Easiest engine drop in replacement for 1986 MCM 470

cdavy000

Petty Officer 3rd Class
Joined
Jun 11, 2023
Messages
97
Hello everyone, does anyone have any suggestions on what motor to get to replace current Mercruiser 470 (has valve issues that I do not want to deal with). I just wanted to see if anyone might have a good suggestion to make the swap as simple as possible, preferably an engine that still uses the same alpha one outdrive, but I am willing to replace it. I am looking at merc 4.3l v6 at the moment. Thanks all.
 

Scott06

Vice Admiral
Joined
Apr 20, 2014
Messages
5,829
Hello everyone, does anyone have any suggestions on what motor to get to replace current Mercruiser 470 (has valve issues that I do not want to deal with). I just wanted to see if anyone might have a good suggestion to make the swap as simple as possible, preferably an engine that still uses the same alpha one outdrive, but I am willing to replace it. I am looking at merc 4.3l v6 at the moment. Thanks all.
If it will fit in the doghouse or engine compartment a 4.3 will work great and be a power and reliability upgrade especially if you get a Vortec one with a 4 bbl carb (220 hp).

If you don't have room a 3.0 will drop in and if you go down 2" in prop pitch work with same drive gearing.

The 4.3 will gain some power and add some weight. 3.0 will give hp some power so if yo are already underpowered wouldn't do it. Either will be more durable and parts supportable than the 470.

Given the age of the boat would check the stringers transom and floor for rot before getting inve$ted

Somewhere on line merc publishes dimensioned drawings of the 4.3 and 3.0 showing mounting locations etc. was very helpful when I did a 4.3 to 5.0 swap
 

ScottinAZ

Senior Chief Petty Officer
Joined
Jun 25, 2009
Messages
755
I would agree with Scott... preference being on the 4.3. Keep in mind you will need a "new" bellhousing, and an actual y-pipe for the exhaust to mate the engine to your drive. These should be readily available, but if possible in your area, look for a derelict boat that someone is practically giving away with your desired engine in it. You will then get all the parts and accessories to complete the swap. Then cut up the other hull (after stripping it clean for spares) and sell the trailer. Mercruiser put the two engines of choice in nearly everything for decades, so you should be spoiled for choice.
 

cdavy000

Petty Officer 3rd Class
Joined
Jun 11, 2023
Messages
97
If it will fit in the doghouse or engine compartment a 4.3 will work great and be a power and reliability upgrade especially if you get a Vortec one with a 4 bbl carb (220 hp).

If you don't have room a 3.0 will drop in and if you go down 2" in prop pitch work with same drive gearing.

The 4.3 will gain some power and add some weight. 3.0 will give hp some power so if yo are already underpowered wouldn't do it. Either will be more durable and parts supportable than the 470.

Given the age of the boat would check the stringers transom and floor for rot before getting inve$ted

Somewhere on line merc publishes dimensioned drawings of the 4.3 and 3.0 showing mounting locations etc. was very helpful when I did a 4.3 to 5.0 swap
Very helpful thank you I figured the 4.3 would be a good fit
 

cdavy000

Petty Officer 3rd Class
Joined
Jun 11, 2023
Messages
97
I would agree with Scott... preference being on the 4.3. Keep in mind you will need a "new" bellhousing, and an actual y-pipe for the exhaust to mate the engine to your drive. These should be readily available, but if possible in your area, look for a derelict boat that someone is practically giving away with your desired engine in it. You will then get all the parts and accessories to complete the swap. Then cut up the other hull (after stripping it clean for spares) and sell the trailer. Mercruiser put the two engines of choice in nearly everything for decades, so you should be spoiled for choice.
That’s a great idea thank you I didn’t think of that. I was wondering though, why would the alpha one gen 1 outdrive/bellhousing not work with the 4.3l engine? I looked online and they seem to use the same gear ratio so I was hoping I might be able to reuse the bellhousing and outdrive from my current boat, thanks!
 

