1987 Merc 70 HP (3 Cyl)

[TD_Maker]

Hello to everyone. Football is taking up some time right now; however, I have managed to get into this new-to-me motor project in my spare time. Compresssion test: Top: 115 Middle: 115 Bottom: 108 What do you guys think? Am I good to go forward?

I have an issue. I am replacing the impeller, and I noticed oil leaking from the shift rod shaft in the lower unit. In fact, quite a bit of oil leaks out especially when the motor is tilted. I want to go ahead and reseal the entire lower unit as long as it is off. Here is the question. I have limited experience with Merc Lower units other than impellers etc. Should I have a mechanic reseal the unit, or is it something I can tackle myself? I am generally a do-it-yourself type of dude, but I am lacking a litle confidence when it comes to pulling gear shafts etc.

Appreciate any help.

 

[oldman570]

Re: 1987 Merc 70 HP (3 Cyl)

The compression should be OK. The seals in the LU can be replaced with a good manual and the correct tools. A pressure test of the LU should be done to check all the seals before hand and to check the LU case for leaks. With time, tools, and patince you should be able to fix it. First thing to do is get a OME service manual and do some reading as how and what it takes to do the work. Then you can make a better choise as to if you want to tackle the job. JMO
Oldman570

 

[Maxz695]

Re: 1987 Merc 70 HP (3 Cyl)

View attachment 173672View attachment 173673View attachment 173674 The seals at the top of the shift shaft in the lower unit looks somewhat like this. If you can get the top screw loose the seals there can be replaced. Do not let the shift shaft come up or the cam there at the bottom of the shaft pictured above will slide off the shaft and the unit will have to be dismanteled to get it back on unless you get real lucky to get it lined up again without it moving. Did you test the compression dry without spraying some premix into the cylinders? This will give you a more acurate reading after working the oil in by turning the flywheel aroung a few times to lube the rings. Remove the plug wires and test one cylinder leaving the plugs in the other cylinders until there turn Item 37 through 41 http://www.marineengine.com/parts/m...ng-assembly-complete-serial-group-no-3-page-1

 

[CharlieB]

Re: 1987 Merc 70 HP (3 Cyl)

Is it gear oil or unburnt residue from the exhaust?

Get a dab on your finger and smell it, gear oils have a distinct odor totally different from the smelly burntness of exhaust residues.

If they gearcase oil level stays up and is not getting water into it, your mess may just be exhaust related.

 

[TD_Maker]

Re: 1987 Merc 70 HP (3 Cyl)

Charlie,
Without a doubt, it is gear oil. i am beating around if I want to tackle this job or if I want to just take the Lower unit down to the local guy and let him do it. The more I read about it, the better I feel about it.

I am having an issue with removing the Lower unit though. I absolutely have all the bolts removed, but the darn thing seems to be hung up somewhere. Does the shift rod linkage have to be disconnected (like an old OMC V-4) and where is it disconnected at in this older Merc? Not much room under the carbs.

 

[CharlieB]

Re: 1987 Merc 70 HP (3 Cyl)

The shift shaft is a spline that slips into a splined coupler.

The hang up is often the spline on the vertical shaft hanging in the internal spline of the crankshaft.

Many owners fail to smear the splines with spline grease whenever the lower is off for water pump service, sometimes the splines wear or corrode and hang up.

Sometimes you can get lucky, ground the ignition so the motor will NOT start, crank the motor while holding a just bit of downward pressure on the lower. Just don't start the motor. Hopefully the lower will simply fall loose.

Then again, I've seen some that have had to be stood on their head (upside down) and soaked in PB Blaster or Kroil for a week before they came loose.