1979 3.0 140 mercruiser engine swap to 1988 3.0 engine

[Barney555]

1979 Mercruiser MC1 3.0 140 engine (needs full rebuild) Also MC1 outdrive seems ok( new impeller and oil)


Can I drop in a 1988 3.0 130 mercruiser, and make it work with existing transom assembly?
From what I can tell, my issues will include:

1. motor mounts are wider on MC1 transom plate
2. exhaust riser offset to port side on newer manifold ( 2 bolts vs 4 )
3. shifter assembly mounts on transom, versus top of engine on newer motor
4. distance from outdrive to new motor coupler (yoke length?)

Gimbal and bell housing needs new bellows and seals/gaskets and probably new gimbal bearing. I can do all that no prob. Power trim works well, minus trailer stop switch( common fail)
Im wondering if this is doable, or would I be wasting my time trying to make it work?

 

[Bondo]

Ayuh,.... Welcome Aboard,...... Ya, there are a few differences, but so long as you have the ole MC-1 parts, it should be a straight forward swap,.....
Very doable,....
I'm not sure just how the down-pipe swap goes,.....
Shifter plate shouldn't matter, where ever it fits best,....

 

[Scott06]

1979 Mercruiser MC1 3.0 140 engine (needs full rebuild) Also MC1 outdrive seems ok( new impeller and oil)


Can I drop in a 1988 3.0 130 mercruiser, and make it work with existing transom assembly?
From what I can tell, my issues will include:

1. motor mounts are wider on MC1 transom plate
2. exhaust riser offset to port side on newer manifold ( 2 bolts vs 4 )
3. shifter assembly mounts on transom, versus top of engine on newer motor
4. distance from outdrive to new motor coupler (yoke length?)

Gimbal and bell housing needs new bellows and seals/gaskets and probably new gimbal bearing. I can do all that no prob. Power trim works well, minus trailer stop switch( common fail)
Im wondering if this is doable, or would I be wasting my time trying to make it work?

As outlined you should have everything to mix and match components to make it work.

Use the MC-1 flywheel cover to match your MC-1 mounts.

Riser offset you may have to mix and match or use marine hard wall exhaust hose. Shifter assembly - as Bondo mentions it can go where ever is easiest, if you can mount it to the valve cover adjustment may be easier

Yoke length should be the same (couplers as well) I think the only odd balls were early inline 6s with a shorter dive shaft yoke. you can swap in a later and longer one at the joint.

This is totally doable, but you may want to consider upgrading to the later Alpha one transom and outdrive if you really like the boat and want to keep it. While the MC1 is a good design and relatively robust you may run into parts availability issues.

 

[nola mike]

Yoke length should be the same (couplers as well) I think the only odd balls were early inline 6s with a shorter dive shaft yoke. you can swap in a later and longer one at the joint.

IIRC all inlines except the 470 used the shorter yoke on the MC-1

 

[Scott06]

IIRC all inlines except the 470 used the shorter yoke on the MC-1

Could be maybe can swap coupler off old engine to match yoke not. I don’t think the 3.0 changed coupler or flywheel until 1990 ish when single piece real main seal was implemented

 

[nola mike]

Could be maybe can swap coupler off old engine to match yoke not. I don’t think the 3.0 changed coupler or flywheel until 1990 ish when single piece real main seal was implemented

Yeah I think the coupler changed when the RMS changed, dunno what the change is that required yoke length change. Rear mounts/flywheel cover?

 

[Scott Danforth]

As for the 3.0 base motor. the 1988 is same as the 1974.

Unbolt remove old, bolt in the new.

 

[Scott06]

Yeah I think the coupler changed when the RMS changed, dunno what the change is that required yoke length change. Rear mounts/flywheel cover?

Yes one piece rms went to flywheel mounted coupler vs one on studs coming off crank hub. Not sure if it was the mc1 to R/MR/alpha gen one that must have made coupler shorter . He should have both couplers so should be able to mix and match a solution

 

[Scott Danforth]

Crank and flywheel changed for 1991 when GM retooled the 3.0

 

[Barney555]

thanks for all your input! this really helps.
I was thinking about swapping transom assembly to alpha might make more sense. If I go that route, would the older MC1 outdrive bolt up to it for now and I could upgrade that later on, or would I need a new alpha 1 drive as well? Thanks again!

 

[Scott Danforth]

Just swap the motor for now. Look for a complete post 1991 3.0 /A1G2 later

 

[Scott06]

thanks for all your input! this really helps.
I was thinking about swapping transom assembly to alpha might make more sense. If I go that route, would the older MC1 outdrive bolt up to it for now and I could upgrade that later on, or would I need a new alpha 1 drive as well? Thanks again! View attachment 392782

Yes a mc1 will bolt up to a later R, MR, or alpha one gen one drive.
as Scott mentioned if you do the swap might be worth going to the c1991 and up gen 2 set up.

have you checked your transom normally all that sealant slapped around the transom housing is indicative of transom rot

 

[ROY WILLIAMS]

thanks for all your input! this really helps.
I was thinking about swapping transom assembly to alpha might make more sense. If I go that route, would the older MC1 outdrive bolt up to it for now and I could upgrade that later on, or would I need a new alpha 1 drive as well? Thanks again! View attachment 392782

I was the 1978 outdrive the picture 2023

View attachment 392782

my the outdrive MR 1978 ...

 

[Barney555]

Yes a mc1 will bolt up to a later R, MR, or alpha one gen one drive.
as Scott mentioned if you do the swap might be worth going to the c1991 and up gen 2 set up.

have you checked your transom normally all that sealant slapped around the transom housing is indicative of transom rot

Thanks, good point.
Checking transom from inside, and there's some rot where water drains to bilge, but around transom assembly seems solid. I will do a full inspection and repair what's needed.

 

[Barney555]

I was the 1978 outdrive the picture 2023


View attachment 392786

my the outdrive MR 1978 ...

that looks just like mine, except bell/gimbal housing has trim senders and switch on sides. Mine does not. Looks nice and clean, How is it working for you?

 

[Scott06]

Thanks, good point.
Checking transom from inside, and there's some rot where water drains to bilge, but around transom assembly seems solid. I will do a full inspection and repair what's needed.

you can go to the resto forum and see how folks check with drilling small holes. Unfortunately likely will need replacement, its pretty insidious how rot will migrate through a boat

 

[Scott Danforth]

Thanks, good point.
Checking transom from inside, and there's some rot where water drains to bilge, but around transom assembly seems solid. I will do a full inspection and repair what's needed.

I smell a full hull restoration.

 

[ROY WILLIAMS]

that looks just like mine, except bell/gimbal housing has trim senders and switch on sides. Mine does not. Looks nice and clean, How is it working for you?

WELL MY 1978 BOAT/MCM470 ENGINE DECADES DID THE REPAIRS . EXCELLANT !
THE boat is no rotted wood it ...20 ft Wellcraft .... did the wood / fiberglass coated it ...
I was the gimbal inspect it every year .. did the grease and the outdrive .. gear oil draining it ..also the impeller around 3 yrs ago ...
the trim senders fixing it also the engine switch ignition distributor ...did the shift cable switch