No compression---where to start

[gregstukey]

And before pulling the head, is removing the rocker assem. and tapping with a tapper on the valve a good idea? I was thinking that im not going to get a proper leakage test if the valve is stuck (which all tests are pointing the finger to) right? -G God i love this van.

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[lilredex]

Originally Posted by kev2

some thoughts:

did you do a "wet" and "dry" reading? simple just add some oil into cyl..will help ID if a ring issue...

also a cylinder leak down test... shop air is attached to gauge flex hose .... applying pressure you can get a good idea where pressure is leaking....ie hissing air out throttle would suggest valves, oil fill cap sound would have you look a piston sealing.....

You need to do as previously suggested, the wet test changed nothing so it looks like the valves. Pressurize the cyl. with air. Got the valve cover off? You can see when the valves are closed (or supposed to be). Crank it over and you'll see the rocker arms push down against the valve springs- valve open. They open at different times but both (intake and exh.) are closed on the compression stroke, there is a pause while they are both closed, and this is where you do the test. Don't take off that head until you pinpoint where the problem is!!!

[gregstukey]

Did the wet test and no change in value. Still reading 0. So now Ill add some air pressure...and listen. Thanks, Ill report back when I do the leakdown.

-G

[dhvaughan]

your compressions look pretty good, other than the one blowed out cyl.
based on the fact that it runs, and doesn't knock, that's all good.

there are 3 possible problems. the most likely is the common problem of a cracked head in the 5.2/5.9 magnum engines. this will be the most expensive, as it will require head replacement.

burned valve, broken rocker, bent/worn push rod. maybe. unlikely.

head gasket. this is unlikely, since you don't have water in oil or overheating.

a couple more things to do before you pull the head. pull fuel pump fuse or something so it won't crank, and while an assistant spins the starter, observe the valves on #4 and see if the push rods are moving properly. if not, remove rocker and replace push rods. observe that valves are moving up and down. if so - then you've done all you can do, and its time to pull the head.

you mentioned black plugs, so while you are doing this, go over to 2nd gen ram and do a search on plenum, and you'll find another common problem that you can address when you pull the top end off.


just preparing for the worst. a burned valve can be rebuilt by your local machine shop. if the head is cracked, i would not weld/repair it, but replace it.

here's a cheap rebuilt OEM head. same weak casting, but ok.
http://cgi.ebay.com/ebaymotors/DODGE...Q5fAccessories

new/better casting.
can't find one on ebay. used to be common. still looking.

[gregstukey]

Thanks so much. This has been one of the most helpful forums I've visited. Thanks for taking the time and giving solid advice. A few more tests and I'll let you know what happens.

-G

[gregstukey]

Push rods seem ok and functioning and so do rockers ( pulled them today and inspected). Still reading 0. Will do leak down tomorrow--need to get it to shop air. But i think im down to pulling the head. This is going to be fun.

-G

[gregstukey]

Did the leakdown and I can hear the most air from the exhaust ( someone stole the cat so the "new tailpipe location" is just below the manifold--that is where the most air could be heard from. Nothing at throttle body and nothing at oil cap...

Does that mean exhaust valve? (did the test with rocker arms off to ensure a sealed cylinder).

[Mobile Auto Repair]

Yes the leak is the exhaust valve. At least you now have found the problem. Time to take the head off and have it reworked.

[carpetvan]

you might want to remove the other head also, they both went down the same road. use fel pro gaskets "do it once, do it right" "fel pro" "where sealing is a science" also i recommend blue stripe valve cover gaskets, they may or may not come with the head set. toss those rubber gaskets

[gregstukey]

Nice. I was pricing gaskets out this morning and was wondering which to get. Thanks for everyone's help in the diagnostic. I'' let you know what I find.

10-4 on the other head. Gonna pull that one too.

-G