70 hp Johnson gearbox

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

 

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.

 

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?

 

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.

 

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....

 

One thing they were not, is heavy on the gas. But at that age things could be pretty tired !

 

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

 

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...

 

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.

 

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...

 

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

 

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...

 

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......

 

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!!!!

 

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