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Unread 11-22-2007, 07:58 PM   #1
rezalien
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1995 YJ Wrangler 
 
Join Date: Aug 2006
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replacing rod bearings...advice?

Looks like I'll be replacing the connecting rod bearings pretty soon in my 4.0...the knocking coming from the bottom/rear of the block is bothering the H*LL out of me! (it's not Torque Converter bolts, fairly certain it's connecting rod bearings)

1. Should I replace the rear main seal while I'm down there?
2. Because I'm just going to drop the oil pan, how difficult is it going to be to actually replace the bearings?
3. Should I drain the oil BEFORE dropping the oil pan?....(ok, that one was a joke)

Any other words of advice?

I'll be reading through the Haynes manual again (for what that's worth) but if anyone has any experience with this job and could give me some pointers...well, I'd appreciate it, might even drink a beer in your honor after finishing the job.

Peace,

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95 Red YJ, 4.0, Auto, hard-top, stock, daily driver (for now)

93 Black YJ, 4.0, 5 speed, rebuilt motor/tranny/transfer cas, lifted, herc'd interior, lights, chopped fenders, custom "pin stripes" and "beauty marks", etc...*sold*

80 Red CJ5, fully restored, all original *sold*
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Unread 11-22-2007, 08:28 PM   #2
pasinbuy
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If it is rod bearings you may be biting more than you can chew. Bad rod bearings mean bad crank..Two surfaces mating and all that crap.

I would do more research to find exactly where your problem is. The old time used car salesman would use oil soaked leather around the rod bearing to fix a car to sell. It would last 20 to 100 miles until it wore out then the problem occured again, only a little worse. Get a new short block, cheaper and easier. Plus you are new again, or have your motor rebuilt. Rod bearings are not a quick fix that lasts.

Yes, on the main seal as long as you are there.

Thanks for the beer.
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Unread 11-22-2007, 11:05 PM   #3
goatboy
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Agree with pasinbuy... very probable that you are not gonna get away with simply replacing the bearings...you will, at the least, have to have the con rod sized, probably will need to either have the crank ground to minimum .010, possibly more, and if you're gonna go thru all that, just bite the bullet and rebuild the engine...have the head gone thru, when you're done, you've got a new engine...only time folks just change out the bearing is when they want to cheap it out and don't care if it's gonna last too long, cuz it ain't...
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Unread 11-23-2007, 12:47 AM   #4
swedishdwarf
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I agree with those guys. If you are looking at a tight budget you'll be much better off buying a used motor than just changing out the rod bearings.
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Unread 11-23-2007, 02:46 AM   #5
redjeep669
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for the most part i agree. jeep 4.0's seem to be forgiving when it comes to the rod bearings but if this has been an ongoing thing you're probably out of luck. the crank will spin the new bearings sooner or later. but i've seen ring and bearing jobs i was sure wouldn't last go for 30-40k. the CORRECT thing to do is undersize the journals and true the crank. the CHEAP thing to do owuld be the bearings and cross your fingers. i guess it's not that bad. worst case scenario the new bearings spin and you're out 30-40 bucks. as far as ease, it's pretty cut and dry. drain the oil, drop the pan, pull the caps, and drop the crank. you'll have to move a few other things but that's the gist of it. i'd consider pulling the whole piston/rod assy down and doing a re-ring (if you can pull them down through the bottom - i've rebuilt like a dozen of these but i can't remember if they can be done in that manner since i bench build them).

oh, btw, the RIGHT thing to do here is a stroker.
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Unread 11-23-2007, 03:29 AM   #6
flysyj
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i bought a 91 comanche-brand new-4.0ho..in ten thousand miles, it develloped a rod knock..i brought it in and they replaced the bearings on warranty, ten thousand later..one more time..ten thousand later a whole new long block..you can change em, but it's really the crank that is bad, it might work, but it is only a patch and yes i would change both seals~my two cents~fly
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Unread 11-23-2007, 07:57 AM   #7
rezalien
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options

thx for the advice! From what I'm understanding here are my options

1. replace the bearings (patch job at best, might or might not last)
2. swap in a used motor (same concept to me...current motor only has 73k on it, why would I put a motor in with higher mileage that I know nothing about)
3. pay for a rebuild
4. drive it like it is, buy a used motor, rebuild it myself, swap it in when I'm done
5. Stroke it!!...would have to upgrade to 8.8 , then might as well SOA , SOA would require at least 35" tires , might as well lock it while I'm at it = DIVORCE and 15 yrs of child support . Naw, that would be too expensive at the moment.

