Merc 140 Low compression on 2 and 3.

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hanagansny

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Apr 17, 2012
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I have a 84 CC scorpian with a Merc 140. Had it out running well then out of the blue no power. Got the boat back to my dock checked the normal things and found water in the oil. Did a compression test #1 had 120, #2 had 45, #3 had 49, #4 had 110. To me this is a head gasket. This is the first 140 Ive owned. There was no sign of over heating never seemed to even get hot. Could this be just a gasket or do these heads warp or crack easy? Any help would be great.
 
achris

achris

More fish than mountain goat
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27,468
Re: Merc 140 Low compression on 2 and 3.

Heads crack, yes but usually at the exhaust port, not across 2 cylinders. Doesn't matter, you've got to pull the head anyway, so you'll find out once it's off.

Welcome to iBoats BTW.. :D
 
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stonyloam

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Re: Merc 140 Low compression on 2 and 3.

Adjacent cylinders with similar low compression #2-45,#3-49 are a symptom of a head gasket blown between the two. +1 pull the head.
 
Bondo

Bondo

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Re: Merc 140 Low compression on 2 and 3.

stonyloam said:
Adjacent cylinders with similar low compression #2-45,#3-49 are a symptom of a head gasket blown between the two. +1 pull the head.
Click to expand...

Ayuh,.... Ditto that, x's 2....
 
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dubs283

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Re: Merc 140 Low compression on 2 and 3.

i've always found that with two adjacent cylinders having low or zero compression the isuue is 9 times out of 10 a head gasket failure between the two cylinders

had to say it...;)
 
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hanagansny

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Re: Merc 140 Low compression on 2 and 3.

Gasket broke between 2 and 3. That explains the compression problem. Alot of rust in the intake ports of 3 and 4. Cant see any crackes in the head or the gasket where water could get in the oil. Didnt want to but the head will have to go to the machine shop to get checked out.
 
Bondo

Bondo

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Re: Merc 140 Low compression on 2 and 3.

Ayuh,.... How Much water was in the oil,..??
 
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hanagansny

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Apr 17, 2012
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Re: Merc 140 Low compression on 2 and 3.

Enough to turn new oil very milky. Not enough to raise the level on the dip stick alot. I did read on another thread about the exhaust flapper and water in the engine. Mine is totaly gone I found out today. Could that flapper being gone be the water problem? I do leave the boat in the water full time.
 
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dubs283

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5,099
Re: Merc 140 Low compression on 2 and 3.

a missing/faulty water shutter would cause the engine to hydrolock and be difficult or impossible to turn over until the water is cleared from the cylinders

unless the piston rings are completely shot there is little chance of water in the cylinders entering the crankcase/oil pan

something is causing the cooling water to enter the engine oil while running, perhaps a cracked head due to overheat
 
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