1988 Johnson 70hp inspection

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cesandroid

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Howdy everone. Got a 1988 70hp that seemed to be running good other than possible 2 cylinders on idle but more specifically at top end was getting 38mph but now 32 with gps rpm 5400 rebuit 13.25x17 prop. havent gone into depth yet but thought i would the take head off and see. Firstly compression 1-127 2-117 3-117 cold, throttle closed. hmm i can see in the pictures why 1 is higher i believe. Bottom 2 bit of scoring on exhaust but no finger nail catching. unburned fuel on pistons and rebuilt whenever that was with 2 over on the pistons. new to me. Just getting thoughts on the pictures. plugs looked dark and kinda wet as well. Thanks
 

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racerone

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Motor has to come apart.----Does hose for the tell tale come off the side of the block or the top?
 
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Crosbyman

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from chat gpt.. some don't like SEAFOAM some love it...Merc engine tuner seems good to


1757163519524.png
 
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cyclops222

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Time for a resurfacing of the block & cylinder head. Possible careful small SS wire wheel to clean piston heads. Very doable.
 
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racerone

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There are score marks on the cylinder walls.----Pistons are likely scored as well.----This motor can / will run.-----But it should be taken apart for proper repairs.----Little bit of carbon on pistons is normal and causes no harm.
 
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cesandroid

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Appreciate the feedback. It does run alright but could be better. I think Ill take on racerone's idea and open it up. Is there a recommended piston for this motor?
 
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racerone

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Post pictures of pistons after you open it up.----Need to try and determine what happened.
 
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cesandroid

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So talked to a machine shop today and said they prefer not to fix 2 cylinders but do all 3? if 2 are say next size up compared to the good cylinder..thats not good? Just getting another opinion.
 
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tphoyt

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If it were me that’s what I would do. Just start fresh. As mentioned before post some pics to see if we can help determine why this happened so it doesn’t happen again.
 
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saltchuckmatt

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cesandroid said:
So talked to a machine shop today and said they prefer not to fix 2 cylinders but do all 3? if 2 are say next size up compared to the good cylinder..thats not good? Just getting another opinion.
Click to expand...
I'm with Tim on this otherwise I would just hone bore the two and take my chances.
 
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Crosbyman

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37 years, it had a good life...run it till it dies peacefully or with a bang.
Just bring a kicker and a phone. The aging population ... like me ....are close to dumping gazillions of OBs on the used market....even good ones !
 
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racerone

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These are excellent motors..-----Rebuild it with 3 new pistons in there.-----But you must determine the cause of the damage.----Run it for another 20 years.
 
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saltchuckmatt

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I hate to disagree with race but finding a good used new to you outboard is a better financial decision.

I live in Seattle and we don't have a marine machine shop anymore.
 
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racerone

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Good used outboards with warranty are few and far between.-----Many 2 strokes are ruined by folks who do not know how they work.-----Folks invent new ways to destroy them on a regular basis.-----Learn to rebuild it properly and you will have affordable boating for a long time.
 
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cesandroid

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Got the motor on the bench. Going to start with the teardown. I will post pics of what everything looks like. Thanks for the info guys! JFI machine shop up here quoted 225 for bore and hone per cylinder. Pistons they figure WSM from the US.
 
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racerone

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Well----Perhaps the only shop in your area.----But with the right tools about $100 / cylinder does the trick.
 
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