Front motor mount setup on most large aluminum boats with GM 4.3L V6

havoc_squad

Senior Chief Petty Officer
Joined
Mar 5, 2011
Messages
739
I'm curious, what does the typical aluminum boat aluminum stringer support setup look like for the front motor mounts of boats like the Starcraft Islander 21 footers with the GM 4.3L V6 engines?

I may have the opportunity to get a fair market priced or better 1970s Starcraft islander or Crestliner's nordic aluminum cuddy in good condition running the GM straight inline 6 with that era's 1970's Mercruiser MR drive.

I would like to have a clear view of what would be needed to retrofit enough structural support for the front motor mounts to upgrade it to put a GM 4.3L V6 vortec with an Alpha One Gen 2 V6 dressing package from a cheap donor boat.

The reason behind it simply is parts support concerns over the long term and aluminum cuddies with full legal ownership paperwork are rare as hen's teeth around here, especially so for ones that mount outboard motors. You're just not going to find newer ones around here unless they want $10k and above which few will actually buy.

Replacement parts is easier to get for Alpha One Gen 2 and easier to get replacement 4.3L V6 vortec engines and parts than that inline 6.

I'm sure a lot of the details involve securing it so the torque of the motor doesn't warp the motor mounts that get bolted to the aluminum stringer supports and cause alignment issues.

I'm curious if it would cost just as much to reinforce for the GM V6 engine front motor mounts as it would to reinforce for an outboard bracket closing off the outdrive hole.
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,103
Ayuh,...... I can tell ya what I did, when I pulled the 3.0l outa my ole '74 Starcraft Islander, 'n dropped in a 4.3LX / Alpha 1,....

Stringers, bulkheads, 'n inside ribs were 'bout .063", bend to shape,....

So, I cut a piece of .090" aluminum 'n bent it into sorta a shape that gave me a shelf, top of stringer, wide enough to catch the motor's mounts, 'n then bent down to rivet into the base of each rib,.....

Then I skeletonized it as much as I dared, for service access to everything else in the installation,....

Riveted to the top of the stringers, 'n to each rib at the bottom, it never moved in over 20 years,.....

I used plywood blocks for final elevation to the motor's adjustable mounts,...
 
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