Any tips on a Mercruiser/OMC 120 engine rebuild?

[wrfalpacas]

Ok, So I have 2 engines, a 68 2.5L mercruiser and a 71 2.5L OMC. The mercruiser has a welded crack repair in the block, and smokes. The OMC is what I was going to replace it with.

Question 1: Do I need to get a reman head with hardened valves and seats for unleaded gas or have the head redone?

Question 2: Are the engines interchangeable, or are there problems with a direct swap?

Question 3: While the engine is out, are there any easy mods I can do to get a little more horsepower?

Question 4: Is an electronic ignition system a good investment for this engine?

Question 5: Are there any differences in the accessories such as fuel pump, that are better on one brand vs the other?

Thanks in advance!

 

[IVAZ]

Re: Any tips on a Mercruiser/OMC 120 engine rebuild?

1- If the head you?re going to use is in good shape you can leave it alone. Some guys use lead additive. Others just run it with regular unleaded.

2- They should be interchangeable.

3- I don?t know of any upgrades. It?s probably best to get it running before you start digging into it, unless you are really sure of what you?re doing.

4- Again, I would get it running before I started changing the way it was set up to run.

5- Keep all the Merc accessories with the Merc. Swap them to the donor engine.

 

[Fishermark]

Re: Any tips on a Mercruiser/OMC 120 engine rebuild?

Ok, So I have 2 engines, a 68 2.5L mercruiser and a 71 2.5L OMC. The mercruiser has a welded crack repair in the block, and smokes. The OMC is what I was going to replace it with.

Question 1: Do I need to get a reman head with hardened valves and seats for unleaded gas or have the head redone?

Not necessary. If the head is good, then go with it.

Question 2: Are the engines interchangeable, or are there problems with a direct swap?

Direct swap.

Question 3: While the engine is out, are there any easy mods I can do to get a little more horsepower?

The only easy "mod" would be to replace it with a 3 liter - still a direct swap, but with more horsepower.

Question 4: Is an electronic ignition system a good investment for this engine?

I think it is a good idea - I know others disagree. But the electronic ignition gives a more reliable and steady performance.

Question 5: Are there any differences in the accessories such as fuel pump, that are better on one brand vs the other?

Don't know