70 hp Johnson gearbox

Discussion in 'Outboards' started by squalus, Mar 10, 2013.

  1. squalus
    Joined: Mar 2013
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    Location: cape town

    squalus Junior Member

    Hi there,i just bought a 21 ft robcraft with two 1978 seahorse 70 hp Johnson outboard motors(i think its 1978,they also look old).the boat needs some care, prepared to do it...been standing for 3-4 years,so want to do a service,got carbs off and new spark plugs....BUT REALLY battling getting the sternleg off,all bolts are loose even the gear selector one under the carb,want to check the water pump.any help out there,really want to get the ball rolling on this project
     
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  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Is the shaft stuck in the crankshaft? There is a spline that sometimes gets rusted and is very hard to take off. If everything else is loose, that is the only part that can be still holding.
     
  3. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Hummmmm, stuck output shaft on a 35 year old outboard. Go figure.

    The first thing to do is grab the lower unit and shake the living hell out of it. If this doesn't work, a dead blow might talk some persuasion into it (it usually doesn't). If you can get it to move a little, some penetrating oil, liberally applied might help. Doers the leg twist, but not drop?
     
  4. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    The internal splines on the crankshaft rust, and although the driveshaft is some kind of stainless, they get seized together. Not sure how PAR can get the penetrating oil in there, it is inaccessible to my knowledge. If you do get it apart, be sure to put plenty of grease and a new ring seal on that drive shaft spline before re-installing.
     
  5. squalus
    Joined: Mar 2013
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    Location: cape town

    squalus Junior Member

    Thanks all,will try them all and will keep in touch with the progress,would you guys think it would be better to try and sell the engines for more modern ones? They say these Johnson motors are pretty hardcore,heavy on juice but reliable....
     
  6. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    One thing they were not, is heavy on the gas. But at that age things could be pretty tired !
     
  7. keysdisease
    Joined: Mar 2006
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    keysdisease Senior Member

    Have you disconnected the shift linkage? Maybe in that vintage an oval port with 2 screws about 1/4 way down the leg, open it and access the link connector. Not sure if they still did it that way in "78

    Steve
     
  8. squalus
    Joined: Mar 2013
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    Location: cape town

    squalus Junior Member

    Hi Steve,these motors don't have those screws,but saw it on a older 25 hp Johnsons...STILL BATTLING thou...so this is what i think i should do,going to start the motors without checking the water pump,cause i don't know if the motors start or not and just maybe it will shake things loose and then check if the water pump works by checking if its spraying water.but i know i need to check the pump...
     
  9. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    Yes, run the engine initially, checking the tell-tale to see if water is getting up into the powerhead. Do a compression check (follow instructions in manual to avoid damaging electrics) to see if it is up to specs. If it really is rusted-in badly, there may be a problem of not having enough good spline left after you separate them. IF you can separate them ! I have had this problem with a V4 Johnson years ago and it is a trying exercise. From memory I had to cut the shaft, which wasn't that big a deal as I had plenty of spares, but that way is no use to you.
     
  10. squalus
    Joined: Mar 2013
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    Location: cape town

    squalus Junior Member

    Cool,thanx...going to just that while seeing if i can get other motors.got the word yesterday the sailor who's boat it was,was quite the fisherman and the motors got some hours on them,so i think its like you said there might not be enough spline left to sail...but will keep posted...
     
  11. boatbuilder41
    Joined: Feb 2013
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    Location: panama city florida

    boatbuilder41 Senior Member

    Did you get lower unit removed yet??? Under the zinc steering torque tab is a hidden bolt. Remove torgue tab located just above propshaft splines. I wouldnt worry to mulh abut the driveshaft splines if. I if you have any more problems i will be happy to help out. The three cylinder omc is a very impressive engine i removed a 200hp evinrude vindicator from my boston whaler and replaced with 2 65hp stingers. Its faster.cheaper to run. And more dependable. You will be very impressed
     
  12. squalus
    Joined: Mar 2013
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    Location: cape town

    squalus Junior Member

    No its still on but the one cool thing is i managed to get a hole service manual(on CD,gonna turn it into a book form).i did try and see if there was a bolt there bur couldn't get the tab of,just need a bigger power bar (pretty tight)and see what's under there.shot thanks will definatly call on you if i get stuck,will definatly get stuck sooner or later...but yeah wanna have faith in these motors...
     
  13. boatbuilder41
    Joined: Feb 2013
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    Location: panama city florida

    boatbuilder41 Senior Member

    I run these 3 cylinders many years for commercial use. I would not have any otherkind. Any way i can help out, just let me know......
     
  14. squalus
    Joined: Mar 2013
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    Location: cape town

    squalus Junior Member

    Shot boatbuilder41,you called it..got my t bar took the torque tab off and there it was...thanks man,its off now,gona check,clean and grease...thanks to all!!!!
     

  15. boatbuilder41
    Joined: Feb 2013
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    Location: panama city florida

    boatbuilder41 Senior Member

    Great!!!!!! . If you need any parts just let me know. I have a shop full of 3 cylinders
     
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