Water in the cylinders

[warefuller]

Short version: Water comes out the plug holes on #3 and 4 (when cranked with the plugs out). Manifold does not leak, at least at 3 psi. Removed the head-gasket, and head and gasket look like new (had the gasket pair replaced last summer). Head is flat. No water in oil.
Other than a cracked block (pray no!), how else can the water get into the cylinders?

Long story:
1. Engine usually purrs like a kitten - starts after 2 revolutions, but still turn off water before starting.
2. Engine runs cool - around 130 F.
3. A week ago I started the engine and it ran extremely rough and wouldn't take any throttle, I checked the usual suspects, fuel and spark. While checking the spark, with the plugs out, is when the water geysers from #3 and 4 happened. Sh...., the head gasket again, I thought.
4. So I pulled the head and found the gasket and head in good condition, with no evidence of a water passage from the cooling channels to the cylinders (water leak usually causes a rust line on the head, but perhaps rust hadn't had time to form - pulled the head 2 days after problem occurred).
5. Checked the manifold using the plug-and-blow technique - no apparent leak. An aside: I once measured the pressure I can blow (about 2 psig) and suck (about 3 psig). Could the leak be so tiny that in only occurs with the higher pressure coming from the water pump? A stretch, I think.
6. Engine is a newer type and I have a Moyer anti-siphon valve installed. Probably should take it off and check its operation.
7. Six of the studs came out and I noticed that the nuts were pretty corroded on them. Also noticed that the threads on the bottom of the studs is much coarser than the nut end. Could it be that when the studs were torqued to 30 ft-lbs, only the coarse threads were turning (nut frozen to the stud)? That would put a lot less axial force on the stud. Would love to believe this was the problem.

Am putting the head back on as soon as the gaskets and some studs arrive, and only half- expect the problem to be solved.

So, what am I missing?
Would appreciate help.

Ware

[The Garbone]

How many threads are left on the bottom of the studs? The interesting thing it is both 3 and 4.. I had a perforation on 3 and with the exhaust off and the engine running it acted like a water pump. Depending on the position of the piston when you did your blow test this could still be it but for the water from 4...

i would rotate the motor by hand and look down the bores.

[warefuller]

Thanks Garbone.
Not sure I understand some of your reply:

"How many threads are left on the bottom of the studs?" 5 or 6. Why?

"I had a perforation on 3" Where? In the head, the block, the manifold?

"with the exhaust off and the engine running it acted like a water pump." You mean the exhaust pipe was disconnected at the manifold outlet? Where did that water come from? Inside the manifold? On my engine the cooling water comes out of the thermostat, goes into the manifold, then exits the manifold on the top, and goes to the mixer (way downstream in the exhaust).

"Where Depending on the position of the piston when you did your blow test" How does the piston position matter?

"this could still be it but for the water from 4..." I don't understand this comment.

"i would rotate the motor by hand and look down the bores." I have done that briefly and will do it again. I presume I am looking for a crack in the cylinder wall. Yes?

Ware

[hanleyclifford]

When you get the engine back together do a pressure test of the cooling jackets, block, head and manifold all together. If the engine will hold 20 psi you are good. If the engine fails the test, test the manifold separately and hope it fails.

[Dave Neptune]

As per Hanley check the block for leaks. I am going to guess that since the engine runs well and did so before the water that hopefully you just had an "anti-syphon" failure.

Do you turn off the water valve when cranking?

Hopefully this is just a simple fix. Other than what has already been disassembled.

Dave Neptune