Rust On Spark Plug

[rusty bolts]

1987 460 FORD OMC I think its a valve or head gasket . or both The compression on two adjacent cylinders are at 110 ONE CYLINDER COMES UP WITH A LITTLE OIL to about 120 the other stays the same .The others cylinders are all close to 135 . ther is no water in the oil .Would you think head gasket or and a bad valve .The motor will go pop pop once in a while i was told that the valve will turn when running and may have a carbon on or i think rust because of water either way is it time to pull it apart ? if so what will be looking for Thanks for any input

[Don S]

Probably bad exhaust manifold or riser, or the connection between them.
Water leaks into the manifold exhaust passages and into cylinders with open or leaky valves.
Common problem on marine engines.

[rusty bolts]

Thanks I did change the riser gasket this season using omc gasket sealing compountd and it did drip after i ran the boat for the first time > because it was leaking out side the riser . I will replace riser gasket and exaust mainfoil gasket.Would a bad mainfoild gasket ,where it meets the block cause it to get in cylinder? i guess only if the connection between riser and mainfoild was bad. The riser looked reel good wiith little rust since it has been a freashwater boat most of its life only 3 seasons in salt. Temp never goes over 154 and idles a 140 or so .If the gasket is bad {conection between them ]that wou;d be great mainfolds for are $700 apice i can still get them.

[Gary H NC]

If the riser gasket was dripping on the outside then chances are it was leaking on the inside too..
I would replace that gasket first and give it a test run.
Be sure the mating surfaces are clean and rust free where the riser meets the manifold.Use a straight edge to check to be sure its flat too..

[rusty bolts]

It was leaking (as seen in the photos) any advice on how to fix the gasket would be helpful.
http://img.photobucket.com/albums/v7...i/DSCF3341.jpg
http://img.photobucket.com/albums/v7...i/DSCF3345.jpg
http://img.photobucket.com/albums/v7...i/DSCF3337.jpg
http://img.photobucket.com/albums/v7...i/DSCF3344.jpg
http://img.photobucket.com/albums/v7...DSCF3342-1.jpg
Thank-You