Low Compression On One Cylinder

[JASONDEEP]

I Have Two 1995 Merc Black Max 200 On My Boat I Went Out On The Boat This Past Weekend And Had A Problem With The Power Pack On One Of The Motors 3 Dead Cylinders With No Spark Replaced The Power Pack And That Fixed The Spark Problem But When I Checked
Compression Had 130 On All Cylinders Except For The Top Cylinder Had 65 The Thing That Is Strange Is When I First Checked Compression The 3 Cylinders That Gave Me Problems With Spark All Showed 65 Then 2 Cylinder Went Back To 130 After Checking Several Times...but I Still Have The Top Cylinder Showing 65??not Sure If Its A Bad Piston Gasket Or What It Is??cylinder And Piston From What I Can See Apears To Looks Ok..

 

[Windykid]

Re: Low Compression On One Cylinder

You might try a decarb and check again.

 

[JASONDEEP]

Re: Low Compression On One Cylinder

Thats My Next Step Thanks For Your Help.

 

[gss036]

Re: Low Compression On One Cylinder

If you can find SeaFoam "DEEPCREEP" in a spray can use that. Most NAPA/Shucks, Auto Zone etc, stores carry it.Spray a generous amount into the cylinder and let it sit and soak for 24 hours. Might just have a stuck ring. Then do a full decarb. FAQ has the formula for and instructions for one can SeaFoam to 3/4 gal.

 

[JASONDEEP]

Re: Low Compression On One Cylinder

Well Tried The Decarb With No Luck Followed All The Steps But Still 60 Pounds Decided To Pull The Head Out And Noticed The Gasket Had A Bad Spot Cylinder And Piston Looks Ok Time For New Gasket Found Out Thermostat Was Stuck Not Allowing Water Flow

 

[Windykid]

Re: Low Compression On One Cylinder

Change thermostats and head gasket, you should be good to go.

 

[JASONDEEP]

Re: Low Compression On One Cylinder

Well Just Replaced The Head Gasket And Turns Out That The Compression Is At 95 On All Cylinders My Compression Was At 125
Before All My Problems Started The Only Thing I Can Think Of Is That My Batterys Might Be Weak Not Allowing The Motor To Turn Fast Enough To Get A Higher Reading On The Guage The Motor Runs And Sounds Good My Only Concern Is If It Is 95 IS THAT OK?thanks For The Help..

 

[ohbubbabob]

Re: Low Compression On One Cylinder

A low battery gave me compression values that kept going lower with each re-test. With new battery, values were perfect. Also make sure throttle is wide open when testing.