TOPIC: Need advice on mercury 80hp

I HAVE A 1971 MERCURY 80HP IT HASNT BEEN STARTED SINCE 1990 OR 91 IT SITS ON A 76 GLASSMASTER 16' THT WAS LAST USED AT THE SAME TIME IT HAS BEEN IN THE FAMILY FOR OVER 20YRS NEEDS FLR AND MAYBE TRANSOM??? N COMPLETE INTERIOR THE MOTOR IS LOCKED UP(I ASSUME)N 08 WHEN I BOUGHT IT FRM MU UNCLE FOR $800 I DID ATTEMPT TO TRY N GET IT RUNNING BUT DIDNT GET TO FAR DNT HAVE A KEY SO TOOK CONTROL BOX APART WAS GOING TO GET NEW IGNITION SWITCH BUT FOUND OUT THT MERCURY MAKES 12 DIFFERENT SWITCHES IS WHT I WAS TOLD BY LOCAL MARINE SHOP IN OKC,OK AT THT TIME ALSO FOUND OUT THT WIRING HARNESS IS BAD IF YOU TOUCH WIRES WITH YOUR FINGER THEY CRUMBLE HAVE BEEN QUOTED 1800 MINIMUM TO 5000 FOR A COMPLETE REBUILD PLUS LOWER UNIT N WIRING HARNESS N NEW CONTROLS I WANT TO KEEP IT N FIX IT BUT 5000 IS A LOT I COULD BUY A LAKE READY BOAT FOR THAT MUCH IS IT WORTH TO REBUILD THE MOTOR?ITS NOT THE $ TO ME THE BOAT HAS SENTIMENTAL VALUE TO ME ANY HELP OR ADVICE OR WEBSITES TO POINT N THE RIGHT DIRECTION WOULD BE GREAT THANK YOU

SHANE
P.S I KNW THT JOHNSON/EVINRUDE THE FLYWHEEL IS RIGHT ON TOP BUT ON MERCURY ITS UNDERNEATH A METAL HOUSING HOW DO U GET THT OFF TO ACCESS FLYWHEEL? IF I GET TO IT WILL TRY TO TURN FLYWHEEL IF IT TURNS THEN IT ISNT LOCKED UP

I suggest you were quoted those prices by a shop that was afraid of the job, and decided to scare you away

I wouldnt spend any money on keys, ignitions, harness's till you know if the motor is capable of even running...then you can purchase a good working set of controls on Ebay for $150

If you have some tools and a little mechanical skills we can help you diagnose your situation& get you on track, let us know...we can go from there with step by step instructions

Just a few nuts and bolts and that cover is out of the way !

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Or put a 15/16" socket on the flywheel nut and see if the motor is just stuck a little from sitting.

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Or maybe it locked up solid years ago while running and that is why it has been neglected all these years.

thank you for your help i hope tht it will turn was told to take spark plugs out and to put marvel mystery oil in the cyl n put plugs bk in and let it set n soak in is tht a gd idea i havent done tht yet im ase mechanic i love sbc 350 but dnt have a clue for outboards

I see / hear about this MARVEL MYSTERY OIL at times.Save your time and money !!

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Just put any oil in there for now.

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Even used 10W-30 will work for what you want to do.

First things first.... See if the motor will turn over. Like others have mentioned, get lots of oil into those cylinders and let it soak a few days.. After that see if you can move the flywheel either by hand or with a socket on the center nut. Go easy... A little movement in both directions. You don't want to break the rings. BTW make sure you're in netural
Below is my thread on a Merc 80 rebuild


forums.iboats.com/showthread.php?t=296896

Shane,
I don't think anyone answered one question: How to get at the flywheel.
After you remove the faceplate (spring loaded knob at the bottom needs a 1/4 turn to release the face) and the wrap (two releases on the front),...You will see a black release sticking down at the center of the front of the black top hat.
Trip that lever by pulling out on the bottom.
Then lift the top hat at the front to about 45 degrees. This will be enough to allow you to lift the top hat as you slightly move it aft.
Then the flywheel will be visible.
In the center might be a yellow rubbery plastic hole cover. Pry it out with a small screw driver and you will find the flywheel nut.
It requires a 15/16" socket.
The advantage gained in use of Marvel Mystery Oil over common oil is that its molectular structure is smaller and consequently penetrates deeper and faster than common oil.
I'm not real sure what it is made of - perhaps ATF & kerosene???, but it is worth every penny.
Caution in taking the time to carefully allow lube to get down the sides of the pistons before attempting to turn the flywheel after such a long lay-up will help avoid unneccesary scoring that can be caused by dry rings moving across dry cylinder walls or cylinder walls with a patina of rust from years of ambient moisture being allowed to collect in the beast.
IF you find that the flywheel won't turn (and other than gentle rocking back-n-forth only turn it clockwise to avoid damage to the water pump's impeller),...It is time to remove the lower unit (gear case) so you can determine if the pistons are seized or if the lower unit is seized (more common in neglected outboards that a dry seized powerhead).
I have attached a picture with instructions to remove the lower unit.
Granted,...Concern for the old water pump impeller at this time is not neccesary as you will definitely want to install a new impeller before you're finished, but it is good practice to NEVER turn a flywheel counter-clockwise so that when it does matter you will already have yourself trained.
It is possible that the old ignition switch still has a three digit number on a white sticker attached to it. That is the Mercury key number required.
The wiring is commonly thrashed. In some cases they can be cut back to somewhat decent wire and re-soldered to the ignition switch for function as you determine whether or not you have reason to later spend good money on new wiring, etc.
Once you get the powerhead to turn smoothly - check in so we can explain the critical steps required to check compressions, test for spark, etc, etc, without damaging valuable components that are getting scarcer and scarcer.
Thom