Water in the oil and low compression on 200hp Honda 2002

Our boat has twin 2002 Honda 200's. Last week I was 30 miles offshore and turned both motors off while drift fishing. When starting the Starboard motor the starter briefly loaded then turned over normally. The engine started but ran rough and seemed to have a knocking. I shut the engine down and pulled the engine cover to check. All appeared well, but there was water in the oil.

After checking the motor at home, #6 cylinder had 0 compression and cylinders 1 + 3 had 140-150 lbs of compression. All other cylinders were 190-200 lbs. Neither motor had SB#56 performed on it when this took place. I understand that #6 cylinder possibly ingested water and could have blown the head gasket. I'm not sure where the water in the oil is coming from? It might be a head gasket leak between 1 + 3, but not sure. I drained the oil/water and filled with new oil.

I have decided to either install a new short block or buy two new motors. The short block doesn't appear to be to terribly difficult and they are actually a reasonable price from Boats.net. So I'm leaning that way.

I really appreciate all the knowledge that I've gleaned off of this forum and I'm sure that one of you can help answer the following questions:

• What are the paths for water to mix with the oil...and how do I prove that is the issue? (Head gaskets, cracked head, etc, etc, etc)
• I have the factory service manual, which is very helpful, but is there anything special to watch out for when changing the short block?
• Will the new short blocks have better corrosion protection than the original 2002 blocks? (This block had bad corrosion near the Port side thermostat housing)
• I will perform the SB#56 mods, anything else that I need to do while performing this work?

Thanks for the help!

Good chance you'll be up for heads too, '02 is getting on and probably time to replace. If you have 0 psi compression it will more than likely be a valve, Honda V6 motors do occasionally corrode through in the exhaust port and the water would have got in past the rings. If the heads were okay you would have low compression, not no compression.

What you described is the classic issue that is addressed in Honda service bulletin #56. If you need a copy, send an e-mail to me at [email protected].

What happens is that kick back or reverse rotation on the engine occurs when the engine is turned off and a piston is near TDC of the exhaust stroke. With the piston moving backwards and the exhaust valve open, water is siphoned into the combustion chamber through the exhaust manifold and the open exhaust valve.

That causes hydro lock and will blow a head gasket or damage cylinders and valves. You won't know how bad the damage is until you pull the head.

The modified replacement exhaust pipes and oil pan gasket are designed to help prevent water from being siphoned into the combustion chamber when kick back occurs.