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Discussion Starter · #1 ·
Hi everyone, I recently did a compression test on my 97 zj with the 5.2 v8 since I noticed oil all over my spark plugs. It was my first time and am getting mixed advice on what my problems are and was hoping you could give me input. My readings were:

1) 115psi 2) 155psi
3) 130psi 4) 125psi
5) 155psi 6) 155psi
7) 155psi 8) 155psi

afterwards I put a little oil in cylinders 1, 3, and 4 and tested again but cylinder 1 jumped up to 140 and 3&4 jumped up to 155. From my understanding it would be piston/piston rings but others tell me it could be a head gasket and/or valve seals. What do you guys think?
 

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its not likely valve seals - the valvres are closed during test.
Adding oil suggests a ring issue - BUT not necessarily worn rings.

Ideally a compression leak down test is next test, basically shop air is fed into cylinder thru plug hole and
you determine where the air is escaping. Into the oil pan, the intake manifold, the exhaust manifold or an adjacent cylinder.

How do plugs look at suspect cylinder? That may offer a clue.
 
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Leak down test is a good idea and pretty cheap. A lot of compression testers have a quick connect so you can just plug it into your compressed air line.

That said, there's about a 80% chance it's rings.
 

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Discussion Starter · #5 ·
I can do a leak down test but if it is the rings I’ve been told to do a rebuild. I’ve never gotten this deep in an engine so what type of rebuild would I be looking at? I think I’ll take it to the shop when I figure out what’s wrong but I’d like to be able to say exactly what it needs.
 

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A proper rebuild involves complete removal, disassembly, and repair/replacement of worn components with machining of the block, etc.

If it is the piston rings, the next step is at minimum removing the heads and inspecting the cylinder bores for damage. If the cylinder walls aren't badly damaged you may be able to get away with honing them and installing new rings. If they are heavily damaged (scored, which is deep scrapes) you will need to have the block bored and install oversized pistons to match the new bore size.
 

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I mentioned not necessarily worn - I wanted to to make clear that a leak past rings does NOT mean you MUST
disassemble and replace rings....

The question about plug condition was to see if your overfueling and washing down cylinder walls.
Also the rings could be stuck in piston groove causing a poor seal.

Both those we can work and NOT disassemble engine.
Maybe tell WHY you did a comoression test?
How is your jeep running? Any codes?

Sorry I'm a hopeless optimist. Think positive.
 

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Love your optimism jtec.

Even if the rings are worn a bit, you don't HAVE to rebuild it. An engine with those compression numbers could run another 5-10 years. It would just idle a bit rough, have more blow by, and be down on power/use more fuel. Probably kill catalyst a bit faster and need more plug changes too.

For all the snake oil they sell at auto parts stores, I've never seen anyone fix poor ring seal without disassembling the engine.

There are some scenarios where you can have poor ring seal and the bores not be excessively worn. In those cases you can do a quick light hone to reestablish the cross hatch and drop in a new set of rings once you clean the ring grooves. Good idea to check the main and rod bearings for wear (replace) or any damage to the crank journals (rebuild).

Worst case is you'll need the block bored and honed as yjsaabman said. At that point it's really time to just truck the whole thing down to your local machinist and have them rebuild it. Or buy a good used motor, or a crate motor.

You can buy a cheap bore scope on Amazon for like $20 that can fit in the spark plug hole and let you look at the cylinder walls. At least worth a look. Easiest thing to do if you are serious about figuring it out is to pull a head and take a look. You can get a decent snap gauge set and 4-inch micrometer for under $100. You don't need Starrett or Mitutoyo for this.
 

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Positive thinking - this is a 318 mopar old world cast iron will run forever. I called mine jason that SOB would NOT quit. .
Poor ring seal - the scenarios I mentioned Stuck rings, not uncommon, cylinder wash down very common and often ignored.
I totally agreee with those #s Deffinatly nothing to cause a panic.
 

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Discussion Starter · #11 ·
I mentioned not necessarily worn - I wanted to to make clear that a leak past rings does NOT mean you MUST
disassemble and replace rings....

The question about plug condition was to see if your overfueling and washing down cylinder walls.
Also the rings could be stuck in piston groove causing a poor seal.