Scott06

Vice Admiral
Joined
Apr 20, 2014
Messages
5,829
I would agree with Scott... preference being on the 4.3. Keep in mind you will need a "new" bellhousing, and an actual y-pipe for the exhaust to mate the engine to your drive. These should be readily available, but if possible in your area, look for a derelict boat that someone is practically giving away with your desired engine in it. You will then get all the parts and accessories to complete the swap. Then cut up the other hull (after stripping it clean for spares) and sell the trailer. Mercruiser put the two engines of choice in nearly everything for decades, so you should be spoiled for choice.
I think the flywheel cover unless it is pre 1981 is should work. when the transition around '81 from MC1 to R/MR/Alpha one happened merc changed the distance between the rear motor Mounts. So unless you have a mc transom housing it should fit. You will need a wye pipe and yes easiest way is to find a complete tear out from a rotten glass boat
That’s a great idea thank you I didn’t think of that. I was wondering though, why would the alpha one gen 1 outdrive/bellhousing not work with the 4.3l engine? I looked online and they seem to use the same gear ratio so I was hoping I might be able to reuse the bellhousing and outdrive from my current boat, thanks!
 

ScottinAZ

Senior Chief Petty Officer
Joined
Jun 25, 2009
Messages
755
I think the flywheel cover unless it is pre 1981 is should work. when the transition around '81 from MC1 to R/MR/Alpha one happened merc changed the distance between the rear motor Mounts. So unless you have a mc transom housing it should fit. You will need a wye pipe and yes easiest way is to find a complete tear out from a rotten glass boat

did the 4.7 MCM motor use the same bolt pattern as the chevy? that is why I stated new bellhousing. I know Ford has several bellhousing patterns, Chevy is pretty universal, but no idea about what Merc used for the block on the 4.7. Changing engines gets exponentially harder when the engine doesnt bolt in.
 

cdavy000

Petty Officer 3rd Class
Joined
Jun 11, 2023
Messages
97
I think the flywheel cover unless it is pre 1981 is should work. when the transition around '81 from MC1 to R/MR/Alpha one happened merc changed the distance between the rear motor Mounts. So unless you have a mc transom housing it should fit. You will need a wye pipe and yes easiest way is to find a complete tear out from a rotten glass boat
Nice yeah it’s 1986 so I have the non MC version, it’s nice to hear that it will fit the current transom. I will make sure to find a Y pipe thank you
 

Scott06

Vice Admiral
Joined
Apr 20, 2014
Messages
5,829
did the 4.7 MCM motor use the same bolt pattern as the chevy? that is why I stated new bellhousing. I know Ford has several bellhousing patterns, Chevy is pretty universal, but no idea about what Merc used for the block on the 4.7. Changing engines gets exponentially harder when the engine doesnt bolt in.
I was under the impression the 3.7 used a Chevy bellhousing bolt pattern but could be FOS

Maybe @Scott Danforth or @nola mike may know

Scott and Mike - OP wants to swap his 3.7 for a 4.3 (preferred or maybe 3.0) does the 3.7 flywheel cover (alpha one gen 1 drive so later mount spacing) fit a chevy 4.3 block
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,944
yes, the 3.7 uses a GM flywheel bolt pattern same as 4.3. you do have to change the u-joint shaft.

the 3.0 is under powered and nearly the same weight as the V6.
 

nola mike

Vice Admiral
Joined
Apr 22, 2009
Messages
5,141
yes, the 3.7 uses a GM flywheel bolt pattern same as 4.3. you do have to change the u-joint shaft.

the 3.0 is under powered and nearly the same weight as the V6.
U-joint shaft is the same as well.
Op, *definitely* get a bobtail from a wrecked boat. Even a donor with a cracked block. The 4.3 blocks are easy to find, but all the stupid little parts that you'll need will either bankrupt you or slow you down and frustrate you.
 

cdavy000

Petty Officer 3rd Class
Joined
Jun 11, 2023
Messages
97
U-joint shaft is the same as well.
Op, *definitely* get a bobtail from a wrecked boat. Even a donor with a cracked block. The 4.3 blocks are easy to find, but all the stupid little parts that you'll need will either bankrupt you or slow you down and frustrate you.

U-joint shaft is the same as well.
Op, *definitely* get a bobtail from a wrecked boat. Even a donor with a cracked block. The 4.3 blocks are easy to find, but all the stupid little parts that you'll need will either bankrupt you or slow you down and frustrate you.
Awesome great to know thank you
 

cdavy000

Petty Officer 3rd Class
Joined
Jun 11, 2023
Messages
97
measure first a 4.3 is wider than any inline
I have one more question just to make sure, would the wiring harness be the same for both engines aswell? Would it just plug right into the 4.3? Thank you
 

Pmt133

Petty Officer 1st Class
Joined
Jan 6, 2022
Messages
303
I don't have that much to add but... While I didn't do an identical swap, I did do a 3.0l to a 4.3l. Make damn sure you have enough room for the mounts between the stringers... 24" minimum and even at that, it is tight.
 
Top