1979 Johnson 150 V6 Low Compression

bartowair

Cadet
Joined
Aug 21, 2008
Messages
13
Ive been working on this motor and found low compression on one of the cylinders , 90 on one -120 across the rest . My question is " can just one cylinder be worked " ? And how difficult is the process. Ive got a SELOC Manual to go by , not very detailed in this area.
 

JB

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Mar 25, 2001
Messages
45,907
Re: 1979 Johnson 150 V6 Low Compression

Do a decarb first. Then take compression again. If that cylinder doesn't come back pull the head and inspect the head gasket.

Low compression is not an assured mechanical problem.
 

ksubigbuck

Petty Officer 2nd Class
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Aug 18, 2006
Messages
180
Re: 1979 Johnson 150 V6 Low Compression

By decarb, he means remove the carbon build-up from inside the cylinders. Do a search for "decarbing an engine" for the dirty details.
 

emdsapmgr

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Dec 9, 2005
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11,551
Re: 1979 Johnson 150 V6 Low Compression

Not sure what you mean by "work" on one cylinder. If you mean to bore oversize, the answer is yes. Depending on what you find when you tear it down, you may not need to bore it. The 79 engines all used high ring pistons. These high ring pistons provided great compression at the time, but were prone to fail rings due to carbon around the rings. The annual "decarb" on these early crossflows was important for this reason. Once you loose compression on one hole, you are probably looking at a teardown. I'd pull the head and side bypass cover on the low compression side and have a look. I'd get hold of an original factory manual from OMC-specifically for that year. You can contact Ken Cook co, in Milwaukee to get a copy.
 

bartowair

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Aug 21, 2008
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Re: 1979 Johnson 150 V6 Low Compression

Thank you very much for explaining the decarb, Ill will be getting to my boat mototr in the morning and Ill post my findings. Thank you
 
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