Both those we can work and NOT disassemble engine.
Maybe tell WHY you did a comoression test?
How is your jeep running? Any codes?

Sorry I'm a hopeless optimist. Think positive.
I did the compression test because my check engine light was due to cylinder 1 misfire. I decided to change the plugs and noticed most were covered in oil. I changed the leaking valve cover gasket hoping it would fix it but no luck. My new plugs look good, not burning rich or lean.
 

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Discussion Starter · #12 ·
Love your optimism jtec.

Even if the rings are worn a bit, you don't HAVE to rebuild it. An engine with those compression numbers could run another 5-10 years. It would just idle a bit rough, have more blow by, and be down on power/use more fuel. Probably kill catalyst a bit faster and need more plug changes too.

For all the snake oil they sell at auto parts stores, I've never seen anyone fix poor ring seal without disassembling the engine.

There are some scenarios where you can have poor ring seal and the bores not be excessively worn. In those cases you can do a quick light hone to reestablish the cross hatch and drop in a new set of rings once you clean the ring grooves. Good idea to check the main and rod bearings for wear (replace) or any damage to the crank journals (rebuild).

Worst case is you'll need the block bored and honed as yjsaabman said. At that point it's really time to just truck the whole thing down to your local machinist and have them rebuild it. Or buy a good used motor, or a crate motor.

You can buy a cheap bore scope on Amazon for like $20 that can fit in the spark plug hole and let you look at the cylinder walls. At least worth a look. Easiest thing to do if you are serious about figuring it out is to pull a head and take a look. You can get a decent snap gauge set and 4-inch micrometer for under $100. You don't need Starrett or Mitutoyo for this.
I’ll call around and see if I can get some quotes on a rebuild. Hopefully it won’t cost an arm and a leg!
 

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Discussion Starter · #13 ·
Positive thinking - this is a 318 mopar old world cast iron will run forever. I called mine jason that SOB would NOT quit. .
Poor ring seal - the scenarios I mentioned Stuck rings, not uncommon, cylinder wash down very common and often ignored.
I totally agreee with those #s Deffinatly nothing to cause a panic.
Man, I hope it’s not gonna cause too much of a pain. I bought this jeep for my son before he turns 16 but it’s being way more of a hassle than what I thought it’d be. Guy who sold it to me screwed me, I’ve even had to get the tranny rebuilt, I test drove it and it ran good the next day it wouldn’t go into gear and kept slipping cuz the clutch was burnt.
 

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no you are fine - my poor communication skill.
The compression readings are OK - not perfect, not critical, I was being optimistic there are some other things we can look into but NOT a new set of rings......

Why did you do a compression test?
A 1997 has a good diagnostic system - are there any codes?
Any issues or problems?
 

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Discussion Starter · #16 ·
no you are fine - my poor communication skill.
The compression readings are OK - not perfect, not critical, I was being optimistic there are some other things we can look into but NOT a new set of rings......

Why did you do a compression test?
A 1997 has a good diagnostic system - are there any codes?
Any issues or problems?
It was throwing codes about a misfire in cylinder 1 so I replaced the plugs and the old ones had oil all over them so I did the compression test.
 

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All 8 plugs had oil ?
Tey were Black - WET or DRY?

I'm hoping to hear Black and dry, what would be carbon fouled... I'm Always positive....
 

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I won't give up - there is a plan B - something to try.... "I ain't dead yet"
 
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I’m not sure how many miles are on it, I don’t think it’s the original engine. I didn’t notice which is my fault but when I bought it the title said 160k and the odometer said 150k.
If you rebuild, the stock heads are prone to cracks and new heads are expensive. Have them checked first before you do anything else.

I tried a crate motor once, local rebuild once, another I did myself short of some machining. Not much luck and the warranty on engine rebuilding is a quagmire and an onus. Then I spotted a used 5.9 motor with 98k miles from a wrecked niner and it's still running great over 100k miles later. That was $800 plus all the extra stuff like seals, gaskets, tax etc. The crane and stand cost an extra $200 back then. So you could look for a decent used motor while you drive the current one into the ground. Just an option.

But hopefully Jtec can perform a miracle for you and it's not too bad.
 
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