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post #1 of (permalink) Old 12-29-2000, 02:55 PM
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Compression test results

Here are the results or my compression test, both wet and dry and the condition of the spark plugs.
1 2 3 4 5 6
w. 155 150 150 160 150 150

d. 155 155 155 166 155 155

p. norm norm norm ** norm norm

** - brown deposits on insulator and green crust on tip of firing end.
I think I found where the crack is in my head (#4). Also noticing an lot of steam in the exhaust. According to my Haynes manual, my compression should be beween 120 - 150. Is the wet test increase of 5lbs enough to show bad rings or can I just swap heads and enjoy my Jeep for another year before needing to worry? Very limited budget but I need to do what it takes to keep it on the road. All input very useful. Thanx Graeme.

'88 Sahara
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post #2 of (permalink) Old 12-29-2000, 05:04 PM
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Re: Compression test results

that difference... is minimal.. you will be alright.. there is a certain percent.. but i dont know it off hand.. when you want to worry.. is when its like 120-125.. and it jumps up to 150.. then your rings are pretty shot..

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post #3 of (permalink) Old 12-29-2000, 06:30 PM
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Re: Compression test results

i agree w/ jeepgod- my cylinders all run around 150 also w/ little deviation. your readings look ok to me. if it's running good i wouldn't do a thing![img]/wwwthreads_images/icons/smile.gif[/img] if that one plug is fouling-replace it as needed.

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post #4 of (permalink) Old 12-30-2000, 12:58 AM
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Re: Compression test results

Thanx for the replys. Glad I only need to worry about the head. Looks like that 4.0 head swap is coming sooner than I thought. I have another question though. If the rings are good, why was the blow-by hose dumping oil into my air cleaner? What else causes this so I can fix while ripping apart the engine anyhow?

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post #5 of (permalink) Old 12-30-2000, 07:02 AM
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Re: Compression test results

could be the pcv valve.. what happens when the rings go bad.. is vapors and whatnot from the combustion chamber pass by the rings and pressurize the bottom of the engine.. once it is pressurized.. then the oil from the top of the engine.. ie. top of head... can not drain down into it.. since its of a higher pressure so the oil takes the path of least resistance and goes out the hole in the valve cover and into your air filter..

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post #6 of (permalink) Old 12-30-2000, 12:29 PM
 
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Re: Compression test results

I only have three words for you....
LEAK DOWN TEST.
Do a leak down test to tell if anything is getting out of the chamber, and where it's going....
-----------------------------

Your head is not cracked unless you are getting WATER DISAPPEARING from the radiator, or water in the oil.
The easiest way to check for even traces of antifreeze in the oil is with a freon sniffer.
Modern antifreeze contains halogens, and the sniffer will find them, just sniff the dipstick tube.

If you are loosing water, but it's not showing up in the oil, then do a block pressure test.
If you are still loosing pressure, you may try one of the fancy dye tracers to find the leak, or you may take the head off, use a block off plate, and pressure test again.
That will rule out the engine block it's self, and leave you with just the head.

Use a magniflux around the valve seats, (especially in between the seats) to look for the leak....
It' may be just a seeping plug, or leaking head gasket, so don't just assume it's a cracked head.
Look the head gasket over carefully for signs of a leak, or water tracking.

The crap in the combustion chamber may be just crap from a worn valve guide, or bad valve guide seal.
If it's guides, you will have to remove the head to fix, but it's not real expensive.

If it's a leaking valve guide seal, they can be fixed with out removing the head....

So good diagnosis is a must for your problem...
Try not to jump the gun too much, it may be a little bit of nothing (and often is).


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