What is the trick for getting lower unit off 1978 80hp Mariner

jhoelting · #1 June 2nd, 2009, 03:10 PM

Does anyone know if there is any special procedure in removing the lower unit on a 1978 80 hp mariner. I've got the bolts loose but it doesn't seem to want to slide down. Retainer clip? Big Hammer? Lots of kicking?

Chris1956 · #2 June 2nd, 2009, 03:38 PM

There is a bolt hidden under the zinc anode. After you have that one out, you need to spray some penetrating oil on the studs and wiggle it off. Gentle tapping on the front stud (nut on flush) also helps to break it loose. You can gently pry down on the midsection studs as well.

jhoelting · #3 June 3rd, 2009, 12:41 AM

don't get me wrong, or pass judgment too quickly as to my ability, as I can do alot of tasks as Iam pretty savy when it comes to alot of things such as motors and other fixes, but what is a zink anode. Believe me, if i can get this motor running on my own,(with your help), after spending all the money I have with "professional" mechanics, I'll buy the shop manual.
But Im on my last leg with the motor and am hoping the exhaust ports are plugged. That is why I am taking the lower unit off, in hopes of the exhaust ports are plugged, my hope is to unplug them and it will solve a problem. otherwise the repairs on this motor has cost me $$$ in repairs that went nowhere and years of fishing and fun.
Otherwise I will scrap the motor and will try my luck with another. I should have quit on this motor long ago but it just didn't happen so.....

jimg984 · #4 June 3rd, 2009, 08:45 AM

its the trim tab

jhoelting · #5 June 3rd, 2009, 09:21 AM

Ahh, thank you both. I dreampt about it alittle last night a thought that might be one in the same. You ever hear of exhaust ports on an outboard getting clogged? It is kind of my last resort to this motor having replaced most of the electrical system(harness, trigger, stator, power pack) the ignition system seems to be working. Carbs have been rebuilt and gone through several times. New fuel with Seafoam, fuel lines, fuel filter has been clean, we installed a Merc fuel/water separator. Compression has been checked all 4 cylinders have around 137+/- psi.
Anyhow it chugges and then dies underload. I can coaxed it into running highspeed but it dies at slow speed. So no-waking and docking is impossible.

Chris1956 · #6 June 3rd, 2009, 10:34 AM

I hope your exhaust ports are clogged, however, that would be surprizing. what are the symptoms? Lack of quality idle?

Have you had the motor linked and synched?

mmccoy555 · #7 June 3rd, 2009, 10:58 AM

Make sure you disconnect the shift shaft. It's either connected half way up the shaft or up underneath the motor in the back.

Chris1956 · #8 June 3rd, 2009, 11:33 AM

The shift shaft is coupled just above the gearcase. The shafts simply pull apart.

mmccoy555 · #9 June 3rd, 2009, 11:37 AM

Quote:

Originally Posted by Chris1956

The shift shaft is coupled just above the gearcase. The shafts simply pull apart.

yes but there should be a pin in there to hold it in. Again I'm not familiar with that particular motor but that's usually the case.

matinicus · #10 June 3rd, 2009, 01:19 PM

Quote:

Originally Posted by mmccoy555

yes but there should be a pin in there to hold it in. Again I'm not familiar with that particular motor but that's usually the case.

The big Mercury/Mariner motors have a spline connector for the shift shaft without any retainer.

Depending on the configuration of the studs and nuts, I have sometimes placed a spacer just above each upper studs with nuts, and the small cavitation plate above. For example holding the flat surface of a 1" open end in that gap. Then backing off the nuts slightly, this will put some load on separating the lower unit-- maybe enough to get a little space in there.

Use a good pentrating lube (blaster? Gunk?) and time and patience- on all of the studs. Eventually you can tap the back of the gearcase just above the trim tab on either side with a wood block and dead blow hammer and get some movement. When lower unit is off, replace impeller, pump plate and pump insert cup before reassembly.

At reassembly polish all studs and coat with Merc/quicksilver anti-corrosion grease or a "neversieze" that is compatible with aluminum and steel.

Also at reassembly do NOT put any grease on the top of the drive shaft spline. Only on the sides. The top must maintain an air space else you will put a loading on the crank beargins-- a bad thing.

Don't know what is wrong with your motor. It is possible to plug up exhaust where you are looking if some animals made their home in there. Otherwise this is unlikely. I suggest taking the time to check compression in all cylinders and also that stator is fully active in low rpm mode and high rpm mode. It is possible to have an engine that fades out over 3000 rpm because the hot-high rpm ignition is out of commission due to stator failure. Also it is possible to have stuck rings, scored cylinder, burned piston, cracked reed--- any or all which would show up in compression checks to point you in direction.

If you suspect "carbon" blocking ports, the most likely place is right at the exhaust ports--- remove the cover on the side of the powerhead to access this area. If it is plugged up, this is almost always due to inferior lubricants. I had a 1964 85 hp six, run about 100 hours a year, every year (on salt water-- and moored all summer) 'till I replaced it in 2005 (with a 1976 I6 model) just to get "power trim" with the integral transom bracket, and electronic ignition. It always used quicksilver or mercury oil and did not get carbonned up at all. Even when I replaced the shift shaft around 1999, and lifting the powerhead could see down into the housing, and up into the exhaust chamber there was only a black sooty surface, no gummy tar like residues. Thats an engine that was run for more than 40 years without disasembly.

jhoelting · #11 June 14th, 2009, 05:13 PM

Thank you all for your post on this subject. I have had the lower unit off and back on again. Like Matinicus stated, the likelyhood of this being clogged unless by and animal or vermin was slim. Although there was a little carbon build up and it was stickey, and not very much at all, and in no way that I could see would hinder the performance of this motor. My next project is to try to get to the exhaust ports up in the power head.
This motor was worked on by a mechanic at one time. But after replacing stator, trigger and a powerpack or two and wiring harness rebuilding carbs. The boat still doesn't like to run under pressure. I hope to find clogged exhaust ports, as I am pretty unwilling to spend much more money on this outboard.
Does anyone have any suggestions as to getting to the Exhaust ports at the power head?

Chris1956 · #12 June 15th, 2009, 10:58 AM

You need to pull the powerhead and maybe the exhaust cover. I really think you are barking up the wrong tree, however. Those ports are pretty large, and I think very likely to be clogged.

Usually when an inline merc dies whn trying to accelerate, it is lean idle mixture. You might try opening the mixture screws 1/8 turn and trying to accelerate. Alternate the acceleration and the adjustment on each carb. I think that may just fix it.

BTW - If your exhaust ports are clogged, why would it run at high speed?