The Spark Plug Story

RenkenII

Seaman
Joined
Jun 13, 2011
Messages
53
Mercruiser 470 / 3.7 1985 - 1987 S/N 779810. I have had no running issues lately, but decided to change the cap, rotor, wires and plugs. (never did the wires since I owned the boat) Upon removing the plugs, which I changed the spring of 2011, I found them burning in this fashion:20130705_211156_resized.jpg What story do they tell? The plug on the left was in the front of the motor(#1) and the right plug was in the back fo the motor (#4). Thanks for your time. It is a very smooth and powerful motor. I have done a tone of stuff and am hoping I'm not on my to a head gasket repair:facepalm:.
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,583
Re: The Spark Plug Story

No 470 guru here but, I don't see it as a head gasket, looks to me like yur burning oil on 4 and some on 3.
 

bonzoscott

Senior Chief Petty Officer
Joined
Jul 26, 2008
Messages
745
Re: The Spark Plug Story

Compression test with particular attention to 3 & 4 numbers. If compression is good, likely worn valve seals. They don't look that bad and if compression is good, I wouldn't sweat it just yet.
 
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