Is it rings or Head gasket, Compresion test results

[Ted 87 XJ Pioneer]

I did the test here's my readings

1=135 psi
2=105 psi
3=137 psi
4=110 psi
5=142 psi
6=130 psi

I did the test because i seen the exaust was smoking a little, I put a plain peice of paper up against the tailpipe to see if there was any oil coming out.... and there was none, so I don't know if this a problem or not on # 2 and 4 being so low.

Any advice before I buy a new engine? and if I need a new engine, where can I get a good deal/price?

tia

[RTicUL8]

http://www.rebuilt-jeep-engines.com/jeep-amc-engines.html

[Ted 87 XJ Pioneer]

So does it need rebuilt?

[RTicUL8]

I'm at work right now, and I don't remember the allowable range. I have an '88 FSM which I'll check when I get home.

[rixXJphx]

Those are raw compression test readings, and they indicate bad rings.

You could do a a leak-down test also, but I think you'll get similar results.

If this is the original engine from '87, you prolly have about 225k miles, so these readings are just about what would be expected.

I don't know about engine sources, other than to say 'Run Away!' from the cheapo long blocks at Checker/AZ/PB.

Good luck.
-Rick

[Ted 87 XJ Pioneer]

the range is 120 to 150 psi w/ 30psi varince

[FatXJ]

Have you tried Sea-Foam or GM Top Engine cleaner? A lot of time gunk will build up on the valves which will not allow them to close properly and you will get a small air leak.

It's cheap and it's worth a try.

You could also try the engine restore stuff unless you really wanna fork over $1200+ for a new motor.

[5-90]

If the low results are in individual cylinders, it is usually indicative of either -
1) Worn rings
2) Compression leakage into cooling jacket (fairly rare, fortunately)
3) Crudded valves resulting in slight compression loss.
4) Crack in or near valve seat, usually exhaust.

If the low results are in adjacent cylinders, the cause is almost always a head gasket which has eroded in between two cylinders.

Either one is a fairly "major" job (you will have to remove the head either way!) You can narrow things down further by doing a "wet" compression test - pour about a half tablespoon of oil down the plug hole, turn the engine by hand 3-4 revolutions, and recheck. If the low readings come up to par with the rest, you have a re-ring on your hands. If not, it will likely be a top end job.

Does this help at all? Feel free to email as well, if you want more detailed help...

5-90

[Ted 87 XJ Pioneer]

Thanks 5-90 and fat-xj I will try these tomorrow! I really don't want fork over 1200 yet............ YET hehe

[Eagle]

Ted, I would run the compression test again.

Let it sit overnight, then unplug the fuel pump relay and run the test before starting the engine. The cylinder walls will then be fairly dry. Record the results. Then run it again, but give a few squirts of 10W30 or 10W40 motor oil into each cylinder before test. Record those results.

Compare the results. If the oil caused a significant (whatever that is) increase in compression, your problem is rings. If the oil does not significantly increase the compression, your problem is more likely to be valves.

[Ted 87 XJ Pioneer]

Thank-you Will do. BTW I couldn't find that sea foam anywhere today!

[ILLXJ]

NAPA carries it.

[Ted 87 XJ Pioneer]

thanks