Mercruiser 260 rebuilt - Water in cylinders and oil?

Hey Guys, got a quick question for the guru's here...

I just finished putting back together my 260 from a complete rebuild. I was able to fire it up and get it running nicely on the test stand. After shutting it down for a couple minutes to adjust the timing it was hydrolocked. I cleared the water out of the cylinders, retorqued the manifolds and got it running again. Ran it for 20 minutes to complete breakin and shut it down. When I tried to restart it, same problem, hydrolocked...

Before test firing, I put new risers on it and cleaned up the older manifolds. They seemed to be in pretty good shape, not original.

Other than water pouring into the cylinders and oil pan, the rebuild was a success. I am so glad I test ran it on the stand and not in the boat!

So... I pulled the exhaust manifolds/risers and put water to em, looking (hoping) to see water pouring out of the exhaust port, but none did, not a drop. I haven't pressure tested them yet as they "seem" to be solid. I was hoping to get pointed a different direction to find the massive water leak. Even with no pressure on the cooling system,water still flows/fall into all of the cylinders causing hydrolock. I even pulled the intake mani off to see if it was rotted out, it was not. There was some internal rust/corrosion and there may be some leakage there but not enough to fill a cylinder in 3 minutes with no pressure in the cooling system.

I am hoping to not have to pull the heads back off to check the gaskets as it seems that that amount of water shouldnt be able to pour through a failed gasket that quickly, without pressure and on both heads...

Block was checked at the machine shop as were the heads...

I'm stumped on this one...

Anyone?.... Anyone?.... Beuller?

Re: Mercruiser 260 rebuilt - Water in cylinders and oil?

Since you have the manifolds off, fill them with acetone instead of water. Look for any leakage.

Re: Mercruiser 260 rebuilt - Water in cylinders and oil?

Were the head bolt threads sealed?

Re: Mercruiser 260 rebuilt - Water in cylinders and oil?

wrong gaskets on the risers? If it didn't freeze and break in 2 places nothing else is in common with all cylinders that I can think of.

Re: Mercruiser 260 rebuilt - Water in cylinders and oil?

I did not do anything special on sealing the head bolts, just a dab or oil to lubricate them. The bolts dont go into the combustion chambers so even not sealed they shouldnt allow any water into the cylinders.

The risers came with new gaskets and they looked identical to the old gaskets that came off em. I'm not getting any water in the exhaust ports when I stick the hose to the water inlets...

The more I think about it, the more it seems like it has to be the intake manifold, but I pulled that off and ran water into the tstat housing opening and no water came out of the intake ports either...

I really hate the thought of pulling the heads and having to put new gaskets on again, but that's the only thing I havent pulled off yet...

I will keep tinkering with the exhaust manifolds and intake manifold to see if I can get some leakage.

Whats got me puzzled is the water in the cylinders... The combustion chambers should only have 2 paths into/out of them, the intake and exhaust valves (providing the head gasket isnt missing altogether)... Keep the ideas coming... I will keep messing with things until I figure it out or break something expensive... haha

Re: Mercruiser 260 rebuilt - Water in cylinders and oil?

just a thought, but you didn't put some kind of radical cam in it did you?

Re: Mercruiser 260 rebuilt - Water in cylinders and oil?

Head bolt threads enter the water jackets.

Re: Mercruiser 260 rebuilt - Water in cylinders and oil?

howdy,


Water in the cyls immediately after shut down, usually comes from open intake or exhaust valves and water in that respective area.........It's more likely EXHAUST instead of intake since intake water would probably cause an immediate hydrolock......AFTER shutdown, there's water in the riser above the riser gasket that could be leaking back into open exhaust valve(s). leaking during running wouldn't hurt anything since it would just be blown out with the exhaust........

Is it EVERY cyl or just a few? The same cyls or different ones each time?


You might pressurize the block and intake manifold before you pull it all apart (excluding the exhaust/risers) and maybe do a compression check (or better yet, a cyl leakdown pressure check) before you pull heads etc just to rule out head cracks/leaks......

You could also just isolate the water from the exhaust manifolds/risers and run the engine for a minute or so and see what happens.

Re: Mercruiser 260 rebuilt - Water in cylinders and oil?

Stock cam... well, I think it's stock. It was in it when I got the boat. I bought the boat with the blown motor. The motor that got thrashed was a recent rebuild from Jasper and it didnt have many hours on it. An exhaust valve shattered sending shrapnel through the motor scoring 5 of the 8 cylinders. The motor was punched 30 over prior to getting cooked. I had it punched another 10 over to fit pistons I had from another motor and had all the bearings etc resized and replaced.

I just did another leak test. With the intake manifold off, I filled the water jacket to the water holes in the heads (as full as I could get it, without water flowing into the valley). After 5 - 10 minutes the level was down and I had water is a couple cylinders again...

Now I AM hoping it's just something with a head gasket! Or even the heads! This block cost me a decent chunk o change to clean up and rebuild.... oye vey! and I was so proud of myself for making my first rebuild actually run well - which it does, until you introduce water or run more than 60 seconds... haha

Please let this be an incorrect head gasket or something cheap-ish!

I guess the heads will be coming off in a few minutes. :-(

Re: Mercruiser 260 rebuilt - Water in cylinders and oil?

I just finished putting back together my 260 from a complete rebuild.

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Ayuh,... Define a complete rebuild....

What work was done to the Heads,..??

Re: Mercruiser 260 rebuilt - Water in cylinders and oil?

