The real question becomes: Where is the pressure going? Around the rings, or out the valves??

I think a leakdown test is in order.

 

You are having some of the same experiences I had. It was not a fun job. It was during covid lockdown, so I spent a LOT of time in the garage. I know my thread was long and you may have missed this.....

Post #16 from my thread.
"I'm down to the last cylinder (#1) for the spring and seal replacements. It's been slow going as I'm doing a bit each evening after work. I have a loud *** Harbor Freight air compressor and I don't go past 7:30 running it. Furthermore, I had my tools slip while a spring was compressed a few days ago and everything went flying, never to be found. Had to wait on new spring retainer hat and keepers from the dealer.

I have a question though. I'm on the driver's side bank, which is cylinders 1,3, 5 and 7. I'm using air going into the spark plug holes to keep the cylinders pressurized, so the valves stay up. When I air up each cylinder on this bank, I'm losing loads of air coming out the throttle body. It's flowing out so fast that I have to hurry and get the spring compressed and the keepers back on before the valves fall. The compressor will drop to zero while running eventually. So far 3, 5 and 7 have exhibited it, so I'm sure 1 will do it too. This was not the case with the other bank, as they held the pressure. The fuel rail and injectors are removed, if it matters. Any idea why I'm losing all this air? The truck drove fine, with what feels like loads of compression.

Post #26

Originally Posted by Dodgevity
I'm hoping that the manual manipulation of the valves, springs and seals may have things out of line right now and when I put it back together and start it, hopefully everything will vibrate back into line.
Quoting myself here. My suspicions have been bolstered and likely confirmed.

Today, I aired up a cylinder, placed a block of wood of top the intake valve spring and tapped it with a steel hammer. The change was not what I was expecting, but it confirmed my initial suspicion. When I tapped it, air began gushing right past the valve itself. I removed the spring and hooked it back up again and it sealed. So that's telling me that there is a small bit of play in the valves that can cause them to not be perfectly aligned when manipulated. It could be that the spring is off center or whatever, after manually compressing it. So I believe I just need to run the motor and hopefully things will vibrate into place.
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My advice to you is, stop worrying about why you're losing so much air and forge ahead. The biggest worry with running out of air is the valve falling into the cylinder. That would be a nightmare. The rope trick didn't work for me, I had to use air. Luckily I figured out a sure fire way to prevent the valves from falling in... apologies for calling it TDC. TDC is really a combination of things. I should have called it something like....the apex of the cylinder's ascent.

Post #15

Originally Posted by Dodgevity
Anyone know if when the 4.7L pistons are at TDC and say (God forbid) valves fell in, would part of the valve stem still be sticking out, or would they fall completely into the cylinder and disappear?
I'm going to answer my own question here. When the 4.7 piston is at TDC, the valves will not fall into the cylinder. They will drop roughly an inch or less, then hit the piston with plenty of stem still protruding. I guess I should have known, since this is an interference engine, so the piston can touch the valves if things were out of time. To find TDC on each cylinder, I stuck a long screwdriver through the spark plug hole so it was sitting on the piston. I then rotated the engine, watching the screwdriver rise to max level, stopping just before it started the descent.

 

My theory on air pressure loss is that the application for an engine leak down tester is to perform engine leak down tests on a "warm" engine at near operating thermal expansion in timely succession. Our application of servicing valvetrain, over time, on a cool engine is not the correct application for this tool. I suspect the air is blowing by the piston rings, again because the engine has had a chance to cool down and clearances are wider. Maybe it applies to valves as well? Don't know? I'm just speculating at this point. Perhaps the professionals have a better way of doing this?

 

How much leakdown are you getting? Even on a cold motor, you should be able to build enough pressure to hold the valves shut. I regularly did valve seals on cold engines, and didn't have that problem.

 

It's something about the 4.7 that causes this phenomenon. In my case, the air was rushing out of the throttle body so fast, the compressor was running full tilt. When I tapped the top of one valve with a hammer, it sealed and air pressure was able to rise in that cylinder. I was never able to explain it. I knew the engine was good, so i had to move forward on faith. That first start was scary though. To say it ran like complete sh*t for a min or two is an understatement. It was shivering, coughing and wheezing. I thought all was lost, then it smoothed out. Dismay followe by a big smile. It drives great today

 

Today I removed the driver side valve cover for the first time. It had heavy oil deposits on it. Guess I forgot that I must have hand cleaned the passenger side valve cover before putting it back on two years ago and all my flushing and cleaning hasn't been that miraculous after all. Darn it!

 

Keep i mind all of us "olde phartes" has done similar things over the years. That's why we know to look for things because they have bitten us on the posterior before. If you've never made a mistake, you've never made a discovery. I've made many discoveries in my life. I've even got the scars to prove it.

 

Good Judgement comes from experience. Experience is usually the result of bad judgement.

 

I didn't want to say it, but when I looked at the before and after pics, I thought to myself, that looks a bit too clean....like hand cleaned. But momma always said if you got nothing good to say, keep your trap shut!

 

Thanks. This project is completely transparent. What I see. You see...

Dodgevity, seems like I saw one of your posts where you talked about using colder spark plugs. Did I see that right? I've seen some Mopar guys favor colder plugs. Have you tried colder plugs? What did you notice from them? Thanks