Tilt & Trim 1979 mercury outboard 90hp

[brokedown]

My tilt and trim is not working properly. at first i could not get the motor to raise up. The oil level in the resivor was 1/4 full so i toped it off with 30w motor oil. Now i can get it to go up and down but when i trim it up the motor will slowly fall back down on it own. any ideas??

 

[KDT1961]

Re: Tilt & Trim 1979 mercury outboard 90hp

My tilt and trim is not working properly. at first i could not get the motor to raise up. The oil level in the resivor was 1/4 full so i toped it off with 30w motor oil. Now i can get it to go up and down but when i trim it up the motor will slowly fall back down on it own. any ideas??

Use tilt and trim hydraulic fluid (you can buy it at Wal-Mart) instead of motor oil.

 

[brokedown]

Re: Tilt & Trim 1979 mercury outboard 90hp

Thanks for your help i will change it tonight. I still cant see why the motor would fall back down even with the current oil i have in there. How do you change out the fluid? I can pump the fluid out of the resivor but how do i get the fluid out of the pistons.

 

[arsenalpsu]

Re: Tilt & Trim 1979 mercury outboard 90hp

I'd bleed they system first to make sure there is no air in it then refill the oil. Also, the 30w oil you put in, I hope you used the non detergent oil, like chain saw oil. The chemicals in traditional car oil can eat away at the rubber in your system. I'd use steering or hydraulic fluid.

Here are a few other ideas:
Are there any exterior leaks? If so you could need new o-rings in your tilt ram. You could have crap in your check vales too. Check the o-rings on your manual release valve.

For your sake I hope it?s air in the system or else you?ll have to start talking it apart.

 

[Chris1956]

Re: Tilt & Trim 1979 mercury outboard 90hp

Broke, The other posters do not have experience with your PTT unit. They have given general advice, which works for a lot of PTT units, however is not as applicable to your unit.

Your PTT unit originally called for standard detergent 5W-30 motor oil. someone over the years may have used auto trans fluid in it. This is acceptable, however, you do not want to mix them, so check what you have. I would drain the SAE- 30 oil out, since it is too thick to work properly.

You can invert the pump/resevoir unit and let the oil drain out. Refill with 5W-30 or any ATF.

The pump is self bleeding, but the cylinders must be bled manually.

If the cylinders are leaking down, is it likely due to either bad teflon piston seals or a bad control valve. Usually it is the teflon seal.

There may be rebuild kits for the trim cylinders, which include a bunch of Orings and the teflon seal, however, instaling the teflon seal is tricky, and requires a special tool like a ring compressor to get it back into the cylinder liner.

 

[brokedown]

Re: Tilt & Trim 1979 mercury outboard 90hp

how do i go about bleeding the system. I don't know if this helps but just last week everything worked fine. When i turn the manual release the t&t runs but does not move the motor i think this means it is working correctly. i Cant find any leaks.

 

[brokedown]

Re: Tilt & Trim 1979 mercury outboard 90hp

thanks for everyones help. there are two pistons controlling the tilt and trim they no doubt should be looked at due to the age of the boat. but i have a felling the one piston could keep the motor from falling which leads me believe it is a control valve or a check valve i am not sure what it is called. First were are the valves and what should i look for.

 

[Chris1956]

Re: Tilt & Trim 1979 mercury outboard 90hp

Broke, The trim cylinders are conected together. If a seal fails in one cylinder, the motor will slowly lose trim.

The control valve bolts to the bottom of the pump. The hydraulic hoses are connected to the control valve. The manual release will allow you to tilt the motor up and down using your muscle. If you have pumped the motor up electrically, opening the manual release will not allow the motor to go down.

Each trim cylinder has two bleed screws. The down bleed screw is on the top of the trim cylinder. The up bleed screw is located on the trim cylinders, near where the hoses bolt on. Each screw must face up to bleed the cylinder, so in order to bleed the up circuit, the trim cylinders need to be removed from the motor and turned to face the bleed screw up. Run the trim pump to bleed the cylinders. Wait for pure oil (no air) to be expelled.

 

[brokedown]

Re: Tilt & Trim 1979 mercury outboard 90hp

there are 4 screws on the 1 cylinder on the top there is a flat head screw and a hex head screw and the same setup on the side of the cylinder were the hoses come in. which are the bleed screws? There looks like there are 2 control valves one valve there is 2 fat hoses one for each cylinder and on the other valve there are 2 skinny hoses one for each cylinder. i guess my question is what is the function of each hose. I need to send you a check for all of you help thanks.

 

[Chris1956]

Re: Tilt & Trim 1979 mercury outboard 90hp

The flat head screws are the bleed screws. One hose on each cylinder makes it go up, the other down. I will guess the fat hoses are for down.

 

[brokedown]

Re: Tilt & Trim 1979 mercury outboard 90hp

Do i need to bleed both cylinders at the same time? how does my manual release valve need to be set?