TOPIC: 140HP Mercruiser engine compatability?

friends,

i'm sure that at least one of you has the correct answer to this question:

my 120HP Mercruiser engine in the 1970 SternCraft I/O utility is TOAST.- the block is badly cracked.
(this is my first rig with a Mercruiser I/O system.)

this morning, i got an email from a local man who has a 1985 vintage, 140 Mercruiser, which he says was rebuilt last year, before the boat that it is in was "wiped-out" in an accident- the hull is unsalvageable, after hitting a large concrete pier at speed.
(he says that the collision damage is confined to the fore section of the hull & that i can have the whole works for 300.oo.)

my question is this: is the 140HP Mercruiser of 1985 similar enough to the 1970 model 120HP engine to use the same mounts, outdrive, etc?
OR
do i have to change out the whole drive system?
OR
should i pass on the whole thing & seek an earlier & perhaps more suitable engine?

THANKS, satx

There were some differences in the manifold & riser that took place but I believe they may have been few years later. Simply take a look at the manifold/riser & if they look alike, they will interchange. (The 120 manifold & riser is different that a 140 but they look similar. You will notice the orientaion of the carb is 90 degrees different between the 2. You will need to swap the exhaust "bellows" just below the riser and the exhaust pipe below that too.) If the riser is round vs square in cross section so to speak then there will be issues with the exhaust. The core engine and forward mounts will be interchangeable.

You will find differences in the shift, throttle & wire harness. If you know what you are doing, you will be able to swap things around & make it work.

Biggest issue you need to work thru is that your shift linkage is transom mounted & uses a reverse lock valve. The later engines mounted the shift linkage on top of the engine and did not use a reverse lock valve. You will need to use the shift linkage/reverse lock valve on the transom and that will include using the shift interupter switch on the transom so you may need to do some creative wireing.

jimandros,

the Balboa 17 Sterncraft came with the 120MC standard & with the 140MC & 165MC optional, so the engine should be suitable from a powering standpoint. - mainly what i wondered about was the differences between the 1970 vintage 140 & the 1985 vintage 140 & whether the later engine would work with the early OD.

THANKS for answering.

yours, satx

The cylinder block & head will be bolt in.

It is the possibility that the manifold/riser is different that "may" cause issues. I say "may" because of the compatability of the riser aligning with the exhaust tube below. Also, 120 used a different size riser, rubber connector bellows and exhaust tube than a 140/165. Again, if that 1985 still used the original manifold design, so you "should" be OK.

So, again, I give you a "should" because the 1985 will be an Alpha generation 1 drive. So the transom plate & outer bell housing is different. I am not sure if the exhaust tube will bolt up if required to swap it out. If not, then you are looking at replacing the transom plate & outdrive too. Also, when they went to the MR/Alpha drive in '84, the length of the "donkey dick" or u-joint shaft was standardized from the short inline engine length to the longer V6/V8 length.

Bottom line as I stated last night is IF the manifolds look similar, then it will bolt in except for swapping the exhaust tube. If the manifolds are not similar, then it becomes much more complex.

When you 1st got this boat, there was a question as to if it was a 120 or 140. Was that ever resolved? Is there a possibility that your cracked engine is a 140? That would simplify things a bit anyways.

jimandros,

YEP, the original engine is a TRASHED (standard for the Balboa 17) 120. - i had it looked at by someone who should know.- he said that, according to the SN that it's the 153CI/2.5L block.
(as you've doubtless guessed, i'm far from expert on Mercruisers.- until now, my inboard experience has been limited to the old traditional inboard Crysler Crown engines & the Hercules-based & GM-based Chris-Craft engines.)

THANKS, satx

to ALL,

well, i FOUND the answer in the CLYMER's manual for Mercruisers of that era.

NOPE. it won't work W/O a MAJOR surgery to the transom, as the post 1982 engine AND the OD are UNsuitable, because even the "hole" in the transom is different.

sorry, satx