No compression in 1 cylinder on 5.7 merc help

[fdwengen]

I have a 1995 Mercruiser 5.7 Had rough Idle did a compression test read as follows
#1-170
#2- 179
#3-30
#4- 185
#5- 0
#6-186
#7- 168
#8- 170
What could be the problem, could it be just the valves?
Engine runs can still do 4000RPMs normal up to 4500, still does 33MPH normal up to 38. Oil clean, no abnormal noise except rough idle.
New engine or valve job?

 

[Bt Doctur]

Re: No comprssion in 1 cylinder on 5.7 merc help

Re: No comprssion in 1 cylinder on 5.7 merc help

water ingestion from a bad riser/manifold hung up a valve
broken valve spring leaving the valve open, bent valve
lifter/pushrod issue
cam lobe gone
holed piston from a lean condition.
pull the valve cover to check spring heights, using a hammer tap the rockers,
solid=stuck
soft and returns=ok
crank engine to see if all rockers move
remove head to check for burnt/tuliped valves, piston damage

 

[Don S]

Re: No comprssion in 1 cylinder on 5.7 merc help

Re: No comprssion in 1 cylinder on 5.7 merc help

You could go to all the trouble to do a leakdown test to determine what the problem is, but the fact is, you still have to pull the head to fix it. Might as well pull it and look, then you will know for sure what the problem is.
Usually a blown head gasket will not drop the compression down to 0.

 

[Bondo]

Re: No comprssion in 1 cylinder on 5.7 merc help

Re: No comprssion in 1 cylinder on 5.7 merc help

Ayuh,...

Even though #3,+ #5 are next to each other,...
I agree with Don,...
A Blown headgasket usually will yeild more than 0 psi compression....

That motor has some Serious issues that need to be dealt with.....