1978 115 Johnson Compression

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Dec 23, 2014
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I am considering buying a 1978 115 Johnson with 120ish compression on 3 cylinders and 70 on the 4th. Is this motor worth buying?
 

boobie

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Nov 5, 2009
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No. If it's not a blown head gasket, I'd stay away from it. JMHO.
 

boobie

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No. If it's not a blown head gasket, I'd stay away from it. JMHO.
 

Faztbullet

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Mar 2, 2008
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Is 70 PSI really that bad? I've seen people on here say that 70 isn't too bad for an older motor.
That a 50 psi difference between cylinders and that's bad news......
What could be wrong with it?
Blown head gasket, rolled ring damaging cylinder, detonation damage, etc,etc.....
 

emdsapmgr

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Dec 9, 2005
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New from the factory compression would have been in the 125 range on all 4 holes. The guys have given you good information. The value of that engine is what the individual parts are worth-as a non-running engine. Trim system, lower unit, etc. If the ring let go, the head could damaged on that side.
 

racerone

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Dec 28, 2013
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If you get it for say $200 or less and can repair it yourself it can be a good deal..----Obviously there is someting wrong in one cylinder.---Broken rings was / is very common on them.
 

bob johnson

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Feb 25, 2009
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the lesson to be learned here...is that it is NOT JUST a #'s difference... it is a story of the motors condition...something is WRONG with that cylinder.. could be a head gasket( cheap)...or it is broken rings, damaged cylinder walls, or both....and those issues wont go away...fact is they might get worse... a guy might buy that motor for a parts motor if he has a similar model..
 

rothfm

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Sep 26, 2006
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"Worth-it" is a very conditional phrase depending on who speaks it. Some folks on here would do their magic and rework it, because they really like to do it. Others couldn't be bothered, don't have the experience, patience, money or a multitude of other reasons...All valid reasons.

Depends on where you fall in those groups, and what your looking for. it could be.... But 70psi is bad, dont even try it.

Example: I got an old 1984 115 with a bad cylinder 200bucks...Took me a year to finally get into it. When I did, all I needed was one piston, all rings, seals etc.... and I put it back together...It kept me fishing all Season when my primary broke. Still a great runner for "Short Money". But I had the time, and desire to do it myself.

Now, if you had to pay to have the rework done...Probably not worth it, unless you have an orchard of dollar trees in you backyard and money is not object. If that was the case you'd be opting for something new I guess.
 
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