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Old 04-13-2012, 09:32 PM   #1
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oil blow by?

Okay, I have been pouring over these old threads to avoid asking repeat question/concern.
I have 89 YJ with 4.2 5 speed. I bought it with rear main seal leaking. No problem, fixed and moved on. However, I am getting a lot of oil in breather unit. I had mechanic check it out and he changed PCV and CCV put on new hoses and things went well for anout three weeks. Then I noticed loss of power and a lot of smoke in valve cover and coming into air breather from CCV. A lot of smoke. Press accelerator and puff of smoke. short press, short puff. Long press of accelerator, long puff of smoke. Not what I wanted to see. I am preparing to change rings this weekend since all crankcase ventilation has basically been replaced but wanted to talk to other Jeepers to get last ditch opinions. Thanks for any and all replies.

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Old 04-14-2012, 08:49 AM   #2
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I dont see rings helping you. Unless you take block to be bored and over size pistons used. Might as well do it right, even if you got to find another block to take to machine shop, so you not down waiting on it to come back. I got a buddy that when i bring one in he gets it on the machine 1st thing. Mostly cause I got it torn down to bare block with EVERYthing removed and I have it pressure wash so zero oil on it.
I have only pulled down about a million engines, but when the rings are letting that much burnt oil get into the crank case, the bores are way out of spec. Now I have see it once where the rings gave up before the cylinder bore but that was on a Toyota 22re.
So you got to get the bores back into spec. A good machine shop will check every bore and bore out to the largest one to the next step in piston size. I like to pull down the head also and clean up the valves and the combustion chamber of all that carbon. If your valve guides are in good shape, get all new seals and have the heads checked and reseal the valve guides.

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Old 04-14-2012, 08:54 AM   #3
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I agree, sounds to me like you're looking at a full engine overhaul. You can throw rings at it, but that will be a short and temporary band-aid before the rings will fail again, likely with catastrophic results the next time around. Should be pretty evident if it needs a bore with new pistons and rings just by looking at the cylinder wall. If scratches are noticeable then they're done for, you can run your fingernail along as well. If you can feel them, time for a bore. Shouldn't be terribly bad to have the engine rebuilt though, maybe $1200 or so from an independent shop.
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Old 04-14-2012, 09:04 AM   #4
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12 bucks a hole to machine. The machinist will want to get pistons for you since he will want to bore to those instead of some random number. After that just buy rings to fit the over bore. Since you not having oiling issues check all bearings and see if they ok. If not replace as a set. The size should be on the underside so just replace with the same. head tear down can be down at home with rental tools from Autozone or similar.
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Old 04-14-2012, 01:24 PM   #5
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Any chance to be over reacting and problem still be tied to blocked CCV? I have no problem rebuilding but don't want to do for nothing and still have problem. Mileage was not that high....140k I assume since speedo has been replaced. Seen lot of engines go longer but I guess u never know. Lot of smoke in valve cover regardless. Thanks for all replies and information.
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Old 04-14-2012, 10:22 PM   #6
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no, these engines are notorious for blow by. need to do a rebuild. most likely it has gone through long periods of time sitting then being drivin a lot. between owners and what not. thats not good on an engine
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Old 04-15-2012, 04:34 AM   #7
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Hard life, long times between oil changes, or a combo of both will have more effect than mileage. Blow by is rings. Rings have lost the ability to maintain a seal in the bore. Even if you just ried to replace the rings only, you would have to deglaze the cylinder walls. Doing that will open the bore even farther, if you dont the rings will never seat.
I gave you the cheapest way to get this done and have a good short block in the end.
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Old 04-16-2012, 06:55 PM   #8
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Thanks again for all the advice. Took all aparrt over weekend and found my problems. 2 broken rings and one completely missing. Also replacing a piston. Dreaded startng job but will put back together right. Seriously question PO and his maechanic. Only head bolts seemed torqued, everything else just came right on out, including exhaust manifold bolts. I have spare ride and time so I will get it back together right this time.
Seriously, thanks again to all of you that responded.
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Old 04-16-2012, 07:55 PM   #9
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Sorry for the bad news, but then you will know what you got to run with!

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