johnson 115 81model compression

hypo069

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Apr 19, 2010
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Hey guys i have a 1981 model johnson 115hp, i recently did a compression test- left side - 120, 118, right side - 115, 107,,,,does this sound bad?
 

kenmyfam

Supreme Mariner
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Aug 10, 2006
Messages
14,392
Re: johnson 115 81model compression

Should be even and within 10% of each other. Give it a decarb and check it again.
Welcome to iboats
 

hypo069

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Apr 19, 2010
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Re: johnson 115 81model compression

I just put oil into the cylinder that is low 107psi and it read 115psi, after testing that cylinder about 5 more times it went back to 107psi so i presume i have a worn ring? any suggestions
 

SparkieBoat

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Aug 17, 2009
Messages
3,643
Re: johnson 115 81model compression

do a decarb..instructions in the secret files section at top of forum..if that does not work you can try resurfacing the head and replacing head gasket.
 

kenmyfam

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Joined
Aug 10, 2006
Messages
14,392
Re: johnson 115 81model compression

I just put oil into the cylinder that is low 107psi and it read 115psi, after testing that cylinder about 5 more times it went back to 107psi so i presume i have a worn ring? any suggestions

May just be a "sticky" ring. Decarb as suggested and re-check
 

emdsapmgr

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Dec 9, 2005
Messages
11,551
Re: johnson 115 81model compression

120 to 125 was probably normal compression when it was new. These crossflow engines are prone to accumulating carbon around the rings as they get older. Carbon buildup will affect (lower) the compression readings. I'd follow all the prior suggestions about doing the decarb before you get too concerned about the compression readings. If needed, a second decarb may help further. The decarb process should also improve the idle characteristics and improve cold starting. It is also typical that the compression on these crossflows can vary 5-8 lbs between the two heads-due to the way the blocks were originally manufactured.
 

hypo069

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Apr 19, 2010
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Re: johnson 115 81model compression

Cheers guys, you have been very helpful, i will be doing a decarb on the w/e and will let you's know how i went.
 
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