cpunix

A guy sold me 150K mileage engine (pulled from '90 cherokee 4.0L) for a hundred bucks. Said it have one cylinder loses compression. I'm newibe on rebuilding.

Give me tips, direct me a threat form or something that get me going to fix this thing.

Thanks in advanced.

xj wheeler

A cylinder low on compression could be several things.

Head gasket leak/cracked head
Broken/bent valve
Worn valve seals
Damaged rings
Damaged cylinder or piston
maybe more

Basically you need to start checking things off to find the problem.

fishtaconc

^^ This... With out knowing what the compression actually is, or anything else, its gonna be difficult to offer any advice to a simple solution.

DFlintstone

I did a bit of searching for "wet" compression test. Didn't find anything outstanding. Pulling the fuel pump relay, grounding the coil wire, and keeping it at wide open throttle where mentioned. I usually go about 7 strokes. 5 should do it, but 2 more is cheap insurance!
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6. If all the readings are within specifications, there is no need to do the wet test but if there is variation between cylinders, then squirt about a tablespoon of lubricating oil into each cylinder and repeat the test. If the pressures increase appreciably and come up to the manufacturer's specifications, then you can be sure there is piston ring and/or cylinder and piston wear.

7. If after adding the oil, the pressure does not go up, your valves may not be seating properly. Or there is a issue with the head gasket.

cruiser54

Unfortunately it's hard to do a compresson test on an engine out of the vehicle......

akita8

Pull the spark plugs and see what they look like. Remember which hole you pulled them from.

kps

do you have access to a leakdown tester? you can listen to where air escapes, & tell quite a bit about general shape. you just have to be able to turn engine over with a wrench to get each piston at top dead center. checking one at a time.

DFlintstone

^//^ Good idea Kps. THAT was helpful. Or, if your sure there is a problem, pull the head and have it checked out. (or you can pour kerosene or = into the ports and watch around the valve seats for leaking)

cpunix

Hello again,

thanks for the inputs. I looked inside and didn't see any damage such as rod, crack mark, something like that but ain't sure about the ring. There's dirty stuff with water inside. Any idea how to clean it out? Any suggestion?

Here's the pictures;

cpunix

My friend may have one. Will keep you posted in here.

Thanks! (along with everyone!)