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water damage in cylinders - try to turn it over or pull and rebuild?

A

ants

Member
Hi,

Found water in cylinders on one bank of a Merc 4.3 EFI, it was a few days between last running it (ran ok, and shutdown normally) and finding the water due too not turning over. I got the water out and flooded each cylinder with wd40 and left to soak for a couple of days, and now inspected with camera, clearly some surface rusting on cylinder wall:

WIN_20210108_16_21_16_Pro.jpg

I cant turn it over by hand with socket on crank so far (but I am not turning it as hard as I could as I dont want to sheer the belt pulley bolt, but turning it harder than it would normally take).

Do I flood it with more wd40 or oil and then try to turn it over with the starter and presuming it turns over do a compression check? I could take head off and try to clean cylinder walls up but that doesnt fix up piston rings etc and not much more I can do without lifting boat out, craning engine out and stripping it down, and if the cylinder walls are damaged then I am guessing it will need boring and oversize pistons anyway so does it do any harm to see if it can be turned over as is and if it does then after an oil change try to start it? Or if piston rings are corroded will it effect the oil in the cylinders and potentially do lots of harm?

The oil in the rockers is milky, oil in sump is not, so looks like water got in (presuming thru exhaust) at last shutdown (ill remove exhaust to check and fix before trying to start).

Basically it is middle of summer here in Australia and I am not sure whether to just try to get it runiing and if it works use it until winter, or if it even worked that will likly do more damage and have to bite the bullet and rebuild it out now (I have rebuilt engines before so not worried about doing it, just bad timing and limited parts availability at the moment here at short notice)

Thanks

Ants
 
Here is the question you gotta ask yourself: Does this engine give me 100 percent confidence that it will both get me to my destination and safely back home without any problems? If the answer is no, then you know what you must do.

It doesn't appear that the damage is severe. It takes a surprisingly small amount of corrosion to lock up the engine. Perhaps you can get away with disassembly, quick hone of the bores, new bearings and seals, a set of rings and back together again. Still, that's a significant amount of work and down time.
 
Remove all the sparkplugs, crank engine over to clear the cylinders,
Try to dertermine how water entered. cracked block, leaking manifolds, elbow. If "Batwing manifolds" replace them .
Remove hoses going to the manifolds , hokk up water, and fire up the motor to dry everything. You can run the motor a minute or two without damage
 
WD 40 will displace moisture but fogging oil will do a better job of lubing the cyls if you want to try to crank it over with the starter with the plugs out. I had salt water in one cyl but got it out fast & fogged it repeatedly so I did not have rust in the cyls when I pulled the cyl heads (blown head gasket, wound up replacing cyl heads). I replaced the heads installed new exhaust (even though my OMC batwings were not leaking, they were in use 6 years which is close to the limit for salt water) and its still running well 3 years later.
As noted above, if you had the Merc batwings that could be the source of the water, any overheats in the past?
 

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Hi,

Given it was 3 cylinders on one side I am guessing the source of the water is the exhaust but I will of course take it apart to check, they are about 6 years old now so about due to be replaced. I have twin engines so whilst not ideal, I can get home on one if this engine turns out to be unreliable and in need of further work. Have left it soaking a bit longer in more oil and will try to turn it over and do compression check and see if it will run etc. I figure if there is pitting then it is already there by now and will need rebuild anyway so if it runs ok in the meantime then might as well use it and plan full rebuild in winter.

Thanks
 
Ants, because this is a V engine, any oil or fogging solution (introduced into the cylinders) is going to pool at the low side of the cylinder (gravity takes over).

In my opinion, your best bet will be to get this engine started up ASAP.
Allow engine heat to evaporate any residual moisture.
Examine the engine oil.

As Bt Doctur says in post #3, you can run the engine for a short duration without cooling water.
Be careful as to not allow exhaust heat to damage the interior of your rubber exhaust couplers.

Do not operate the engine without water to the seawater pump (assuming you have the A drive).

The seawater pump's supply to the engine can be diverted by disconnecting it prior to the T-stat housing (raw water cooled engine), or at the seawater intake at the Heat Exchanger (closed cooling system).

Or, remove the drive (again, assuming that you have the A drive!)

Important part being.... get it fired up ASAP.


Now you can move on to your discovery options:

Cylinder pressure test
Cylinder pressure leak-down test
Exhaust manifolds
Etc.


By the way, use extreme caution if you attempt to turn the crankshaft over via the center bolt.
This bolt may snap if you come up against too much resistance and/or exceed the prescribed torque rating.

If it was to snap, you'll be pulling the engine and taking it to a machine shop for a professional bolt extraction.


.
 
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