1978 mercruiser 5.0

[kershawD]

I have a 1978 slickcraft sc240 project boat that original had a merc 5.7 260hp motor with a Merc1 outdrive . previous owner had pulled the original motor and all hoses,wiring ,mounts and brackets out of the boat. all thats left is the outdrive, exhaust Y, trim pump. and power stearing pump. I recently aquired a 1978 OMC 5.0 with a trailer load of parts . bell housing , (altinator- no brackets). pulleys. 2 starters. exhaust manifolds and 2 elbows, front engine mount. complete steering assembly. what parts would I need to set this OMC 5.0 where a merc 5.7 was? I have searched for pictures of boats like mine and nothing! most marine parts web sites dont have pictures of the parts or any good diagrams of older mercruisers. any help would be great. thanks

 

[Bondo]

Ayuh,..... Welcome Aboard,.... The only thing in that pile of OMC parts that is any Good for yer project is,....
The bare basic Long Block,.....
The Chevy part of it,....
All the OMC stuff is useless,..... Incompatible with the Mecruiser drive,.... Won't fit together,....

 

[Scott Danforth]

unbolt everything except the block, heads, waterpump, oil pan and intake manifold, and go from there. even the carb and distributor is different

 

[kershawD]

I have stripped down the long block , checked all internals and had the block cleaned and checked. the block is a in excellent condition. im going to just re ring the engine remove cylinder glaze with a hone. i have built many engines for various cars and trucks. this will be the first marine engine for me. I have ordered marine engine overhaul kit. and all new stainless fasteners. for sheet metal parts. my next question is can I use after market intake manifold for cars or does it have to be marine? im wanting to use the edelbrock rpm airgap dual plane hi rise manifold.

 

[kershawD]

this is the 1978-9 OMC 305

 

[kershawD]

I will have the long block complete and ready to run. I will take pictures of the engine compartment of my boat and of all parts i have so maybe someone could help me find the parts i need to complete this project.

 

[kenny nunez]

Take a look at the flywheel bolt pattern, the earlier engines were larger than the later models and you may have to buy a new shaft coupler. If the 305 has a 4 barrel use the Mercruiser carburetor because the linkage is opposite than the OMC, if the 305 has a 2 barrel swap the manifolds, the camshafts are the same and you should have around 230 hp. Set the engine up and run it before you install it and make any adjustments as well watching for any leaks.

 

[kershawD]

yes it has the 4 barrel intake and quadrajet carb. im just going to order a new [h=1]JET 33005 Marine Quadrajet Carburetor.[/h]