1988 Johnson 70HP

mkaminski

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After over a year of looking, I have finally found a no-compromise motor that looks like it would suit my needs perfectly. It's relatively new, an OMC, new electric trim & tilt motor, and 3cyls. I figure that a 3cyl is a bit better on fuel economy. <br /><br /> http://newyork.craigslist.org/wch/boa/127252444.html <br /><br />The seller replied that he would sell for $800. I shot him an email asking what kind of service has been done on it and when the water impeller was last changed. I feel like I would be inconveniencing him if I asked for a startup demonstration on the water muffs, but it would be important to see that it starts up, right? <br /><br />In an earlier post he wrote, "this is the loop charged inline 3 the more desirable 70, more torque than older 70's." What does that mean?<br /><br />Is there any new hardware that I'll have to buy in order to replace my Evinrude 35? (The boat's max HP rating is 85) I have Johnson Shipmaster controls installed, OMC starter, and a teflex steering system.<br /><br />Any input on the latter or the motor would be appreciated!
 

JB

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45,907
Re: 1988 Johnson 70HP

I wonder what "older 70s" he refers to. After about 1985 they are rated at the prop and before that at the crank, but I am not aware of any torque increasing mods. They just retuned it.<br /><br />That engine started out as a 55 in the late 60s, and has been rated as high as 75hp in higher states of tune.<br /><br />It is a good, economical and reliable engine for a carbed 2 stroke. I have had three and they all were excellent engines.<br /><br />I suspect that your controls can be used, but you better get that advice from someone who knows more about it than me.
 

rickdb1boat

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Jan 23, 2002
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11,195
Re: 1988 Johnson 70HP

mkaminski<br /><br />Most definitely, you want to run it. A compression test would put your mind at ease, too. At least you would know the basic condition of the motor inside. Buy or Borrow a tester(Good to have anyway) and take it with you. Only takes a couple of minutes to check it.. It would also be nice to check out the lower unit fluid, if possible..<br /><br />BTW- Ihave a 1991 70 HP Rude and it has been a great motor from day one...
 

mkaminski

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Re: 1988 Johnson 70HP

I just went upstate and bought the motor today for $800. The compression numbers are 110, 110, 105. He demonstrated the motor, and it cold started well.<br /><br />I took it home today, and it's the same shaft length as my old Evinrude (20"), but the mounting bracket is much longer than the Evinrude's. I am afraid that the lower half of the bracket may actually extend below the water line. Could that be damaging to the trim motor? From my measurements the motor AV plate should level out with the bottom of the transom on the fourth bolt hole.<br /><br />Also, I'd like a little more piece of mind with my transom. Do you know where I can get an aluminum reinforcement plate like the one below?<br /><br />
 

Dhadley

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Feb 4, 2001
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16,978
Re: 1988 Johnson 70HP

The trim motor is going to get wet no matter if its below the water line or not.<br /><br />And on the looper deal -- there never was a 3 cylinder Evin / John that wasn't a looper. In 1986 they introduced a 56 cid 3 cylinder. The older 70's were 49 cid. Obviously the 56's will have a bit more torque.<br /><br />Post the model number and we'll figure out what year it is.
 

mkaminski

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Re: 1988 Johnson 70HP

I just mounted the motor today with 3 other guys. I have the motor clamped to the transom for now until I get the right drill bit.<br /><br /> <br /> <br /><br />The antiventilation plate seems to be level with the bottom. Is it all right that the bottom bolts will be installed below the water line?<br /><br />Dhadley, I'll get that model number.
 

