Quick question regarding using air to keep the valves closed.. - JeepForum.com
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post #1 of 25 Old 03-18-2020, 04:20 PM Thread Starter
LelandGray
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Quick question regarding using air to keep the valves closed..

Hey guys,

So I went to start changing out my valve stem seals, etc. I hooked up my air compressor to the first cylinder using an adapter I bought on Amazon that connects the air hose to the cylinder via the spark plug hole. I have my compressor set at 70 psi. I connect the air hose and I can hear/feel air coming out of the intake on that same cylinder. So basically, I'm getting air leaking through the intake valve..

Has anyone else done this? Did you experience the same thing?


2001 WJ Limited w/ QuadraDrive
Bilstein 5125's
jgcparts 2.5"/2" BB
JK take offs & 265/75R17's
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post #2 of 25 Old 03-18-2020, 04:30 PM Thread Starter
LelandGray
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I just tested a different cylinder (second back from the front on the drivers side), and it leaks just like the first one.. So is this air leaking past the valve a big deal? is it normal? I hope my big job didn't just turn into an even bigger job.

2001 WJ Limited w/ QuadraDrive
Bilstein 5125's
jgcparts 2.5"/2" BB
JK take offs & 265/75R17's
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post #3 of 25 Old 03-18-2020, 04:33 PM
2oldjeeps
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i never used air. i bring the piston up on that cylinder so i cant drop a valve.

dont think you could "loose"one anyway.
leaking valve is another issue...at least by trying air you found it...

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post #4 of 25 Old 03-18-2020, 04:57 PM Thread Starter
LelandGray
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I'm thinking about just doing it that way, with a rope just for extra safety. Now that I have everything torn down to where I'm at, I wonder how much more work it would be to just pull the heads. From what I can tell, I just need to remove the timing cover (which I was going to be doing anyway) and the exhaust manifolds. Can anyone else confirm that I should NOT be having any air come through the lower intake runners?

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post #5 of 25 Old 03-18-2020, 06:21 PM
scott_0
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are you certain the valves are closed on the cylinder you’re working on?


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post #6 of 25 Old 03-18-2020, 06:24 PM Thread Starter
LelandGray
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Quote:
Originally Posted by scott_0 View Post
are you certain the valves are closed on the cylinder you’re working on?
As far as I know they SHOULD be... The camshaft is out, so nothing would be pressing the valves open. Unless I'm missing something.

2001 WJ Limited w/ QuadraDrive
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post #7 of 25 Old 03-18-2020, 06:33 PM
wjkeith
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Quote:
Originally Posted by scott_0 View Post
are you certain the valves are closed on the cylinder you’re working on?


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This. The cylinder you’re working on needs to have the valves closed.
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post #8 of 25 Old 03-18-2020, 06:36 PM Thread Starter
LelandGray
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Quote:
Originally Posted by wjkeith View Post
This. The cylinder you’re working on needs to have the valves closed.
But if the camshaft has already been removed, and nothing is pressing down on the valves to open them, wouldn't they be closed by default?

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post #9 of 25 Old 03-18-2020, 07:26 PM
CarlJH
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so you've removed the cam shafts? then definitely there shouldn't be any air escaping from the cylinder when you apply the air to it.
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post #10 of 25 Old 03-18-2020, 07:37 PM Thread Starter
LelandGray
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Quote:
Originally Posted by CarlJH View Post
so you've removed the cam shafts? then definitely there shouldn't be any air escaping from the cylinder when you apply the air to it.
I was afraid of that... So, bad valve seat then? That's the only thing I can think of. I didn't really want to spend more money on this 🙁

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post #11 of 25 Old 03-18-2020, 07:56 PM
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Originally Posted by LelandGray View Post
I was afraid of that... So, bad valve seat then? That's the only thing I can think of. I didn't really want to spend more money on this ��
Yes, it seems as if the valves aren’t making a good seal. Maybe give the valve stem a very light tap. It may be hung up.
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post #12 of 25 Old 03-18-2020, 08:05 PM
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How many miles on this engine?

I had one of these 4.7's open one time for a leaking head gasket. It ran just fine, but was overheating. When i got the heads off, i sent them in to be resurfaced, then took them apart myself and lapped the valves and replaced the valve guide seals. I was surprised how much lapping they took to get a good seal on the valve seats. I dont think i needed to do the valves to get it to run well, but im sure it helped to bring the compression up some when i was done. What I'm getting at is.....if you still have decent compression in all the cylinders, i dont think i would get crazy about a little air leaking by the valves. Obviously, we wished they didnt leak a little, but its not the end of the world? Depends on how long you plan on keeping this machine....

You ARE about half way there already to popping the heads off. Just need to undo the exhaust manifolds and the intake, PS pump, Alternator, AC pump, and timing cover. But in reality, you need to take the front of the engine off anyways to get the timing chain slack adjusters reset....

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post #13 of 25 Old 03-18-2020, 08:15 PM Thread Starter
LelandGray
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Quote:
Originally Posted by Bigrigr View Post
How many miles on this engine?
About 205k

Quote:
What I'm getting at is.....if you still have decent compression in all the cylinders, i dont think i would get crazy about a little air leaking by the valves. Obviously, we wished they didnt leak a little, but its not the end of the world? Depends on how long you plan on keeping this machine....
That's what I was thinking, too. Ideally, I'd like to keep it another 6 years (my son turns 16 in 6 years)..

Quote:
You ARE about half way there already to popping the heads off. Just need to undo the exhaust manifolds and the intake, PS pump, Alternator, AC pump, and timing cover. But in reality, you need to take the front of the engine off anyways to get the timing chain slack adjusters reset....
Well, I've already pulled all the AC lines, the alternator, the front end, radiator, etc. I'm about to pull the timing cover so I can replace the timing chains and guides. How much more work to pull the heads? I'm just afraid of what I'll find and then I'll HAVE to fix it.

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post #14 of 25 Old 03-18-2020, 08:47 PM
CarlJH
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if its that far apart then I'd take the heads off as well, there only held on with what, 12 bolts each side, and you can get the valve seats pinned so you wont have to worry about them come out.
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post #15 of 25 Old 03-19-2020, 12:10 AM
Bigrigr
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Thats alot of miles, not at all unreasonable to have a little compression loss past those valve seats. If you have gone this far, and plan on keeping this Jeep to pass on to the kids, i would say you will will probably kick yourself for not taking the heads in and having them rebuilt. They really arent to scary to get off, you have already set into motion the more nerve racking parts(timing chains and tensioners). Sure there is more exspense, and a little more time, but you will be glad you did when you are done. That's my 2 cents....

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