Topic: 18 Evinrude compression. – Antique Outboard Motor Club,Inc

This topic has 12 replies, 8 voices, and was last updated 9 months, 3 weeks ago by labrador-guy.

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February 7, 2024 at 6:02 pm #284735
elgin2
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I have a ‘60 Evinrude 18. What is decent compression numbers. I’m getting 75 on top and 60 on bottom. Motor hasn’t run in 2 years I was told. Thanks in advance.
February 7, 2024 at 6:23 pm #284736
elgin2
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US Member
Just found it has a oily mag. Maybe effecting the compression numbers.
February 7, 2024 at 7:27 pm #284737
frankr
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US Member
Oily mag is not causing the low compression but could he result of a common problem like a worn out powerhead
February 7, 2024 at 7:29 pm #284738
Steve Martin
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An oily mag indicates an upper crank seal problem but that will not effect compression numbers. Your numbers are low and the spread (60/75) is much too wide. If you can get it running and then retest compression it may increase somewhat.
February 7, 2024 at 7:42 pm #284739
labrador-guy
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If the PO says it hasn’t run in two years they probable really mean four years. Chance’s are the rings are sticky. Compression numbers on motors that have been stored a long time really don’t mean diddly! JMHO Expect the worse maybe if it will run even poorly it will come back to life for you. I have four 18’s all of them had issues. A little TLC and they can become great runners.

dale
February 7, 2024 at 7:57 pm #284740
reivertom
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US Member
If you can get it to fire and run long enough to heat up, it might loosen up the rings if they are just stuck compressed. Make sure it is pumping water during this. After that, check it again. You might even put some penetrant down the spark plug holes and let it sit over night before hand. I also put some Sea Foam in the gas/oil mix to try to de-gunk things. It has worked for me several times.

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The Boat House
February 7, 2024 at 8:20 pm #284742
crosbyman
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Canada Member - 2 Years
change impeller and gear oil … if water in the GC … a reseal is in order ! but for run just refill…. you can take care of the GC later

Joining AOMCI has priviledges 🙂
February 8, 2024 at 4:09 am #284743
elgin2
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US Member
Installed seal last night. Will clean up points and see if it will fire. Probably will go through the carb too. Everything under flywheel was newer but it still had j4j plugs in it.
February 8, 2024 at 5:27 am #284744
Fastwin18
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International Member
Mine is a 1960 too, the compression below was measured after a full rebuild, including new rings.

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David Bartlett
February 8, 2024 at 7:35 pm #284762
mike n
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US Member
i agree with labrador guy. i have a 58 18 that i got running last summer. i didnt check compression but did all work to get it fired up. it started but ran terrible for first few minutes. i wonder if reed valves were stuck from dried up fuel oil mix or stuck rings , which i guess could cause low compression when checking. mine cleared up after a few minutes of running and runs great now. even if you had trouble with the powerhead, it isnt too difficult to find another for that motor.

mn
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