1979 Merc 90 mounting question

[bc28036]

I picked up this outboard last week and with a little work I got it fired up this weekend. It is equiped with hydraulic tilt/trim and I picked up the pump, wiring, etc when I stripped the old motor off the former boat. I am going to transplant it to my current boat....a 61 whitehouse that has a 74 johnson currently on it (replacing due to poor compression on bottom cylinder). I actually have two questions when doing this.
1) I do not have any interest in using the OEM tilt/trim (don't even know if it works). I will be using a CMC unit that I picked up. How do I lock the motor down when in use? The old hydraulic system has a hydraulic lock on it but I don't know what to do now. I was planning on just taking the old rams off and running like a manual lift but i have no way to lock it when in operation.

2) I will have to move away from the factory merc steering setup (single cable) since it is too short and will be using the current dual cable manual steering currently on the boat....any problems with this idea?

 

[Chris1956]

Re: 1979 Merc 90 mounting question

OK, Are you talking about using the original equipment cable and pulley steering system? if so, that motor may be too powerful for it. I would be real careful when you test it as it could break the cable, pulley or spring and go into a tight turn at high speed and toss you (or someone) out of the boat. 50-75HP was the normal limit for those old steering systems.

On the PTT. Originally on non-PTT motors Merc had a reverse lock and two shock absorber type cylinders designed to hold the motor down under reverse use and decelleration, respectively. The PTT unit also has a reverse lock built into the PTT system. of course if you do not plan to use it, and you do not know it's condition, I am not sure what to suggest.

 

[bc28036]

Re: 1979 Merc 90 mounting question

Yep, origional two cable and pully setup on the 61 Whitehouse boat. I was worried about the power of the Merc 90 as well. I pirated the Merc steering setup from the donor boat (bass rocket type) but the steering tube/cable is too short. Do you know where to get longer replacments?

As far as the PTT goes I just don't want to dump a bunch of money into an old system when I have a newer more compact system that I know works (CMC). What if I pulled the rams off the mount and replaced them with a fixed solid rod/bar? The motor would be locked down all the time. The only problem I see with that is if I strike something with the foot while at speed. The motor will not be able to move up and likely it and my transom will be taking a swim. Correct?

What is the likelyhood of retrofitting a manual transom from an older I6 motor. Will it make any difference what the HP level is as long as it an I6. BTW I have been looking to see if any manual transom mounts are out there but haven't had any luck.....any sources that you all know of for parts.

 

[Chris1956]

Re: 1979 Merc 90 mounting question

Steering cables are sometimes available. You need to know what brand of steering it is. A lot of time you need to buy helm and cable together. Cheap rack and pinon steering is fine on that boat.

Does the CMC PTT allow motor to kick up if you hit something? If so, the solid rod idea is OK. You can also get manual lock down parts from a salvage yard. any inline 4/6 motor from the 70s to 90s will fit I would think. You need a plastic cam that fits on the shift rod (you may already have one installed), the vertical locking rod, the horizontal lock rod, and a couple of springs. Also you will need the original shocks to replace the PTT cylinders and brackets.

 

[bc28036]

Re: 1979 Merc 90 mounting question

Update: The CMC PTT does not allow for kick up. I just found a manual 73' TT from a Merc 50. Can anyone tell me for sure if it will fit/work on my 79' Merc 90 I6. I just hate to plunk down cash and it won't fit/work.

 

[Chris1956]

Re: 1979 Merc 90 mounting question

I do not think that PTT unit will fit, sorry. One from an 80-150HP inline motor from the 70s will fit.

You might revisit the manual lock down idea. that will work adequately I would think.

 

[bc28036]

Re: 1979 Merc 90 mounting question

I am just concerned about striking an object if I have the motor locked all the time. I don't want to have my motor an transom take a drink. I have located another manual TT from a 67' 95 hp I6. I believe this will fit since it is just an earlier generation of my current motor.....what is your opinion?

 

[Chris1956]

Re: 1979 Merc 90 mounting question

I have to give you a resounding "I don't know" on that question. Can you go see it or have the guy send a picture of it? Your PTT system will have two upper trim cylinder brackets, the two trim cylinders, 4 hydraulic lines (2 large, 2 small), and a trim pump/resevoir combo. It will also have a wiring harness and three button panel.