1971 Mercruiser 120 Questions

I became the proud owner last fall of a Mercruiser 120 powered trihull, it's appears to be in excellent condition, but hasn't been run in at least 5 years.
I did a few basic checks and the motor looks like it will be fine, it's got good spark, the fuel was treated and the cooling system has traces of antifreeze being pumped through it and let sit, so I don't think anything would have any freeze damage.
The prop was off and the shaft coated in heavy grease, there are reciepts for a new impeller and housing, new prop, new steering teleflex, and a new control cable.

The battery is shot, but I have a good used car battery in it for now for testing, I notice one problem right away, the outdrive will power down, but not up, I can jump out the solenoid at the pump to bring it up, as I did for towing. It stays up with no problem, and hasn't dropped any all winter sitting in my garage.

My question is, what should I be looking for when reviving this for use this year? It's had been sitting outdoors when I found it, but looked to be pretty well covered, so cosmetically it's in good shape.

My concern is with the I/O unit, I have never owned a boat with an I/O. Is there anything I need to check or replace before I put this in the water? I will obviously change the lower unit lube, but was reading here about bellows problems and other seals, and have heard horror stories about bearing failures in these.

I have owned outboards and pure inboards before, and had one early Evinrude Sterndrive boat that had a boot that surrounded the entire drive, this looks much different than that set up.

My main concern is not to do any damage by putting it in the water and finding later that some rubber part was dryrotted and leaking. Is there anything I need to check or should I just lauch it and see? I don't want to be at a busy boat ramp with a problem or a sinking boat.

Any suggestions?

Re: 1971 Mercruiser 120 Questions

I would replace the impleller in the lower unit even if it looks good - requires draining the gear oil replace seals around drain and vent screws. Check the belt and the bellows for any signs of dry rot or cracking - if you see any replace them and inspect u-joints and gimbel bearing before running. I would replace the fuel and engine oil if it is more than 6 months old. also replace fuel filters. I would also pull spark plugs and put a little oil in each cylinder if it has not run in over a year. Your problem with the outdrive rasing and lowering may just be a lack of fluid in the trim motor resivoir or a bad selenoid. Start it out of the water with the muffs on before putting in - listen for any strange noises or loud valve tap, check oil pressure and charge from alternator - if it idles good and revs good then think about putting it in the water. After running for a couple of hours in the water drain a little of the gear oil and if it looks milky/discolored or you see metal shavings in it then you have some problems. I own a '78 120 merc that had sat for many years before I bought it. Had to do a lot of work that was past due (exhaust manifold, risers and bellows) but the motor and gears were all in good shape.

Re: 1971 Mercruiser 120 Questions

The manifold and heat riser is new, and it don't show any signs of heat at all. How much work is it to change the bellows and any other seals?
I was told by a local marina that these drives had a problem with bearings and u joints. I guess they were talking about the gimble bearing?
The good part is that this thing is super clean, it looks new. The engine has no paint loss, no grease or oil spots or leaks, and the outdrive looks mint, but the lower unit has a lot of paint loss, it doesn't match the top casting appearance wise.
The former owner had been rebuilding this one piece at a time, but dumped it during a divorce.
They had also replaced all the seats, new floors were installed by a local marina there, new rubber floor covering, and all new wiring, he had hunted down an oem wiring harness for the boat. I don't think the last owner did any work himself, I have a huge stack of receipts from 1997 to 2000, and 2000 was the date on the battery that came with it.

The solenoid works, I jumped power to it from the battery to run the drive up to tow it home. It's either some sort of safety or a bad switch. It seems to try to go down even when I push the trim button or trailer button. The trim buttons are all part of the dash console, the whole steering wheel, speedo, and back plate are all one large chrome or stainless plate that says Mercruiser, the button assembly is part of that. The old owner said it worked when it was last used. Is there a limit or safety switch somewhere that may be stuck? If I jump the solenoid and leave the drive about midway, and then hit the button, no matter which button I hit, the drive goes down, even the up or trailer buttons run the drive down.
How do these buttons work, do they switch polarity fo up and down? Or is that done at the solenoid? (When you refer to the solenoid I assume you mean the large 30amp starter type solenoid on the pump, right?)

Would running it with the muffs show any into the hull leaks if the bellows are bad?
What are the signs of a bellows leak? Would I have a gear oil and water mix or a leak into the hull?

Re: 1971 Mercruiser 120 Questions

Would running it with the muffs show any into the hull leaks if the bellows are bad?

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i'm not the pro, but don't think it would. it'd only show leaks of the cooling system. from water pickup, thru the hose leading up to the transom shield, thru the transom shield, and hose up to t-stat. thru the engine, out the exhust manifold and riser, down to the exhust elbow, and out thru the exhust bellows down to exiting thru the prop...might show exhust bellows leak, but don't thik that's of much relivance. nothin to do with the (drive shaft) bellows.

