acceptable compression for 1984 Johnson 40 hp

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diamondlangus

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What would be considered good compression on this motor? Does anyone know the original specs for compression.
 

HighTrim

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Re: acceptable compression for 1984 Johnson 40 hp

I would think in the 100 to 140 psi range. Main thing is even between cylinders, within 10 percent for sure.
 

boobie

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Re: acceptable compression for 1984 Johnson 40 hp

What have you got for compression ?? Just curious.
 

diamondlangus

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Re: acceptable compression for 1984 Johnson 40 hp

The motor is on a boat I am looking at to buy. They said it is around 105 on all cylinders. I will have them test it with me there to verify.
 

gm280

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I don't know of any factory spec for compression on any OB engine. I know my factory shop manual for a '76 40HP Johnson gives every spec but compression. If your ring end gaps are in factory spec range, it will certainly have enough compression to make HP spec. if everything else is good. Obviously a bad head gasket can effect compression, but that withstanding, it will run good with everything else good. :noidea:
 

GA_Boater

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I just got back into boating this past week and picked up a 15'0" Astroglass w/ a 40 Johnson, 2-cycle 2-cylinder. I checked mine after the long test drive and it had 125psi on top and 123 on the bottom.

Inactive thread, over a year since the OP checked into the forums. {;ease start a new thread. Closed
 
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