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2 pc rear main motor mating to Alpha Gen II

hystat

hystat

Outstanding Contributor
"I have a complete 1986 (2

"I have a complete 1986 (2 pc rear main) 4.3L bobtail engine. I would like to use it for a repower. My boat is a 1992 with 3.0LX and a Gen II drive.
Questions:
1. Are early Alpha 1 and later Gen II driveshaft splines the same? i.e. will an old style coupler engage the drive spline of a GenII? (I know I'll have to change ratios - no problem there)
2. Will I be able to use an old style Mercruiser coupler with the bellhousing from the 1992 3.0? Maybe I'll have to "clearance" it, to clear the old fashioned coupler?
3. If answer to #2 is no, then will an early bellhousing mate up to the Gen II transom plate?
tks!"
 
"Hy;
The 4.3 will mount on th

"Hy;
The 4.3 will mount on the Gen II transom assembly just fine.
The shafts are the same OD and spline count. It will fit just fine.
The 4.3 generally uses a 1.84 ratio drive. What is your drive ratio? If its 1.98 you should change it, or you could try to just make up the difference with a higher pitch prop.
You will need an exhaust Y pipe to fit onto the transom assembly as well as any other missing exhaust pieces.

Rod"
 
"Thanks again, Rod!.... fiddli

"Thanks again, Rod!.... fiddling with the prop calculator tells me that if I go to a 23P with my 1.98 ratio I'll be bang on, but it will depend if someone buying my 3.0 wants the drive or not...if they buy the drive I'll get a 1.84 from SEI.
I gave up on the 350MAG swap plan because Bayliner says this hull was never sold with an engine bigger than 4.3 and they dont know how it will handle..so I'm playing it safe...and that will keep my insurance company happy too probably"
 
"[b]"fiddling with the pro

""fiddling with the prop calculator tells me that if I go to a 23P with my 1.98 ratio I'll be bang on,"

Ayuh,....

You'll find that the prop calculator doesn't work like that...
I'm Betting you'll be up to 25" or More....Unless you regear the drive..."
 
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