Seized cylinders - zero compression

[KeithD]

Hi,
I'm having some serious engine problems with my boat. It's a 2000 310 - with the 350 Mag I/O's. It's running rough, and there's a smell of gasoline from the exhaust.
We had a compression test performed. I'm getting zero compression from one cylinder on each of the port and starboard engines.
Time for a valve job? The boat has new risers and manifolds installed a year ago, just prior to us purchasing the boat.
Any thoughts advice or opinions are welcome.
Thanks

 

[H2ONUT]

The 2 cylinders with "0" compression, spray some WD-40 in those 2 cylinders and see if you get a reading.

Being that you smell fuel, I would guess that an exhaust valve is stuck open.

How are the readings on the other cylinders?

 

[unlvrebel]

Sounds like collapsed rings. Is there fuel in your oil? If something was seized then you wouldn't run unless the rods had become disconnected. But then you would have an awful racket...

 

[SloppyJoe]

Remove the rocker arm covers and the coil wire on each engine, crank the motor and watch the valve train carefully, especially on the zero compression cylinders. You should be able to identify which valves are not opening. You can also clarify whether you have bent connecting rods without removing the oil pan by removing the spark plugs and checking that each cylinder reaches TDC. A bent connecting rod will not reach TDC.

My guess is you had water ingestion in each engine (probably at the lowest/aft cylinders) causing possibly damaged valve train (bent/broken push rods, broken rocker arms, etc.) If you are lucky this is all the problem is. You can check and replace any bent push rods or bent/broken rocker arms without removing the intake manifold. If the lifters pump oil up through the push rods when running warm they are probably OK; any that are not may be collapsed.

Most importantly you need to look at the layout of your exhaust system to see why this happened and fix it so it does not happen again.

 

[J Levine]

This year and model is well know for water ingestion issues especially if the exhaust system has not been upgraded to the water lift mufflers

 

[fc3]

Remove all spark plugs. Alter your compression tester by removing the gauge and connecting the hose such that you can connect it to your air compressor. Most have fittings so this is easy. Remove the schrader valve from the end of the compression tester hose. Uncap the oil filler.

Turn the engine until you see the piston at TDC though the plug hole. Attache the compression tester hose connected to the air compressor. Introduce 100 psi air into the cylinder from the compressor. If air leaks from the intake or the exhaust, turn the engine one full turn via the damper pulley until the air flow stops. It it does not stop and you have significant leakage from the exhaust side, you have a bad exhaust valve. Leaks from the intake indicate a bad intake valve. It minimal leakage from the intake or exhaust but a lot of leakage from the oil filler means bad compression rings.

Repeat for each cylinder. You can save yourself some engine turning by following the firing order.

Best regards,
Frank C

 

[FireIsland1]

That year was a lot of trouble for Merc. Valve overlap and low idle caused a mist of water to enter all the cylinders. Most boats got away with problems for a long time. some like mine died after a few hours. When the dealer opened my engines after 18 hours, they looked like they were under water.