mycherokee1989

Pulled block out for second time (first in Dec.) to rebuild again, because we were having blowby in the crank, and oil blowing through top of valve cover. Took block into machine shop, and they said that cylinders did not need to be bored out, and that we should not be having this problem, and what must be happening, is that there was not a good seal in between the piston, and the cylinder. (broken rings, or worn cylinders could cause this) But when we pulled block apart, no broken rings, and machine shop says that cylinders are not too worn, and gap on rings was fine.
The theory is that detenation is happening, where the cylinder is firing at the too early, and somehow, the pressure is making it past the pistons and the rings, causing pressure in other areas such as valve cover.
Ideas: Computer problem the machine shop said??
Engine knock (I haven't noticed, but we just realized knock sensor was not torqued down to 89ftlbs like it should have been causin it to not work correctley?)
Engine just needs to be bored and oversized pistons.

So plans to do now are bore cylinders, oversize pistons, and put it back together. This is a continuation of the Darn you xj thread for those of you that read. https://www.cherokeeforum.com/f2/darn-you-xj-14190/
Please only help on this thread, I got a lot of unnecessary crap on the last one that made me dissapointed in this forum. We are going by our Haynes manual for this year cherokee btw.

diskman

Hmm.. Double check and re-check your piston ring end gaps when installed at top, middle and bottom in the bore. Also, try to be present when they are being assembled so YOU can verify the order and alignment of the rings as they are being slid into the bores.

With a fresh & complete re-bore of the block and new pistons and rings, you should be set.

Double check all your rod and main bearings for *ANY* damage/contamination and replace if needed. Double check all the oil journals too. Sounds like this rebuild was jinxed from the start so you guys NEED to double check and tripple check EVERYTHING before you button her up again.

Otherwise, find a nice-running one and re-install that one.

mycherokee1989

The crank bearings had some very minor scratches on them, but It was not down to the copper on the bearings, and my step dad says unless we can see copper, we don't need to worry about it. True?
Probably replace just to be safe.

RCB

Your compression is good on all cylinders? Did you also have your head machined? x2 on your journals.

Out of curiosity, when you or whomever rebuilt the motor, the oil pump relief spring was a stock one right? Not a stronger spring and not shimmed? A stronger or shimmed spring are sometimes used by people to cure other ills when they can't figure out low oil pressure, so in a new motor, said oil pump can deliver more pressure than its supposed to.

motoxpete

Stop right there!!!!! There is nothing wrong with you motor..... 1987 threw 1990 were the worst for this problem.... i know because I have the same 1989 and going threw the same ****. I have to change my air filter on a weekly due to oil build up in there. The first couple lines of that link said it all......NO NEED TO REBUILD YOUR MOTOR!!!!



http://jeep.off-road.com/jeep/articl....jsp?id=257985

COSXJFAN

OK, I just read through all of these posts, as well as the previous thread. I need to know if you checked the piston ring grooves?? If your motor had 150,00+ miles on it, there is a good chance that the pistons are shot. If you replaced them, my apologies, I didn't see that stated in any of the posts. Have you done a comp test since the hone and reassembly?? If so, what are the numbers. I'm truly looking to help, unlike some of the folks that posted on your previous thread. FWIW, guys, ease up on the guy!! He is trying to do this himself, and use "our" forum to help him through it!! I can't imagine that any of you slid out of the womb with all of the mechanical knowledge known to man, give the guy a break!! 89, get back to me with the answers to the questions I asked, and I'll try to help any way I can. Laters!!

RCB

I am guessing (hoping?) that he had already went through all that (regarding the new vacuum lines and grommets) and actually diagnosed it as a high pressure situation.

But if you haven't, that's the first place to stop. I did that to my 87 years ago and cleared that particular problem up pretty fast.

COSXJFAN

He mentioned low compression in a previous post...I was thinking the same thing until I saw that.

RCB

If his rings check out and there is low compression that it would have to be his valves and/or valve seats. Could have a collapsed lifter if the head wasn't rebuilt.

COSXJFAN

Yep, the old process of elimination!!

mycherokee1989

head was rebuilt. Pistons were all fine, except 2 which we replaced b/c of broken rings. A big indicator of the new problem is that one of the replaced pistons when we pulled them out this last time was messed up in the groove. And that was a brand new piston that only had 1600 miles on it. (rings on the piston were fine.)
When we did the compression test we got 120 ish on two of the pistons which I believe was fine, and then below 80 on all the others -- not good.
We also did a leak down test, but could not isolate where the air was blowing by, but it showed it was leaking really bad.

MotoxPete, I know about the blowby problem in those year xjs, but mine was getting crazy, which is why we rebuilt the motor in december the first time. After the rebuild I was still getting blowby, but probably because rings were not seated, but nowhere as bad as before. When you would take the oil cap off the valve cover tho, there would be a lot of pressure in the engine, and kind of blow it off. That was causing oil not only to go to the air filter, but more to go through the grommets of the valve cover, which showed us there was way too much pressure.

Thanks for the help guys

mycherokee1989

head was rebuilt and we got new lifters. Would I be able to look at a lifter and tell if it was collapsed.

mike37

if you bore it and hone you will cure your problems
be sure to use the same type of rings as stock not harder ones

jinx

just out of curiosity what type of oil did you use for your break in? if everything was done correctly in first build but you used synthetic oil most likely your rings did not seat properly.

motoxpete

Yeah your problem sounds a little worse then mine lol..... hope everything comes out ok.