Topic: 1957 Evinrude Lighttwin 3 compression – Antique Outboard Motor Club,Inc

This topic has 11 replies, 7 voices, and was last updated 7 years, 7 months ago by fleetwin.

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June 4, 2017 at 7:05 pm #7231
outbdnut2
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Working on a 1957 3HP Evinrude that hasn’t been run in 30 years. I had it briefly fire for a couple seconds a couple of times. I put some oil in the cylinders to seal up rings and it fired again briefly. A compression check confirmed my suspicion giving 30 pounds in both cylinders. I then checked compression on a similar year 3 Johnson that runs good for a sanity check on the compression gauge and that one was 60 to 65 pounds, so the gauge is working OK.

My question is: Is this likely stuck rings? or is there something else this model is known for that knocks compression down? What are the odds I can free up rings by tilting the motor up and putting some solvent like liquid wrench or transmission fluid in the cylinders for a soak? or should I just start tearing into the crankcase?

Thx,
Dave
June 5, 2017 at 12:00 am #58991
frankr
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Head gasket may be blown between the cylinders.
June 5, 2017 at 12:24 am #58992
david-bartlett
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I agree with Frank. Both cylinders that low could very well be a head gasket.
June 5, 2017 at 1:34 am #59000
Tubs
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Put me down as #-3 for a head gasket.
Equal compression in both cylinders is a pretty good indicator.
If it were rings you would expect some variation.

A "Boat House Repair" is one that done without having tools or the skills to do it properly.
June 5, 2017 at 1:45 am #59001
Mumbles
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Being a bit of a rebel, I’ll go against the grain and say it could be scored pistons or cylinders causing the low compression. If the head gasket isn’t blown, removing the exhaust cover might show some piston damage.

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June 5, 2017 at 1:15 pm #59020
david-bartlett
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"Some piston damage"? Glad it wasn’t "Serious damage"!
June 5, 2017 at 2:25 pm #59032
outbdnut2
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Thank for the tips – I’ll pull the head next. Somewhere in it’s life, the head was replaced with a green Johnson head.
If there is major damage, I have two parts motors that can donate. Hopefully all I need is a new head gasket.

This motor has sentimental value to the owner because it was her Dad’s.
Dave
June 5, 2017 at 2:37 pm #59035
Mumbles
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Hopefully it is just the gasket and nothing else. The heads tend to get a concave shape over time allowing the gasket to blow in the middle so it’s highly recommended to straighten the heads surface out while it is off. This can be done with wet ‘n dry paper and a piece of plate glass.
June 5, 2017 at 4:59 pm #59053
garry-in-michigan
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I use 440 grit ‘Wet or Dry’ . . . 😀
June 5, 2017 at 10:20 pm #59073
outbdnut2
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I pulled the head and the gasket was blown, looking like the photo Tubs posted.
Thanks for the heads up on the head gasket!
Dave
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