1984 Mercury Trim Question

[MNhunter1]

Picked up a new project with a 1984 70hp Mercury hanging off the back with trim and an external (in the boat) pump. A bit different than the integrated trim I had on my 1987 Classic Fifty and 1987 35hp. What is the consensus on these trim units? Worth holding onto, or am I better off looking for something different, a CMC unit?
Looks like it requires a few more holes in the transom I’ll be rebuilding/replacing and takes up more space under the splashwell for the pump. Hull is also rated for up to 115hp, so not sure if I’ll be looking to upgrade down the road, but the hull is light enough that the 70hp should be more than adequate for my needs.

 

[Alumarine]

Those tilt/trim systems work well.

 

[Chris1956]

The advantage of those trim systems, is that there is no limit to which you can trim them under full throttle. Newer units have a hard limit for trim.

However, you need to be careful that you do not trim them where the water inlet sucks air. usually the prop will ventilate before that happens.

I found that the trim cylinders often leak at the trim rod. However, new orings can be easily installed. You might source new orings, against that day. A service manual will identify the oring dimentions.

 

[MNhunter1]

Thanks! Is this what one would refer to as a dual or twin rod system? Are there different version used across the 70's and early 80's, or were they basically pretty standard?

My biggest dilemma is whether its worth punching additional holes through a new transom if I were eventually to upgrade down the road/mindful of the fact the extra holes would no longer be used/need to be filled.

 

[racerone]

That system was used for a number of years.------Bonus is that the pump / motor is safely out of the elements inside the boat.-----Nothing wrong with this unit.

 

[BWR1953]

That's the same unit I have on my 1985 Mercury 50HP 2-stroke. It works well.

I also have a pair of 70HP Mercs with the exact same setup which I'll use on my Chieftain.

My throttle control handle has 2 switches, one is used during trimming and the other is used for raising to trailering height. When I added a bow mounted trim switch, I just used one switch, wired directly at the pump. That allows me to completely raise the motor when I'm up front, whether fishing or otherwise.

 

[racerone]

That system was also used on the 4 cylinder 50 and 4 cylinder 80/ 85 models.----Used on the inline 6 cylinder to 150 HP.----Nothing wrong with that system either.

 

[MNhunter1]

When I pull this motor off the boat, does it come off as one unit, or does the motor and tilt unit get removed/installed independent of one another?

 

[Chris1956]

The trim brackets should be bolted to the transom clamp, so the engine and trim cylinders can come off as a unit. However, that requires that you unbolt the hydraulic lines. You would need to bleed them upon reinstall. The threads where the hydraulic lines connect to the trim cylinders strip out easily. That is a weakness of the system.

Alternatively you would unbolt the trim cylinders and remove them, prior to pulling the engine off the transom.

 

[racerone]

The decals in the pictures ( post #1 ) are not for an 84 model.

 

[MNhunter1]

The decals in the pictures ( post #1 ) are not for an 84 model.

Yeah, based on the serial number, it looks to be an ‘82. The hull is a ‘84, so I believe the PO believed the motor to be the same.

The trim brackets should be bolted to the transom clamp, so the engine and trim cylinders can come off as a unit. However, that requires that you unbolt the hydraulic lines. You would need to bleed them upon reinstall. The threads where the hydraulic lines connect to the trim cylinders strip out easily. That is a weakness of the system.

Alternatively you would unbolt the trim cylinders and remove them, prior to pulling the engine off the transom.

Thanks! I’ll be stripping everything off the hull for a complete rebuild and placing the motor on a stand to go through it as well. Was hoping I could just transfer it as a complete unit, which it sounds like I can. I’ll be mindful of the threads

 

[BWR1953]

When I pull this motor off the boat, does it come off as one unit, or does the motor and tilt unit get removed/installed independent of one another?

Yep, it comes off as one unit. Make sure that you take extra care to not let the pump fall. Mine fell and pranged the top of the pump to the point that it was inoperable. Doh. You can see it resting on the bottom of the shop crane in the pic. It fell over and landed on the top of the pump, which dented, preventing the motor from turning.

Fortunately, I had a spare and got it installed and running with no issues.

The pump is self bleeding, which is a nice feature. Top it off or fill it up and it'll do it's own thing.