Water in cylinder bore

[Coxy1954]

Hi, I was happily running my old Draco Sterling last year with no engine problems. I arranged for the local boat yard to winterise her. They reported some engines problems and suggested a compression test resulting in the middle cylinders showing little to no compression. I have had the cylinder heads off and the middle bores have had water in them and the piston rings are seized. The heads aren’t cracked and the head gaskets are fine. Does anybody have any ideas as to how this may have happened? Any help appreciated, The engines are Mercruiser 4.3 V6. (1992).

 

[Pete7]

At a guess its the exhaust risers that are shot and allowing water to flow back into the cylinders. On 30 year old engines with water in them you are probably looking at replacing the blocks and heads. Have a chat with the lads over on boatmad:

Boatmad.com

 

[RichardS]

Pete7 may well be correct. Also, if the engine has been turned over for too long without firing then water might well find its way through the exhaust valves into any or all cylinders. However, water in just one cylinder is more likely to be an gasket failure but water in two could be either cause.

Richard

 

[Moodysailor]

Another vote for manifolds/risers being the cause. It's fairly common, so I would start the investigation there. I always hated those cast designs, the gaskets have as much chance of leaking internally as externally.

 

[Coxy1954]

The risers and manifolds were replaced about six years ago. I’ve pulled the heads off and the water is only affecting the middle cylinders. One exhaust valve is rusted open. Why only middle cylinders? All gaskets seem fine. The other engine is also low on compression on middle cylinders.

 

[Bilgediver]

The risers and manifolds were replaced about six years ago. I’ve pulled the heads off and the water is only affecting the middle cylinders. One exhaust valve is rusted open. Why only middle cylinders? All gaskets seem fine. The other engine is also low on compression on middle cylinders.

The exhaust valves were closed on the other cylinders . Or maybe adjacent inlet valves open allowing water from one filled cylinder to flood to the next via the inlet manifold.

 

[jwfrary]

Unfortunately 6 years isn’t an abnormal amount of time for them to last

 

[Coxy1954]

Thanks all, it certainly looks like the likely cause. I notice on ebay US site aluminium manifolds and risers are available. I’m not sure that they will fit my old engines. Does anyone have any experience of fitting them.?

 

[spannerman]

We have a Draco in right now with the same engine and same problem, water in the cylinders, on this engine it was because the exhaust shutters were broken allowing water to flood up the exhaust on deceleration, its an item people forget or not aware of. And some boats are more prone if the engine is low down in relation to the water line and riser extensions are not fitted due to space limitations, which is a bad installation IMO. My own Draco has a Magnum 350 from 1996, although I rebuilt it last year, and I have SS risers which are also’96 with freshwater cooled manifolds so the complete exhaust system is as good as new after 25 yrs!

 

[coopec]

Is the water salty or fresh? Can you tell?

 

[Graham_Wright]

Interested in learning about the engine, I did a net search with the following offer;-
Two engine types have been built to date: Draco and SuperDraco. The original Dracothruster is a small rocket engine for use on the Dragon spacecraft. SuperDraco is derived from Draco, and uses the same storable (non-cryogenic) hypergolic propellant as the small Draco thrusters, but is much larger and delivers over 100 times the thrust.

Perhaps something different