liter beasts over any of the aluminum and plastic crap they sell today....
I kept my '98 Grand Cherokee with AMC's classic 4.0 liter inline 6 for that same reason...durability and simple design..... The new Pentastar V6 has like 100 more peak HP but I doubt they are going to last as long.

 

[nola mike]

Ayuh,..... Ford made all kindsa in-lines, but Merc never used 'em,.....

The ole 470s were both Ford, 'n GM parts, but did not use the short input shafts,....

Yeah, I meant in a Merc application. I'm sure we can agree that the 470 was special.

 

[Rick Stephens]

Yeah, I meant in a Merc application. I'm sure we can agree that the 470 was special.

I love it. 'Special'.

 

[Lou C]

check out what Merc charges for "their" 4.5 V6 parts compared to GM 4.3 parts prices (that they obviously copied)...that's special!