Dhadley

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Re: 1988 Johnson 70HP

Most all bottom bolts are underwater. Thats why its important to seal them. DO NOT USE 5200! Youll have a heck of a time getting the motor off to raise it later.
 

rodbolt

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Sep 1, 2003
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Re: 1988 Johnson 70HP

unlike Dhadly I use 5200 on any underwater fittings, however thats just the way I do it. a good subsitute is boat life caulk. DO NOT use silicone as it will leak and allow water intrusion into the transom wood creating a rot issue.<br /> eventhough some manuals reccomend silicone its been past experience it does not seal well.<br /> the only real issue I ever had with the 3cyl motors that used the lost foam casting block and head assy's is in salt water the head gasket gets deformed with corrosion occasionally.<br /> mostly it was a very reliable engine if set up correctly.<br /> but like Dhadly says if you use 5200 it may take the gelcoat off when you move the engine again.<br /> I once lifted a 28ft mako with twin 200 yamahas off the work rack by the bond between the bracket and the transom that had been sealed with 5200. had a whale of a time removing those engines.
 

andy6374

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Aug 4, 2005
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Re: 1988 Johnson 70HP

3M 101 sealant works well, it's rated for below the waterline and doesn't have the physical properties like 5200. 3M 101 is very similar to boat life caulk.
 

mkaminski

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Re: 1988 Johnson 70HP

I bought some black adhesive from Boat US rated for below the waterline. After drilling in the transom I found that the wood is somewhat moist. :( <br /><br />Anyhow, the engine is mounted on the transom and its very solid. I used the entire tube of adhesive in every nook and cranny. Next I have to connect the throttle/shift cables, wiring harness, and the choke.
 

PierBridge

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Re: 1988 Johnson 70HP

By the way that was a steal for the Motor.<br /><br />Good Job.
 

Texasmark

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Re: 1988 Johnson 70HP

Only other thing I would suggest is to change the thermostat. My rude 70 burnt up due to my ignorance about the thermostat (even having one) and it sticking closed. Engine was several years old when I bought it and didn't know to keep outboard's thermostats "fresh"...like on here folks recommend replacement every 2 years. Great advice and a "stat" now and then is sure cheaper than a $1000 overhaul. You can change it yourself....just don't overtorque the bolts holding the cover on and be careful removing them so that they don't break off. Remember you are screwing into aluminum.<br /><br />Otherwise my '75 70 was a super performer.<br /><br />Mark
 

mkaminski

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Re: 1988 Johnson 70HP

Thanks mark...I'll keep that in mind. I have to get a manual - I'm not sure how useful my Clymer's manual for 2-40HP motors will be.
 

mkaminski

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Apr 20, 2005
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Re: 1988 Johnson 70HP

I tried hooking up the controls today. It seems that the output fitting are incompatible. I had a 1982 Evinrude outboard that had the controls connect externally. The output fitting on these cables seem to be long. I can't seem to find the right one on iBoats...any suggestions?
 

surlyjoe

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Nov 21, 2005
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Re: 1988 Johnson 70HP

the transom may seem solid, but that fact that the wood is damp is definitly a sign to keep an eye on it for any stress cracks or sagging...
 

mmainelli

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Jan 4, 2006
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Re: 1988 Johnson 70HP

There's no reason your lower engine mount bolts should be in the water. How deep is the notch cut in your transom? Remember, the cavitation plate should be even with the keel line. That position will determine the placement of the mounting bracket on the transom, and the bolt holes. And if the bracket still touches water, use higher bracket bolt holes. The lower bolts suffer little load, other than supporting engine weight. The major load is on the upper bolts, when the engine is underway, and the prop puts a coupler torque load on them.
 

mmainelli

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Re: 1988 Johnson 70HP

Another point. I have a re-built Johnson 1983 75 hp hanging off the transom of my 17' skiff. I traded up from a J40. The 75 is about 80 lbs heavier and I had to change my waterline. But my bracket is still not in the water, because I mounted according to cavitation plate/keel alignment. But I've forsaken T/T sender/gauge, temp gauge and rpm gauge. I T/T looking foward, according to my load, bow position and engine whine. For temp, I check the pisser occasionally. For rpm, I keep it high with a proper boat trim. Forget all the dashboard stuff. You'll just get into an accident or be knocked off by a wave. Get to know your boat and motor.
 

mkaminski

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Apr 20, 2005
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Re: 1988 Johnson 70HP

The antiventilation plate is lined up with the bottom of the transom.
 
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