aq125 hull flex?

[jaknight]

I have a sunbird bowrider with a volvo aq125a / 270 setup. When I am out on the water I notice quite a bit of movement in the motor. It seems like a lot but its really the front of the motor moving up and down only maybe 1/2 - 1 inch. I found tons of threads about outboards saying they should not move at all. But this is a 4 cylinder inboard hanging out from the hull with no other support. The gelcoat is fine and with all my weight on the outdrive I can not really see any flexing in the hull itself. It looks maybe more like the mount is shifting.

How much flex is too much with this thing? Has anyone ever added a front motor mount to remove some of the stress from the hull?

 

[Bondo]

Ayuh,.... Welcome Aboard,.... Odds are 99 to 1 that yer transom is rotten, causin' the movement,.....

 

[dennis461]

The bondo may be right regarding transom.
There is another possibility.
The bellhousing sticks through the hull and is held in by a clamoing ring and two large rubber o-rings.
The weight of the motor is on a rubber stud under the bell housing just above your drain plug.
The rubber stud prevents the motor from spinning (opposie of prop rotation).
Almost impossible to see these things.

I assume you do not have any motor mounts in the boat.

Now, rubber can get old and loose.
IF, that's IF the transom is not flexing, then you rubber mounting system could need repair.

On my boat, I added two from engine mounts (motor seemed to jump up around 4 inches)'
The motor mounts will not fix the transom, but I think my boat is stronger than before and has not broken in half in the ocean.

 

[jaknight]

This movement is minimal. I think it may be a mix of the two. There is defiantly flex in the transom, but only at the top, and maybe 1/8 of an inch in the center. How did you attach front motor mounts? Do you have any pictures? I am more worried about the force of the motor bouncing down then the stress of running the boat. On smooth water the engine seems pretty still.

 

[jerryjerry05]

By all means put in a motor mount of some kind.
It will stop the flex and future damage.

The transom on Sunbirds were never that good anyway.
The Sunbirds were a direct competition boat made to compete with Bayliners and their cost.
My opinion was SB was even cheaper made.
The company I worked for sold SB and BL and the quality of the SB was lacking.

The Volvo was the good part of both boats.

 

[jaknight]

I have pulled every screw going into the transom and removed and resealed the drain. There was no moisture anywhere. Someone used non stainless screws which were rusty outside but clean as new inside.

Where on the motor could I mount a mount?

 

[PiratePast40]

Do a search for Volvo B230 motor mounts to get an idea of what they look like and the mounting bolt holes in the block. Then get the mounting brackets from a boneyard, ebay, or make them yourself. You then need to make a mounting point inside your engine compartment and glass it in or seal it some other way. You could lag bolt the lower mounting bracket to the engine compartment and then bolt up the rubber mount to that. You really don't need the factory mount. Something home made can work just as well, and the snubber can be anything that works.

 

[dennis461]

looking under port side, from front.

I used a square block of wood (engineered wood) fiberglass covered. then glassed it to hull bottom and stringer.
Both sides.
galvanized hat channel (street sign post) from port to starboard.

picture is a stock automobile mount
other side I did not have an auto part, used industrial machine vibration isolator snubber

 

[dennis461]

starboard side