1994 Johnson 140 Oceanrunner uneven compression

G

gksail

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Well, I just got the bad news from the mechanic at the marina. He tells me I have one cylinder with no compression and I need a new powerhead. I never used this mechanic before and he seemed a little quick to determine I needed a power head. I have searched this forum in length and all suggests you need to pull the head to check head gasket. I brought boat home and did a compression test on my own to find

Port side top Cylinder 90#
Port side 110#
Starboard top 70#
Starboard bottom 110#

Do I have 2 bad cylinders? What should be my next step? Should I pull the heads on both sides or starboard or just give up on this one??
 
V

Van Wildonher

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Aug 15, 2009
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Re: 1994 Johnson 140 Oceanrunner uneven compression

I think the 70 is low... 90 might still be ok. Did you let the engine warm up before doing the test? Did you have the spark plugs in the other cylinders while doing the test?

Why do you say that you think it's a little soon to say you need a new powerhead or rebuild. If the facts are there, which they seem to be then it's sure possible.

I'm not sure about the head gasket, somebody with more experience will have to answer that one.

Edit: Did he say NO compression or LOW compression?
 
tashasdaddy

tashasdaddy

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Re: 1994 Johnson 140 Oceanrunner uneven compression

try a different gauge. they all read differently. i would do a decarb if the motor will run. then recheck the compression. if you still have the difference, then pull the heads.
 
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gksail

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Re: 1994 Johnson 140 Oceanrunner uneven compression

Van Wildonher said:
I think the 70 is low... 90 might still be ok. Did you let the engine warm up before doing the test? Did you have the spark plugs in the other cylinders while doing the test?

Why do you say that you think it's a little soon to say you need a new powerhead or rebuild. If the facts are there, which they seem to be then it's sure possible.

I'm not sure about the head gasket, somebody with more experience will have to answer that one.

Edit: Did he say NO compression or LOW compression?
Click to expand...

Thanks - He said NO compression (maybe why I questioned the quick decision to rebuild)

I did the test with the plugs in and engine was cool.

He may certainly be right to say it needs a rebuild, I just wanted to make sure all the fact are truly in
 
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gksail

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Re: 1994 Johnson 140 Oceanrunner uneven compression

tashasdaddy said:
try a different gauge. they all read differently. i would do a decarb if the motor will run. then recheck the compression. if you still have the difference, then pull the heads.
Click to expand...

Decarb complete recheck shows

70 now 90

so I have 90-110-90-110
 
B

boobie

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Re: 1994 Johnson 140 Oceanrunner uneven compression

This may sound stupid to a lot people on this forum but try another decarb and then check the compression again. I had a mtr that was put away with out winterizing and sat for three yrs. Wouldn't idle so after four cans of engine tuner, letting it soak properly, the idle came back and mtr ran fine.
 
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gksail

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Nov 22, 2009
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Re: 1994 Johnson 140 Oceanrunner uneven compression

boobie said:
This may sound stupid to a lot people on this forum but try another decarb and then check the compression again. I had a mtr that was put away with out winterizing and sat for three yrs. Wouldn't idle so after four cans of engine tuner, letting it soak properly, the idle came back and mtr ran fine.
Click to expand...

I wondered about that - Was going to try it definitely will now.
 
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boobie

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Re: 1994 Johnson 140 Oceanrunner uneven compression

If you would, post back the results.
 
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