Likely cause of compression loss in cylinder 1

[400resto]

Hello,
I have only 30% compression in cylinder 1 of a four cylinder Mercruiser 3.0L 140hp 181 cid motor. ‘88 Celebrity
I was hoping a Cylinder Head Kit (Valves+Springs+Seals+Locks) could solve this problem or is the more expensive route of a New Cylinder Head (Direct Fit) is best. Or maybe im way off, thus this thread of mine. I thank you for your input.

 

[Scott Danforth]

there is no "likely cause"

you need to do a leakdown test to determine what is the reason

here are possible reasons (not in any particular order)

leaking exhaust manifold causing rusty valve or valve seat (if so, other valves may be close behind)
broken rings
hole in a piston from detonation (if so, other pistons may be close behind)
bent valve
cracked head
bad head gasket
cracked block

find out what is broken. then determine what course of action you want to go down to fix.

BTW, any 1974-1990 3.0 block and heads can be swapped in there. it will be a whole lot cheaper buying a rotten boat for the running motor than it would be to rebuild a 3.0. cost of properly rebuilding a 3.0 will cost you about the same as a 5.7 V8

 

[racerone]

Try setting valve lash first.

 

[kenny nunez]

Also could be a broken valve spring or the rocker arm stud pulled out on account of a stuck valve.

 

[400resto]

There was an exhaust manifold leak. It’s been fixed. I’ll check on the other possibilities. Thank You

 

[Scott Danforth]

There was an exhaust manifold leak. It’s been fixed. I’ll check on the other possibilities. Thank You

this could cause rusty valve seats
or bent valves or broken valves

the fix is to remove the head and have it serviced.

 

[Lou C]

That is one of the most common causes of inboard engine trouble. Water cooled exhaust leaks back into the cyls and rusts exhaust valve stems you get sticky valves, low compression and rough running. People don't realize that the exhaust system on an inboard boat has to be maintained just like the rest of it.