Testing piston rings with water

I have one of my two cylinder heads off and I was thinking of testing how much the piston rings are leaking. To do that, I was going to bring all the three pistons in that engine bank to the same vertical position (middle of the cylinder), then pour the same nominal amount of water in each combustion cavity (say 200-300 ml, or however much will fit), and wait some nominal amount of time (depending on how fast the water is draining) to see how much water is left in each cylinder.

The water would drain into the oil pan and not stay in the engine. As for the water remaining in the cylinders, I could suck it out with a syringe then wipe it off really well with a rag.

I am doing something similar for my valves: I set the head on bricks, put a receptacle under, and injected the intake (and will later do the exhaust) with 100 ml of water, checking to see how much is drained/left after 24 hrs. One of my cylinders is positively leaking (by 75% while others around only 20) and I preliminarily determined it was coming through the intake valves (by placing a hand on the manifold) but I want to do this test with the other cylinders to make sure they drain less water over the same amount of time before I get to lapping the problem valves.

My question is: Is pouring water into cylinder combustion space a bad idea?

 

Rust?

Have you performed a traditional pressure test?

 

Why the hell would putting water in a motor a good idea? Uhhhh how about OIL? Considering thats what will be in the motor while its running, not water. Shouldve leakdown tested the motor while it was together on a stand.

 

Using lightweight machine oil like PAG oil or similar would be a safer option as using water will create pitting in the cyl walls , ring lands or piston pin

 

Ummmm.....piston rings use a dynamic seal.....in other words, they need to be moving. They also rely on the cylinder pressure to push the ring against the bore.

I suspect your "water test" will yield disappointing results and rust in places you don't want.

The compression test uses the dynamics and cylinder pressure for the rings to perform their task.

The "water test" you describe uses a variant on the valve/head seal. I think Kerosene is used instead of water and the valves are in the closed position. This is only when the head is off the engine.

 

I’m not OP, but I know OP has stated he did do a pressure test. The results were a 75% leak down.

Yes, You read that correctly. 75% leaked OUT.

 

75% !?! good grief.....

Next step is the put about a teaspoon of oil in the cylinders, repeat the test. If the pressure rises, then the problem is rings

 

That was a water test too. He put water on the heads and 75% leaked out. He didn't do a pressure test.

Water isn't the way to test your seals for the aforementioned reasons and there aren't any standards (how much is ok and how much is bad).

 

I’ve done the heads with brake fluid but on the combustion cylinder side. Leave it sitting then later look to see if any leaked through the valves.

 

This is a good plan. Test dry, then wet. I use a oil can to squirt the exact same amount in each cylinder.

 

Nope. OP did do traditional air leak down test.

 

Dumb ass question deserves no reply I’m out

 

No, it was a test using air, and a cylinder leakdown test tool

 

I am trying to test without valves so that I can exactly pinpoint if the problem is in the ring (not "rings" only one leaking). I am doing a separate test for the valves.

When I test using cylinder leakdown or compression, the head must be on and if the test is negative, it could be one or more of the four things:

1. intake valves
2. exhaust valves
3. Piston rings
4. Head gasket

So I am looking for a way to test each one of those independently. If the first 3 are ruled out and I still have a leak, then it must be 4. But I really don't think it's it.

 

If you have air coming back out of the intake, you either have a valve leak, or you dont have it in the correct position.

 

No, I definitely have it in the right position. I tried 5 times. I have a rod with a marker plus the cams are tilted to each other, also I can slide a feeler gauge between the cams and lifters.

I know that it's coming through the intake but I want to test other possibilities. Like just because you have covid doesn't mean that you also don't have HIV... LOL

 

You can get a piece of 1/2-3/4" acrylic and cut it to cover one cylinder. Drill it to match the head bolt holes and drill/tap a hole to be about 1/4" below the top of the cylinder to be able to thread the leak down adapter to the acrylic. Thoroughly clean the deck and get an o-ring that will fit around the bore to seal it.
This will make a single bore leak down adapter which will remove anything other than rings or cracked piston from the equation.

 

I was thinking something along those lines but I really don't think it will seal it, unless I caulked the mating surface and then put 500 lbs on top. The pressure from the compressor would blow it right off

 

Hell, you already pulled one cylinder head at this point, might as well go ahead and lap in the valves and replace the valve stems seals while it’s off. If you do that, then might as well do the other too. Then while they’re both off pull the pan pop out the pistons and hone the cylinders and put all new rings.

 

I'm not doing that because i would have to remove the front differential. I really don't think the rings are a problem, just being a devils advocate

As for lapping all the valves, I think lapping (done it once before) is a hell of a delicate job and would rather not touch the ones I know seal fine. Because I think I can make it worse