What are the signs of a bellows leak?

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water in gear lub. howlin gimble brg. water leakin into the inside of yer boat right where the drive shaft is, clunkin u-joints perhaps....i'd think there'd be more, but like i said, i aint the pro here......just my guesses........

sounds like ya got's a nice rig.... got pics?

Re: 1971 Mercruiser 120 Questions

^ziggy is correct you will not be able to tell if you have a bellow leak by running it on the muffs. Just inspect bellows closely before putting in water. After running you can pull the drive and look for water inside of them- that is the only real way to tell. As for the trim - mine had the same problem initially - went down but not up. Top fluid off first. Next had a friend lift up on it while I hit and released switches. If yours is set up like mine you have to hit the middle button labeled trailer and the up button at the same time. My trim limiter switch was not hooked up to just hitting the trim up switch did nothing until I hit it at the same time as the trailer switch. I think mine had water/condensation or a vacuum lock at first. After my fiend lifted up on it and I ran it up and down a couple of times everything worked fine (except the trim limiter which had to be rewired) The selenoid is what you referred to - looks just like an auto selenoid. But start simple and work your way up. If selenoid checks out then look at wiring. I do not know of any safety switches in the system - just the trim limiter which prevents you from trimming up to far which damages the u-joints if you are running.

Re: 1971 Mercruiser 120 Questions

sabastianunf, my switches are labeled with instructions to hit both upper buttons to raise beyond running point for trailering, neither that nor the up button actuate either the solenoid or the motor, if I jump the terminals across the solenoid, I can power it up, nothing happens if I simply jump power to the small terminal of the solenoid, but the solenoid clicks, as it does when the down button is pressed and the pump runs and the unit lowers. The solenoid works, but when the solenoid is actuated, the motor only goes down. There has to be something that either reverses the direction either electronically or by changing the valving of the pump? It seems like the pump only wants to go down, and the voltage signal is the same fat the solenoid no matter which button I press.

If the bellows were to leak, whats the first symtom?
Will it cause the boat to sink or just cause shaft, ujoint or bearing damage? My main concern is putting this in the water and having it take on water faster than the bilge pump can pump it out.
It actually don't look like that area will be below the water line? The waterline or stain on the side of the boat at the rear is ony a tad higher than the prop itself, which in that case the pivot point and upper drive unit will be well out of the water at rest? In other words, it's not likely to leak any water anywhere around the drive or gaskets without the engine running or the boat moving or under hard deceleration? The prop is about 1" lower than the lowest point of the hull.
The gear lube is clean now, but there's a bitt of oil wetness behind the prop, the unit was full, and it don't drip on he floor.
What is involved in changing that seal?

Re: 1971 Mercruiser 120 Questions

sabastianunf said:

^ziggy is correct you will not be able to tell if you have a bellow leak by running it on the muffs. Just inspect bellows closely before putting in water. After running you can pull the drive and look for water inside of them- that is the only real way to tell. As for the trim - mine had the same problem initially - went down but not up. Top fluid off first. Next had a friend lift up on it while I hit and released switches. If yours is set up like mine you have to hit the middle button labeled trailer and the up button at the same time. My trim limiter switch was not hooked up to just hitting the trim up switch did nothing until I hit it at the same time as the trailer switch. I think mine had water/condensation or a vacuum lock at first. After my fiend lifted up on it and I ran it up and down a couple of times everything worked fine (except the trim limiter which had to be rewired) The selenoid is what you referred to - looks just like an auto selenoid. But start simple and work your way up. If selenoid checks out then look at wiring. I do not know of any safety switches in the system - just the trim limiter which prevents you from trimming up to far which damages the u-joints if you are running.

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Re: 1971 Mercruiser 120 Questions

three wires coming out of the pump: one is grn/wh and bl/wh and blk-grnd. Black is ground at silanoid while bl wh is hot for silanoid or battery+, the other reverses the DC mtr and goes to a terminal at pump base then up to silanoid. Try using two separate jumpers/one at a time: silanoid to Battery +(be careful of polarity) and other at pump base wire terminal to battery positive. Reversing polarity will drive pump or down depending on which button is pressed. You either have corrosion on the wires as I did due to thermal aging or a bad switch at console but doubtful. definately refill pump reservoir and purge air from up/down cylinders on trim by loosining the 3/8 cylinder hose one at a time just enough to let out air to purge the system of air bubbles. after a few times up and down they self purge. Could be electrical or hydrolic in problem or as described above both which can be confusing.
PS: does SEAMan have a schematic on how he bypassed the trim until a permanent fix was done on trim sender? I'm using Jumpers which is not a good idea to to gas fumes and spark potential!!

