Mercruiser 2.5 / 3.0 interchangeable parts

Sea_Ray_Charles

New Member
Feb 19, 2019
1
Boat Info
1968 Sea Ray SRV 170
Engines
2.5 Litre GM 153 Ci 120 hp
Greetings,

I need to re-power my 1968 Sea Ray SRV 170. It had a Mercruiser 2.5 Litre (120 HP) 4/cyl GM 153 ci engine which eventually suffered the results of a malfunctioning exhaust manifold. The motor froze up and needs to be replaced.

However I am unsure of which direction in which to go. The outdrive (Pre-Alpha 1) is in excellent shape, was used only in fresh water, and was recently serviced with lots of parts replaced. So I would like to use this outdrive if possible.

No machine shop will rebuild my engine because they don't want to touch it due to its age. However, I found a 2.5 litre block, heads, crank, and a few other parts from someone who was storing them for decades. I had a machine shop go through and check them. Everything checks out. Now I need to acquire the rest of the parts to build a working engine.

There are plenty of Mercruiser 3.0 parts out there and not may for the 2.5. So I'm wondering what parts will work on my 2.5 , from the 3.0 ? For example, will the oil pan from a 3.0 fit on the 2.5 block ? How about the cam ? How about the crank ? Heads ? Starter ?

With regards to the exhaust manifold, I know a place (on Long Island) where I can buy a new one for a reasonable price. So that part is not a problem. But I'm wondering if I need to stick to 2.5 parts or if I can interchange some from the 3.0.

Thank you very much for any help that you may have. I have even pondered filling up the hole and putting an outboard on the boat. But that could be more trouble than its worth. I just want to cruise around the lake some more in this classic boat. Sea Rays are my favorite.
 
If you plan on keeping and using your boat you should look into if you’d be better off buying a 3.0 motor and a remanufactured alpha.

I have a 1970 2.5 that is very strong w an updated outdrive and I love it.

If, and I mean if, that 2.5 ever goes I’ll repower w a 3.0.
 

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