72' Merc. 115hp Trim Problem

[Meat Stick]

I have a 1972 115hp Mercury that is having trim problems (2 side mounted cyl./1 pump). I just replaced the o-rings and seals in the trim pump/control valve. The trim works very well both up and down, until it is in the full up position then the trim motor runs but will not move the outboard even with help. I initially thought that this was air in the system and bled it from both of the bleeder screws on the top and bottom of each cyl. (8 total). When I loosened the lower bleeder screw on the bottom of the right cyl. the outboard lowered. I raised and lowered the motor many times without flaw, taking care not to go to the full up position. When I did raise it to the full up position, it did it again. So, I figured I would try adjusting the tilt limit switch/bolt (only on starboard cylinder, port cylinder screw and bolt missing for what looks like a long time), this did absolutely nothing. By the looking at the tilt limit bolt, screw, and bracket I don't understand how it works, but I tried what the SELOC manual said and turned it counterclockwise to no avail. I even fabricated a stop collar for the cylinder so that it would not tilt to full up. When I did this it trimmed to the collar, then behaved just as it did when full up, and I had to release it by bleeding it off again. I would appreciate any help.
Thanks,
Chad

 

[Chris1956]

Re: 72' Merc. 115hp Trim Problem

Chad, I am not sure what your issue is. The PTT system will raise that motor until the pistons are fully retracted, but no more. You can then pull it up and latch it, by hand. There is only one trim limit switch, and it stops the pump from running, after the trim has exceeded the adjustment.

The bleed screws are slotted stainless screws, and a total of 2 per cylinder. One is next to the zerc on top of the cylinder. The other next to where the hydraulic lines attach. The pump is self bleeding.

 

[Meat Stick]

Re: 72' Merc. 115hp Trim Problem

Chad, I am not sure what your issue is. The PTT system will raise that motor until the pistons are fully retracted, but no more. You can then pull it up and latch it, by hand. There is only one trim limit switch, and it stops the pump from running, after the trim has exceeded the adjustment.

The bleed screws are slotted stainless screws, and a total of 2 per cylinder. One is next to the zerc on top of the cylinder. The other next to where the hydraulic lines attach. The pump is self bleeding.

When the pistons are fully retracted (outboard is full up) it is as if it is locked in the up position and will not lower. Once the bleeder screw on bottom of starboard cyl.(slotted screw (you are correct 2 per cyl.) not the allen head screw next to it, I was counting the allen screws on my 8 count) is loosened and trim oil comes out, the outboard will lower. Then it works fine up and down, until raised to full up then it will not lower.

I cannot pull the motor up and latch it by hand to answer your question.

I thought that the pump was self bleeding with the vent next to the fill hole but was not sure, thank you for that info.

If you have any more questions let me know, I'll try to answer them.

Thanks for the reply,
Chad

 

[monk-monk]

Re: 72' Merc. 115hp Trim Problem

Tell me more about the o-rings and seals you replaced...There is 8 o-rings...4 on each side of the "manifold plate"...(the flat piece between the pump body and the control valve)...BUT what seals did you change, did you disassemble the control valve itself..where the check balls and springs are located..?

 

[Meat Stick]

Re: 72' Merc. 115hp Trim Problem

Tell me more about the o-rings and seals you replaced...There is 8 o-rings...4 on each side of the "manifold plate"...(the flat piece between the pump body and the control valve)...BUT what seals did you change, did you disassemble the control valve itself..where the check balls and springs are located..?

Yes, I did replace the 8 orings, but did not disassemble the control valve itself. I could'nt find an exploded diagram of the control valve and did not want to open up a can of worms that I had never seen before. Is it fairly simple to take apart to examine, or are there adjustments that I could try to cure the problem?

I took some pictures (should be able to click on them to make them bigger)of the trim cylinders I was talking about, because I am more of a visual guy myself and I thought it might help. If there is anything else you would like me to take a picture of for visual reference let me know if it would help.

Starboard side with the trim limiter bolt/bracket.


Port side with out the bolt/bracket.


Here is the bleeder screw (slotted one not the hex head) on the bottom of the starboard cyl. I used to lower the outboard after it would not move from the full up position.

Thanks,
Chad

 

[75TowerOfPower]

Re: 72' Merc. 115hp Trim Problem

So what if you don't go all the way to the "full-up" position? Will it come down like normal? I think your pump should have the vent knob on the pump side of things. It will allow you to lower the unit with out using the screws on the cylinders. So there is a poissbility that there is still some air in the cylinder since when air pushing against air nothing really happens compared to hydro fluid pushing against hydro fluid. SO you have have a tad of air in there.

 

[Meat Stick]

Re: 72' Merc. 115hp Trim Problem

So what if you don't go all the way to the "full-up" position? Will it come down like normal? I think your pump should have the vent knob on the pump side of things. It will allow you to lower the unit with out using the screws on the cylinders. So there is a poissbility that there is still some air in the cylinder since when air pushing against air nothing really happens compared to hydro fluid pushing against hydro fluid. SO you have have a tad of air in there.

It works great as long as I don't go allow to go to full up (or stop at the collar that we fabricated), so yes it will come down like normal. I don't believe that my pump has the bleeder, it just has a vent screw that I have loosened and tightened while stuck in the full up position to no avail. I don't think that I have air in the system because when I bleed the cyl. back down there are no bubbles or gas pockets, the fluid just flows out.

Thanks for the suggestions though,
Chad