? Water in cylinder testing

[RodMB]

In reply to a recent post regarding an engine that may not have been winterised someone offer this advice (amongst other things).

"It may not have a hand start........but can be turned slowly, manually with a little ingenuity ( pull the alternator drive belt, with the decompressor lifted) just to check that there is no water in the cylinder before starting."

I think the gist of this was by turning the engine over by hand with the decompression lever lifted you could check if there was any water in the cylinder.

I meant to ask at time how this works - i.e. what is it you are looking for when you turn the engine over by hand with the decompression lever lifted that would let you know if there is any water in the cylinders? It sounds like a handy test and I could do this fairly easily with my volvo 2002 which has both a decompression lever and a starting handle however I don't know what I'm looking out for!

Any thoughts much appreciated.

Regards

Rod MB

 

[Lakesailor]

On the compression stroke if you have more water in the cylinder than the volume of the compression chamber (including piston crown and exposed cylinder walls, for the pedantic) you will get a hydraulic lock. That is the piston will not be able to rise any higher in the cylinder due to the water in there. If turning by hand this is not a problem as you will simply not be able to turn it any more. If turning on the starter motor it probably won't be a problem as it will just stop the motor, although with a bit of a jolt.
If you had fired up the motor and other (less full) cylinders had managed a succesfull ignition, when the water filled cylinder locked up the motor, the rotational speed and flywheel effect would cause damage. Probably a bent con rod.

In other words if you can succesfully turn it over two full rotations by hand, you should be safe to carry on. It doesn't mean there isn't a crack or head gasket failure, but that at least it won't lock up.

 

[VicMallows]

But with the decompressor open, as original query, you won't get a hydraulic lock. I guess if there was any water it would end up in the exhaust, though probably also contaminating the oil. Bad but maybe not as serious as wrecking a con-rod. But I agree, how would you tell whether or not there was any water in there to start with?

Vic

 

[Avocet]

You might be able to take the injector out and try turning the engine by hand with the decompressor in the normal running position. If there is water in it, the water might squirt out of the injector hole but it depends how exposed this is.

I had a cylinder full of (sea) water after an anti-syphon valve failed once. I guess it had been there for about a week and the piston rings rusted to the bore. There was no way on this earth that the engine was going to turn over - not on the handle or the starter motor! I ended up taking th engine out and taking (it was only a single cylinder) the piston and barrel out with the piston still stuck in it!

 

[boatmike]

With DC lever depressed it will tell you diddly squat. If you suspect possible water ingress take injectors out and turn engine over with the starter motor with the sea cock shut to clear it before trying to start it.
Danger otherwise is if one cylinder fires before the other clears the water you could bend a con rod.