Bond-o said:

Ayuh,... Define a complete rebuild....

What work was done to the Heads,..??

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They were hot tanked and the exploded exhaust valve was replaced. They also cleaned up the valve seats and put new valve seals in...

I just pulled the starboard head off, water in the cylinders (all 4) and the gasket looks great. No sign of leaking from the gasket.

Cylinder walls look great too, no cracks that I can see and certainly nothing big enough to flow a quart of water in 10 minutes under very low (or no) pressure...

How can you pressure test a head? I dont have enough fingers and toes to plug all the holes and put water to it...

Edit: Oh yeah, complete rebuild was boring to 40 over, line boring the crank journals and resizing the rods to the freshly polished crank, new cam bearings, freeze plugs and maybe something else... approximately $900 worth of "stuff"... haha

Re: Mercruiser 260 rebuilt - Water in cylinders and oil?

You can put the manifolds back on with one bolt in the middle and two long bolts as guides. Run the engine till its warm. shut off and back out the one regular bolt and slide the manifolds out to the end of the long bolts and watch.

Re: Mercruiser 260 rebuilt - Water in cylinders and oil?

Overkill82k5 said:

I did not do anything special on sealing the head bolts, just a dab or oil to lubricate them.

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Out of the Mercruiser Manual #1, GM V-8 engines
Coat threads of cylinder head bolts with sealing compound and install finger tight.

Start the engine without exhaust manifolds on the engine.

Re: Mercruiser 260 rebuilt - Water in cylinders and oil?

Lyle29464 said:

You can put the manifolds back on with one bolt in the middle and two long bolts as guides. Run the engine till its warm. shut off and back out the one regular bolt and slide the manifolds out to the end of the long bolts and watch.

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Oh how I wish I could and wish I had thought of that earlier. I have it stripped down to almost a short block now, looking for the culprit...
and finding nothing obvious....

Re: Mercruiser 260 rebuilt - Water in cylinders and oil?

mkast said:

Out of the Mercruiser Manual #1, GM V-8 engines
Coat threads of cylinder head bolts with sealing compound and install finger tight.

Start the engine without exhaust manifolds on the engine.

Click to expand...

How can someone torque down the intake manifold with the heads only finger tight? Wouldn't the loose head bolts blow out the head gasket? I understand the sealer bit on the head bolts and I can see how that can allow water into the valve cover, but not into the combustion chambers... Unless I'm missing something here (which Ivery well could be, this is my first major rebuild)...

Re: Mercruiser 260 rebuilt - Water in cylinders and oil?

Overkill82k5 said:

How can someone torque down the intake manifold with the heads only finger tight? Wouldn't the loose head bolts blow out the head gasket? I understand the sealer bit on the head bolts and I can see how that can allow water into the valve cover, but not into the combustion chambers... Unless I'm missing something here (which Ivery well could be, this is my first major rebuild)...

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Lot of internet advice is great. Some is not.

Think he just didn't post the complete instructions . made a point then moved on.

Re: Mercruiser 260 rebuilt - Water in cylinders and oil?

Lyle29464 said:

Lot of internet advice is great. Some is not.

Think he just didn't post the complete instructions . made a point then moved on.

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Ahhh, right on. I always get multiple inputs before jumping into something unless it makes logical sense to me. Maybe it actually an instruction but not something I would try without much assurance since it's logically (to me) strange...

I did try to pressurize the head I pulled off by laying it flat on a piece of plywood, to seal off as much of the cooling passages that mate with the block, as I could. I flowed water heavily into one side and blocked the other with my hand and I detected no leakage from the intake or exhaust tracts... I may have to re-assemble everything just to test the different aspects of the cooling system to hopefully find the leak(s). It just seems wierd to me that both banks do it equally and I can see no reason why, even after tearing it down. Tomorrow I will put it all back together and pressurize the whole system wiht air and hopefully gain some insight... I get nauseous thinking about all that water sitting where oil is supposed to reside...

I will update when I get something figured out... Please keep the ideas coming. I'm definitley going to try Lyles method mentioned above to check the exhaust manifolds and risers...

Anyone heard of flushing an engine with diesel fuel instead of oil to clear out water from the system? Just a 30 to 60 second run, then change - repeat, then put fresh oil in? Diesel would be much easier on the wallet, but I dont want to cripple my baby any more than I have already...

Thanks for the ideas so far, you guys do indeed rock!

Re: Mercruiser 260 rebuilt - Water in cylinders and oil?

It just seems wierd to me that both banks do it equally and I can see no reason why,

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Ayuh,... That would lead ya to think, Intake manifold...

Anyone heard of flushing an engine with diesel fuel instead of oil to clear out water from the system? Just a 30 to 60 second run, then change - repeat,

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Nope,... Don't start it...
Flush it if ya want,...
Maybe turn it over on the starter,...
But Don't start it...

Re: Mercruiser 260 rebuilt - Water in cylinders and oil?

Ok, I will not fire it on diesel. Someone told me about it, but it seemed like a bad idea. I'm glad I asked.

I might have another intake manifold around here that I can try out. Of all parts I cleaned up from this motor, the intake was the worst looking piece. It cleaned up decent (exterior) so I reused it. I am sure hoping to figure this issue out today.

Thanks again...

Re: Mercruiser 260 rebuilt - Water in cylinders and oil?

Overkill82k5 said:

I am sure hoping to figure this issue out today.

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Try the Mercruiser maintenance manual, works wonders.