Engine Swap

Hello to all,
Quick question , have an 85 OMC 2.5 and would like to swap in a complete (engine & outdrive) mercruiser setup . Preferably 3.0 or 4.3 of around the same year model. Seems the Mercrusier units are more durable and easier to find replacement parts.
Reason? Boat was a gimme ...Great shape !!! but engine appears to be locked up and plenty of water in oil ...still very new to boat mechanics
(auto tech forever though )
Any suggestions ? Or am I getting the wrong feeling about OMC engines & drives ? Any help would be greatly appreciated .
wrnutsdad
1985 Renken 17'
OMC 2.5

Re: Engine Swap

The impracticality of the swap is the reason the boat was a gimme.

You would have to plywood/fiberglass the hole shut in the transom, and basically refit as a boat builder would do from new.

You need Mercruiser engine and drive complete, steering system right to the steering wheel, and throttle/shifter, and even gauges would be a nightmare to wire up. You would need to be a wiz on electrical to make it all work.

And in the end... you'll hate a 4.3 when your boat has a little 15 gallon fuel tank like most 2.5 powered entry level boats....horrible range.

Old boats are worth less than old boat parts.

In the quest for a 4.3 donor, you'll probably find yourself the boat you really want.

Re: Engine Swap

If you really like the hull and it's in truly good shape, then you can repower without too many problems.

As has been mentioned you'll probably want to rebuild the transom, although you can also buy an adapter plate for it.

Depending on the OMC drive it may be worth fixing the engine, or not. If it's one of the better OMC models, it may run for a bit, or people may also be willing to buy the parts off your boat to fix their drives.

First thing, I'd make sure the boat is truly in good shape. Do a drill test on the stringers to make sure they're not rotten, and on the transom if you're going to use an adapter plate (if you're not, you're replacing it anyway).

Probably you'll need to create/install new motor mounts too, so I wouldn't worry about those.

If the hull is in good shape and you're sure you like the design, then look at the engine... either repair it or replace the whole drive trail (you can't mix OMC and Mercruiser).

To get a replacement drive train, look for a cheap boat with an alpha or pre-alpha series drive. Expect the engine to be bad, and probably the lower unit too. Get all the parts in between the two, including the trim pump and cylinders, motor flywheel cover, and bolts. Replace/fix the engine, install it and the transom kit in your new transom on the boat, then buy an SEI lower unit (replacement for Mercruiser, cost is about $1400 installed) and you're good to go.

If you're lucky and you find a boat with a good engine/drive that's been in an accident that messed up the hull, then you can swap that in piece by piece.

If you can't find a replacement drive train in a scrap boat then you'll need to pay probably $2k or so to get the parts piecemeal, or else pay $8k-$10k to a dealer for new.

So.... if you really, really like the boat (the way it looks) AND you can verify that it's in good shape by checking all the wood under decks for rot and water (unlikely to be dry, but possible) then you can look at the engine swap.

Or, just go look for boats that have good drive trains... if you find one that's cheap enough for you and you like the look, then fix the hull on that one and scrap the one you have

Erik

Re: Engine Swap

Once again, cheap and/or free boats are rarely a bargain!

Re: Engine Swap

car mecanic advice ...

unless the OMC outdrive is that bad ( this is the part I dont know),

a 2.5L or a 3.0L are the same either OMC or mercruiser ...
so rebuilding a 2.5 or 3.0 they will last the same .....
if your engine block is ok ...it`s still a chevy engine : cheap parts
( this is the part I know )

Re: Engine Swap

erikgreen said:

you can also buy an adapter plate for it.

Click to expand...

huh? where?

Re: Engine Swap

Thanks to all who answered. You gotta love experience .. probably saved me a ton of headaches and cash !! May just tear the engine down see exactly what is wrong try to patch it as cheap as possible and take the kids out a couple of times untill it breaks .. Found out that the entire lower drive unit was just replaced 3 yrs ago , but only used a few times this past summer. Boat owner passed away 3 yrs ago .. right after unit replacement...Grandson got the boat last summer and now its broke.
New question ...are the gaskets ,bearings ,valves and other internal engine parts the same as automotive applications ?
Once again THANK YOU !!! This is a great forum and I look forward to participating in it ...who knows I may have an answer or two for someone one day myself...
wrnutsdad

Re: Engine Swap

http://www.sterndrive.cc/mm5/merchant.mvc?Screen=PROD&Product_Code=9D-116&Category_Code=Cobra

Re: Engine Swap

Alpheus said:

http://www.sterndrive.cc/mm5/merchant.mvc?Screen=PROD&Product_Code=9D-116&Category_Code=Cobra

Click to expand...

?
not gonna help anyone here. he has a 1985

Re: Engine Swap

Yep. You are correct sir... Slipped that one by me...