I've got some thinking to do...would welcome any other opinions.
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95 Red YJ, 4.0, Auto, hard-top, stock, daily driver (for now)

93 Black YJ, 4.0, 5 speed, rebuilt motor/tranny/transfer cas, lifted, herc'd interior, lights, chopped fenders, custom "pin stripes" and "beauty marks", etc...*sold*

80 Red CJ5, fully restored, all original *sold*
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Unread 11-23-2007, 08:22 AM   #8
bogger jeep
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here is what i did. rear seal leaking. while the pan is off , icheck a bearing. wow ,the crank is grooved and bearing look to have 900,000 miles on them. reason was my timing chain went out and rubbed on the case and put aluminum fileing in oil. the fix. may only last a week . i use emery cloth on the crank to get it a little smoother and put in new rod ans mains and replaced rear seal. [not easywith thecrank in]. that was 3 years ago.still no knock and it runs fine. its a wheeling jeep only not a DD so it doesn't get a lot of miles. but mine wasn't knocking. if its a crank knock, the bearing has probibly spun and the crank will have to be turned. or you may be able to emery close the crank and mic the crank and get an over size bearing and get by for a little while.but it would be a short term fix at best. stroker would be best but i have been through divorces and wouldn't wish that on anyone. good luck...
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Unread 11-23-2007, 08:29 AM   #9
JohnRodriguez
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rod bearings are fairly simple to change. is the sound you are hearing is a double tape??? It could also be a main bearing, piston slap or a exhaust leak. A exhaust leak will sound like someone is lightly hitting your block with a small ball peen hammer. the piston slap will sound like a rattle if any of the lands are broke. especially at higher rpms. A main bearing will make a progressive/continuous sound as the rps increase, and will almost disappear if you let off the gas and remove the load from it.
When you remove the rod ends, the lower bearing should be the one with wear on it, very slight copper tint from the babbit wearing tru if it is wearing normal. other wise it will look like hammered dog **** if it is bad rod bearings. if it is bad rod bearings and the crank have score marks from dirt in the oil, then you could put some very undersized bearings and hope that they will conform and fill the voids when replaced.
You never mentioned what the oil pressure did when you first started the engine from a cold start. does it run quite and then get noisy when the oil warms up? if it does than the mains might be the sound. also if the con rod journals had score marks then the mains have score marks, as the oil has to go tru them first to get to the rods. to replace them just loosen all the main caps and remove one at a time the cap that you are going to do. use a flexible gasket scraper, about 3/4 inch wide and use it to push the upper bearing out. look for the indexing tab and don't try to push form that end. when all the bearings are replaced, then snug the caps down and thighten them.
As you can see, diagnosing this type of problem is very hard if you have never been tru it or really heard the sound before. You might consider finding a older mechanic who has more experiance and could help you determine what the problem actually is. other wise just pull the pan off and look around, it's not a very hard thing to do on a jeep.
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Unread 11-23-2007, 09:05 AM   #10
rezalien
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It's definitely not exhaust leak, not the normal valve tap either. It doesn't seem to be a double tap, it's in sync with rpms.

I put a stethescope on it and the place where the sound is the loudest is at the rear main seal, in between bellhousing and motor.

Oil pressure on cold start starts at 0 and rises to 60 in < 60 seconds. Stays there regardless of rpms etc... Motor sound beautiful at startup, takes about 2 mins for the knock to develop, knock goes away at even the slightest throttle (in neutral or in drive), knock comes back at idle.

I'll probably just drop the pan and have a look before I go and order any parts, that might lead me in the right direction.
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95 Red YJ, 4.0, Auto, hard-top, stock, daily driver (for now)

93 Black YJ, 4.0, 5 speed, rebuilt motor/tranny/transfer cas, lifted, herc'd interior, lights, chopped fenders, custom "pin stripes" and "beauty marks", etc...*sold*

80 Red CJ5, fully restored, all original *sold*
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Unread 11-23-2007, 11:07 AM   #11
goatboy
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I've never had any problem discerning a rod knock from an exhaust leak or anything else, and I've had a few of my engines over the years knock on me...I think your game plan is real sound, do a good lasting fix now, start thinkin' down the road on that stroker...if you buy a used engine now, you are absolutely correct that it may not be any better than yer own engine, but it will allow you to rebuild and modify your own engine to your heart's delight and at a more relaxed, fun pace...when you finish with your dream engine, you pull the temporary engine out, and either sell it or rebuild it as a spare...
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