Re: 1971 Mercruiser 120 Questions

^correct again follow this advice. I think bad switch is doubtfull as well - mine is original and has had a hard life but still works. First sign of bellows leak is water inside of bellows. You will not sink but if you destroy your U-joints you will not be going anywhere and if your gimble bearing falls apart then you can do alot of expesive damage. Bellows may be above the water line but water still gets inside - usually when you get out of throttle the wake will push up around them (visually inspect first, then run in water, then pull drive.) I wouldn't worry about replacing any seals in lower unit unless you see water in gear oil. Gear oil may be clean now but may have been and probably was replaced before storage. If gear oil discolors after running in water then look for leaky seals using pressure/vaccum tests. My problem was my trim limiter and I did not bypass - I just trimed up a little using trailering function and made sure I didn't over trim.

Re: 1971 Mercruiser 120 Questions

The trim motor runs and reverses when actuated by jumper wires. Nothing I do at the switches actuates the up function. The solenoid works as it clicks and functions in the down position, If the drive is up or partly up, if I hit either up or trailer, it still goes down. All buttons have the same function.
What is the function of the trim sender and where is it? I don't see any limit switches on the outside of the boat?

I think I'll feel better knowing that all of the bellows are new, and I can see some seapage at the output shaft behind the prop, so I think that seal should be changed. Is that seal an easy fix or major disassembly? How do I do a vacuum test on the unit?

Re: 1971 Mercruiser 120 Questions

power trim troubleshooting, will not trim up...

mechanical

improperly adj. rev. lock valve,
unit not in neutral or fwd.
drive houseing interference with gimbal ring or tilt pin

eletrical

limit sw. open or disconnected
defective push button or rocker switch
defective trim motor solinoid
proper switch not operated

hydraulic

oil level low
external leaks (fittings and parts leak)
internal cylinder leaks
too low or no pump pressure
reverse lock valve inop
internal resistance in cylinders

the limit sw. it a push button on top of the drive on the outside. look on the top of the gimble ring. the trim sender is a big tubular thing witha shaft comeing out of it mounted inside the boat. it's large...

sounds like yer really gettin into yer rig. have ya got yer oem service manual for it. it's a nesseary tool. the info i provided comes right out of the book for troubleshooting trim systems......

Re: 1971 Mercruiser 120 Questions

I don't see any limit switches on the outside of the boat?
The trimshut off switch is on the transom shield, above the gimbal ring....
It is actuated when the bell housing closes it in the 'full up' position......
I think I'll feel better knowing that all of the bellows are new, and I can see some seapage at the output shaft behind the prop, so I think that seal should be changed. Is that seal an easy fix or major disassembly?
Have you drained the drive & inspected the gear lube?

How do I do a vacuum test on the unit?
Actually you need to pressure test the drive....
The seals are designed to hold pressure, not vacuum.....

You need to get Merc. manual #1.....
They pop up on ebay, now & then.....

One other thing, a bad ujoint bellows can sink your boat.........

Re: 1971 Mercruiser 120 Questions

I ordered a CD manual, I got a Clymer manual with the boat, but it's vague and don't show me any pics. It covers too many years.
I am not 100% certain which model I have? The boat is a 1971 and I know it's a Mercruiser 120 with hydraulic tilt/trim.
Are all of the "120" drives the same? It seems there's an early one with the old motor and a later one with a newer GM motor? The paper manual I have ranges from 1964 to 1985.

My guess is that what ever is wrong, it's something caused by time or something stuck from non use. My impression of the former owner is that he had all work done by a dealer. I didn't realize that it had to be in Fwd or Neutral, but I know it was in neutral, I didn't try it in forward. SInce I when I hit the up or trailer buttons, the solenoid does react and run the motor down, I suspect its what ever component that is responsible for reversing polarity. Power is not locked out, it's just not correct, the polarity never reverses, it's the same no matter which button or combination of buttons I push. I guess what I need to see is a complete diagram of the system to really understand how it's supposed to work. The fact that I can jumper wire it to lift the drive, tells me that the solenoid and pump are fine, (they look new). I'll look for the trim shut off switch and trim sender tomorrow.

Re: 1971 Mercruiser 120 Questions

You have the newer 120........
I strongly recommend that you get yourself a Merc. manual # 1......
I would check all of the wires for condition/continuity.....
Look at the connections to see if they look ok.....
Here is one thing I might try.......
There is a switch that is actuated by the reverse lock out valve, (on the shift plate)....
It is red & brown & should have blues wires going to it......
I would try jumping that switch & see what happens......
The other possibility is the shut off switch......
Forget about looking for it from the outside, it is up above the bell housing & is unreachable with the bell housing in place.....
However, if you look on the inside of the transom, you will see where they enter the boat from the drive area.......
Since this switch is normally closed as well.....
I would try jumping that.....
According to the diagram, if you jump from the blue terminal on the up button to the terminal block with 2 blue on one post & one green on the other, it should have the same effect......
You need page 24 of section 3E of manual #1....
Maybe someone can post it up......
Anyway, hope this helps........