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Unread 05-28-2011, 10:05 AM   #1
Diamond-x
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1991 XJ Cherokee 
 
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Location: Socal
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Rod Bearing Replacement

My 4.0 liter stroker has had a slight knock since day one. I always thought it was the valve train, either a rocker or lifter. The motor has always run strong with no problems just a slight noise.
A few Saturdays ago I drove it about 50 miles and the noise was getting progressively louder. Under accelleration or decelleration it was getting very noticable. I arrived at a friends house and shut it off for about 20 minutes. When I started it backup it knocked loudly 4 times, until the oil pressure built in the journal.

I knew something wasn't right.

Here's a video after I dropped the pan, if you turn the volume up you can hear the bearing click as I move it back and forth:

http://www.flickr.com/photos/1513452...in/photostream

I removed the bearing and here is what I found:



The damage is evenly spread over the entire bearing surface, which leads me to believe it is from improper fit or overheating. or both. The engine has gotten hot several times.

The journal had bearing material on it, but also seemed to be evenly distributed. There were no deep grooves or scratches.



I then took some Emery cloth and wrapped it loosely on the journal, securing it with some duct tape. Using a tie strap I smoothed the journal, moving the crankshaft to multiple positions. I worked on this for over an hour.



I then assembled it dry with some plasti-gauge, it is well within specs. It seems that very little damage was done to the journal and only deposited bearing material on it.

I reinstalled the oil pump and pan after cleaning with brake cleaner. I was able to reuse the oil pan gasket and got lucky, it doesn't leak. After it goes through a few heat cycles I'll change the oil and filter.

It sounds better than it ever has. The knock is gone. I've been babying it since the fix, atleast until I get a couple of hundered miles on it.

I have around 15,000 to 20,000 miles on this engine. I drive it hard, have revved it up over 5,000 RPM several times prior to the failure (which probably explains it) I built this stroker and enjoy it every chance I get.

I know I'm rolling the dice when it comes to longetivity on this solution. Most mechanics would recommend pulling the engine and surfacing the crank. I didn't want the extended downtime and only had 4 loud knocks on the bad bearing, it's a calculated risk.

We'll see how it works out.

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Unread 05-28-2011, 09:17 PM   #2
psychoteen101
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Yea, its a risk, but atleast you took all the steps you could without having to pull the motor and have everything resurfaced. Only thing different i would have done was replaced the oil pump and pickup tube instead of using the old stuff. Hope it works out.
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Unread 05-29-2011, 11:41 AM   #3
Diamond-x
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Oil pump was replaced when I rebuilt it 20,000 ago. I had to remove it to get to the bearing (#5), It's fine.
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Unread 06-10-2011, 08:03 AM   #4
Jason_alex
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Howed it turn out?
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Unread 06-10-2011, 03:16 PM   #5
Diamond-x
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Quote:
Originally Posted by Jason_alex View Post
Howed it turn out?
No problems yet, knock on wood.
I've been driving it regularly to work and have put about 3-4 hundred miles on it. I've changed the oil and filter, the oil had a little residue in it but not much. I've also been into the throttle 100%, for an extended period. The engine is running great and makes no strange noises. I must have had this issue since the day I fired it up.
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Unread 06-10-2011, 04:10 PM   #6
Jason_alex
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Thats good to hear, where you having any problems with your oil pressure being low?
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Unread 06-10-2011, 06:19 PM   #7
Diamond-x
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No, the oil pressure has always been good.

The Jeep gauge reads +60 psi at idle at cold startup. +-20psi when warmed up at idle.

I had installed a new HP oil pump when I built the engine 15,000 miles ago.
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Unread 06-10-2011, 07:20 PM   #8
cruiser54
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This is certainly one to follow. Kinda scary but let's hope for the best.
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Unread 07-29-2011, 02:16 PM   #9
Diamond-x
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Still running strong, no knocks yet! I've put approx 1,000 miles, sometimes under obscene acceleration.
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Unread 08-24-2011, 06:52 PM   #10
00ClassicXJ
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Just found this thread and feels exactly like what is happening to me. I just bought a 00 XJ. When the engine is cold, runs fine. No knock. Once it heats up oil pressure drops and knocks to high hell. Once ive driven for a while, oil pressure drops at idle but pops back up under acceleration. At first i thought it was a busted boot, but the knock has nothing to do with steering. Can anyone help with what may be going on?
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Unread 08-24-2011, 07:01 PM   #11
Diamond-x
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Quote:
Originally Posted by 00ClassicXJ View Post
Just found this thread and feels exactly like what is happening to me. I just bought a 00 XJ. When the engine is cold, runs fine. No knock. Once it heats up oil pressure drops and knocks to high hell. Once ive driven for a while, oil pressure drops at idle but pops back up under acceleration. At first i thought it was a busted boot, but the knock has nothing to do with steering. Can anyone help with what may be going on?
This is a classic description of worn bearings. As the bearings wear they become thinner (bearing clearance increases) letting more oil pass than they should. When cold the oil is thicker and reduces the knock, when the oil heats it thins and the knocking is more noticable.
This symptom is systematic for higher mileage engines, it's time for a rebuild.
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Unread 08-24-2011, 07:23 PM   #12
00ClassicXJ
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Has only 103k miles. Im already starting to get a headache. Bought this just a few weeks ago sight unseen as a second car. I dont have the resources nor the time to fix this on my own. Should i be able to take this to any reputable repair shop? Anyone have a rec for a mechanic in dallas, TX?
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Unread 09-13-2011, 03:05 PM   #13
Diamond-x
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Approx 1,500 miles since replacing the rod bearing, although it's parked for my rocker upgrade. No knock and still running strong.

FYI.
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Unread 11-15-2011, 04:55 PM   #14
Diamond-x
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So.......

I spun a distributor gear, by spun I mean there was a radius on one side matching the cam gear. So the distributor was no longer turning. I dropped the oil pan, cleaned it out and popped a new distributor gear on. Within 10 minutes the new distributor gear was trashed. It seems that my cam gear was worn due to inadequate oiling, according to a shop who is well versed in the 4 liter engine. It got so small that it tore up the distributor drive gear. Cylinders and pistons seem fine.
I have a stock oil pump, not a high volume. Also, the rod bearings supplied by Summit did not have the squirt hole which provides lubrication to the cam. There is no oil galley that provides lubrication to the cam gear.
Back to the shop it goes for new cam, lifters, bearings (cam,main,rod), timing chain, rod bolts and rings. I got a quote for $500 plus parts.

It ran 3 years to the month somewhere around 25,000 miles.

I thought I should share this information.
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