Mercruiser 305 Engine Replacement options

[Ragnarokii]

Hello All:

I have a 1998 two bolt crank, one piece seal, Vortec Head, roller cam, GM based Mercruiser 305 with Carb. Before the damage, the engine had low hours, and is in "great" shape. Block has cracking from freezing, and now out of the boat.

I also have a 1984 305 out of a Iroc Z, low miles, with Edelbrock performer intake and Edelbrock carb (model 56 I think). It's missing the distributor (it was stolen) and flywheel (didn't come with the engine).

I'm looking for the most economical, safe, and reasonable way to get the boat back on the water. I'm looking for opinions:

- All of my original mercruiser bolt on parts are in great shape (pumps etc) and I plan to re-use these with any solution I go with.
- I can pick up a new style long block for around $1,800, bolt on my heads, intake, etc from the original engine, and off I go.
- I have not found a clean block with the original bore size that I could bolt my existing engine internals into, and I've been told they are non-existant, mostly due to bad winterizing creating a huge demand for them.
- To use the Iroc block, do I need a marine cam? I've seen them for around $120 (flat tapets). What do I need to do the edelbrock carb to marinize it, if this is even possible? I can't use my old mercruiser carb because the profile is half the size of the edelbrock. And the mercruiser intake manifold won't fit on the 84 block. I had one auto mechanic tell me that I could just bolt my vortec heads onto the 1984 block, put the mercruiser intake and carb on it, and I'd be good to go. Another told me that wouldn't work because of the roller cam.

So before I start tearing the 84 block apart, I thought I'd ask for your experience/opinions on the best way to go.

Thanks!

 

[John_S]

Re: Mercruiser 305 Engine Replacement options

- I can pick up a new style long block for around $1,800, bolt on my heads, intake, etc from the original engine, and off I go.

That's my vote.

 

[RogersJetboat454]

Re: Mercruiser 305 Engine Replacement options

- I can pick up a new style long block for around $1,800, bolt on my heads, intake, etc from the original engine, and off I go.

Not a bad idea. Every things fresh. No mixing/matching/searching for parts. You will have all the original performance your Vortec 305 had.

Allot of people on this site have bought long blocks from these guys; http://www.rapidomarine.com/default.aspx?p=/engines/default.aspx
Most have had good things to say, a few have had problems, I have no personal experience with them. They are charging less for a 350 long block than what you have been quoted for a 305, with no core charge and reasonable freight charges.

- I have not found a clean block with the original bore size that I could bolt my existing engine internals into, and I've been told they are non-existant, mostly due to bad winterizing creating a huge demand for them.

Wouldn't even go there. Lotta work for something that may not work out if the block or your parts aren't pristine, and require work.

- To use the Iroc block, do I need a marine cam?.

Yep.

What do I need to do the edelbrock carb to marinize it, if this is even possible?

Probably replace it. This would be a good question for edelbrock. A dedicated marine carb usually has the float bowl vents situated in such a manner that they dump any raw fuel from an overfilled float bowl into the venturis of the carb, rather than outside of the carb, which would be an explosion risk on a boat.

I had one auto mechanic tell me that I could just bolt my vortec heads onto the 1984 block, put the mercruiser intake and carb on it, and I'd be good to go. Another told me that wouldn't work because of the roller cam.

Technician A is right, Technician B is full of Poo...
Lotsa flat tappet engines with vortec heads installed out there. You will need the correct length push rods, self aligning rockers, and vortec intake manifold to make it work. But.... if your block cracked, theres a good chance your heads may be cracked too (and your intake and your exhaust manifolds).

Other thoughts....

You will need a flywheel (not a flex plate) for the 2 piece RMS on your '84. Depending on the size of the flywheel, your MARINE starter may or may not fit the older engine. You also need to be sure your coupler bolts to said flywheel. The core plugs should be changed to brass, and marine grade head gaskets should be used. The '84 heads are ca-ca compared to the vortec's, so if you use em, you will probably see a drop in performance. No telling how the pistons in the '84 compared to the newer engine are (dished, flat, etc) so your compression ratio may change a bit. Your exhaust manifolds if not cracked may be rusted to death (especially W/ saltwater use).

Personally I think I would be looking at a long block chief. Might be a nice time for a cheap upgrade to a 350.