OMC 2.5l stringer vs Mercruiser 3.0l

[Optimax89]

Hey All
ill start with introducing myself
im Marc, almost 30 years young and i live in the Netherlands, i am a car mechanic at a Renault dealership and used to be on the water all my life

recently ive bought myself a Allmarine 485 with an 120hp 2.5l GM “iron duke” engine which is connected to an stringer drive ( the later type, the lower casing doesnt look like a bullet )

the previous owner said that the 2.5 needs to be rebuild, and has already started with taking the engine appart ( i asked him why the engine needs to be rebuild but he couldnt aswer my question )

now my “problem”
i cant find any decent replacement engines in the Netherlands, but ive found a 140hp 3.0 mercruiser which looks like the 2.5 i have ( the seller said that the engine was used with an omc stringer and that drive comes with the sale )
the difference with the drives is that this one looks like a bullet so is an eary type i guess

are the omc 2.5 and mercruiser 3.0 changeable? Ive read something about a 1pc and a 2pc rear seal?? Is it possible to see what seal i now have without pulling the engine out off my boat?

sorry for my “bad” english i dont use google translate or any other translating programms

for the people who can give me some advice, can it be written down in simple english?
Thanks in advance

marc

 

[kenny nunez]

If both engines have the 2 piece rear main seal then all of the external parts will work on both engines. The only main difference between the 2.5 and 3.0 is the piston size, cylinder head and manifold.
If the “bullet” style lower unit has electric wires then it was made until 1977. After 1978 all OMC drives were mechanical shift. Try to post some pictures . 1 piece style engines have a smaller bolt pattern for the flywheel.

 

[Optimax89]

Thanks for your answer
asap im home ( im on holliday now ) ill get some pictures

and if the 3.0 is a 2pc seal and the 2.5 is a 1pc can i switch the cranks? If the 3.0 fits its gonna get rebuild anyway

 

[kenny nunez]

The bore where the rear main seal is located is different between the 1 pc and the 2 pc blocks. The 3.0 would be the better engine to rebuild over the 2.5. I must apologize that I forgot to mention that the 3.0 has a 4” bore and 3.6” stroke. The 2.5 is 3.875” bore and 3.25” stroke. By the way, Merry Christmas!
There was a movie filmed in your area some years ago. “Puppet On a Chain” that has a boat chase scene that was really good.