Hi all, I'm new here. Bought a...

[Dee]

Hi all, I'm new here. Bought a 1990 27 Sundancer that was sitting on land for 7 years. We are replacing all the wiring as quite a few things are inoperational. But, my main problem is the Merc Alpha outdrive (7.4L 330) When the tach reaches 3000 the drive shoots up out of the water. Runs fine otherwise.  I thought it was because the trim tabs weren't working but I've been told that wouldn't be the reason. Anyone know why this may be happening? Thanks very much for any help! Debra 

[wingless]

Welcome.

Good luck e/ your boat.

The problem as-described doesn't make sense.

The hydraulic rams will lift or lower the drive on-command.

If the linkage was broken, then forward thrust at 3,000 rpm would push the drive down, against the transom, not up out of the water.

IMO, the only way for the drive to lift out of the water during forward propulsion is for the hydraulic rams to lift, for the pump to be active causing the hydraulic to lift.

FYI, the hydraulic outdrive lift is different than the trim tab hydraulic actuator.

My suggestion is to examine the wiring, switch, from the power source to the hydraulic pump. Look for degradation. Wiggle and tap on the parts while the circuit is powered to determine if the fault can be reproduced.

For the rewiring project. Use only marine-grade wires of sufficient gauge throughout the boat. Marine wire has individually tinned conductor strands and has appropriate insulation rating and resistance. Even though the cost is higher, I like Ancor brand.

Use marine-grade terminals of appropriate size. Use a high-quality ratcheting double crimp tool. For the larger battery cables I like the TMB6 tool w/ appropriate dies.

Follow the marine color code. Create an accurate wiring diagram. Label both ends of every conductor, I like my Brady printer on heat shrink or self-laminating cable labels. Follow ABYC throughout. Use chafe protection, like split loom or raceways. Support the wiring every foot, w/ cushioned stainless Adel clamps or nylon wire ties w/ anchor holes.

Use only marine fuses, circuit breakers, switches and lights.

Feel free to ask questions as you go.


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http://www.sterndrive.info/sitebuildercontent/sitebuilderpictures/Mercruiser-Alpha-1-Gen-2-Trim-Cylinder-Parts.jpg

[Captain_Clark]

Hi, sounds like maybe at 3000, your engine is producing so much torque, that a pressure relief valve might be popping open in the hydraulics, or maybe bypassing fluid inside the hydraulic cylinders…?

[Stu2]

I purchased a 1994 270 Sundancer a year ago as a project boat and had a lot of problems with the trim system . If your drive is coming up while in forward I would suggest you disconect the power lead going to the trim pump. Torque normally pushes the drive in or down in forward..the trim limit switch and the trim indicater switch can cause all kinds of problems if broken,wired wrong or if the two switches wires are crossed. The switches look alike but they are different,.
Stuart corenblum