trying to evaluate my 1960 Johnson 75hp.

About inboard or outboard motors.

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Retroman
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Joined: Mon Apr 25, 2011 5:08 am
Location: Great South Bay, Long Island, NY. Building a Zip/Flying Saucer

trying to evaluate my 1960 Johnson 75hp.

Post by Retroman »

Would you mind taking a look? Any advice is greatly appreciated.

http://www.youtube.com/watch?v=AZUJKqKMoUw
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RetroMan
Built A Zip/Flying Saucer. I do my boating on South Oyster Bay, Long Island, NY
Documenting my build on YouTube @ http://www.youtube.com/SuperUnknownMC

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vupilot
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Re: trying to evaluate my 1960 Johnson 75hp.

Post by vupilot »

You say youre still getting good compression on your compression guage? Checking warm will usually error on the high side, a cold check sometimes will be lower. Thats a pretty good amount of piston damage, I've seen similar damage from an engine that was revved really high straight after a cold start or it could have been operated normally but overly lean to cause damage like that. Hard to see the damage of the cylinder in the video but from the pictures the part I can see doesnt look all that bad.

Moeregaard
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Re: trying to evaluate my 1960 Johnson 75hp.

Post by Moeregaard »

I see some carbon buildup, but the bore looks pretty good.

-Mark Shipley
A boat is just a wooden box with no right angles.

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Roberta
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Re: trying to evaluate my 1960 Johnson 75hp.

Post by Roberta »

The most important thing is the seal between the rings and the cylinder walls. Scuffing on the pistons could be caused by them rocking from predetonation from the carbon buildup and/or running lean due to the carb being loose or possibly carbon deposits breaking off and getting between the cylinders and pistons. How does the compression you got compare to what the MFG says you should have and how does it compare to the other cylinders? should be within 10-15% of each other. For sure, clean up the carbon on the upper cylinder walls and the top of the pistons.

Roberta
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

Retroman
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Location: Great South Bay, Long Island, NY. Building a Zip/Flying Saucer

Re: trying to evaluate my 1960 Johnson 75hp.

Post by Retroman »

Thanks Guys,
The compression is within 5lbs of each other, at about 80 pounds per, done on a cold motor. Im gonna put it back together, run it and hope I get a season out of it. I wont invest much money, as the motor is damaged.
Thanks again
Jim
RetroMan
Built A Zip/Flying Saucer. I do my boating on South Oyster Bay, Long Island, NY
Documenting my build on YouTube @ http://www.youtube.com/SuperUnknownMC

Retroman
Posts: 199
Joined: Mon Apr 25, 2011 5:08 am
Location: Great South Bay, Long Island, NY. Building a Zip/Flying Saucer

Re: trying to evaluate my 1960 Johnson 75hp.

Post by Retroman »

Another silly OMC question. It seems odd, only one cylinder was damaged. The carb may have been loose, as the bolts are stripped, and it was pointed out to me this could have caused a lean condition in the one and only damaged cylinder. I was curious if the loose and frozen bolt in the pic, could have let exhaust gases seep into the cooling system and affected only the top cylinder in this photo??
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RetroMan
Built A Zip/Flying Saucer. I do my boating on South Oyster Bay, Long Island, NY
Documenting my build on YouTube @ http://www.youtube.com/SuperUnknownMC

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Caber-Feidh
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Re: trying to evaluate my 1960 Johnson 75hp.

Post by Caber-Feidh »

Not that bad It does not look like a typical lean run. Don't worry about predetonation, you couldn't make those old low-compression engines knock on nitroglycerine.

Scuffing like that is typical foreign object/material. I have seen excessively carbonized engines scuff very much like that. The scuffing looks like it runs all the way above the top of the upper ring apex. It is likely from chunks of carbon trapped between the piston and the cyl.The polising around the ports shows the bore is out of round, the area around the ports is a weak spot, and will deform with age, use, abuse. It's not significantly bad, just an observation. If you really wanted, you could drop a hone down it, and re-ring that piston, but IMNHO it's not that far gone.

The old dino-oils were not even close to a modern synthetic, about every non-chorme/nikasil jug you see on a 50 year old 2-smoker will look like that from oil coking. Don't worry about it. Knock off the loose carbon, don't let it get into the case. go 5 points richer on the mix to deal with some possible roughness, and use a decent synthetic instead of that bug-fogger fluid from the last century, and if you have fixed any possible vacuum leaks that old wheezer will go another 10 years... maybe at 50HP, but it will keep going.
Some plan to stroll through Saint Peter's Gates, I plan to go through them at 150mph... backwards... in a screaming ball of flame, with a glimmer belt wrapped around my head, and a NOx button in my hand.

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