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  #1  
Old February 26th, 2017, 13:28
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Weasel Weasel is offline
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Rod Bearings

I've read a bunch of the threads. I have a low end knock in my engine. I pulled the oil pan, changed the rear main and inspected the flex plate. All bolts were tight and no cracks, sprayed it with dye penetrant 4 times.

I also plastic gauged the mains and rod bearings while I had the pan off. They all checked out okay no huge issues that I could see for having 135k on the engine.

Pics are here:
https://goo.gl/photos/R8qdPEYWdcMxsKHx5

So I reassembled and torque all the bolts and sealed it all up. It was good for about 2 months, nice and quiet.

And now it's rattling again. Also the oil pressure has been dropping near zero at idle. So I'm getting ready to take the oil pan back off. I'm looking to install ARP rod, main studs, and a higher flow oil pump. Yes I have read all the threads on the higher flowing pump.

But questions is do I mess with changing the rod bearings? How do I size them? Also on the pump is a mopar pump worth the extra over the Melling? I saw the Hesco pump but it's 3x the cost of either.
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Old February 26th, 2017, 13:34
N8N_99xj N8N_99xj is offline
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Re: Rod Bearings

I have a set of stock size rod bearings in my junk box if you want to try them

I was going to roll them into my 99 but I'm going to end up scrapping it instead.
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  #3  
Old February 26th, 2017, 13:42
RCP Phx RCP Phx is offline
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Re: Rod Bearings

Sounds like the cam bearings are worn too!
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  #4  
Old February 26th, 2017, 14:45
JeepNoob JeepNoob is offline
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Re: Rod Bearings

I foresee a LOT of Plasti-guage in your future... Sizing out rod and main bearings is generally something that most guys do with the engine out of the vehicle and on a stand. Partly because gauging rod bearing clearances and replacing rod bearings is easier done with the cylinder head off and the rods out of the engine... You should be able to find main and rod bearing clearances in any good workshop manual. You can get bearings in various different thicknesses, but as a rule of thumb, an oversize bearing is gonna to add bearing clearance and an undersize bearing is going to decrease bearing clearance. I'd definitely take N8N up on his offer just so you can get a base-line with stock bearings and go from there. This video shows a pretty good example of checking bearing clearances- https://youtu.be/rZtDLw7Tge4

Last edited by JeepNoob; February 26th, 2017 at 14:53.
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  #5  
Old February 26th, 2017, 19:03
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Weasel Weasel is offline
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Re: Rod Bearings

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Originally Posted by RCP Phx View Post
Sounds like the cam bearings are worn too!
why would tightening up the main and rod bearings make it go away?

I'll check the links, thanks. N8N, pm coming your way. Not super excited to do a crap load of work on this thing, that why I have a crawler and racer, lol.

Sorta what I figured, install new baseline, plastic gauge and adjust as needed.



And whether it has a hill of beans to do with anything I'm not running Mobil 1 in anything anymore. Bought the Jeep of my Dad and he changed oil before or right at 3k with full synthetic since it was new. This is the second of his vehicles to have excessive wear issues seemingly early in mileage.
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Old February 26th, 2017, 20:16
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Re: Rod Bearings

Don't do main studs without a main line bore. Don't do ARP rod bolts without resizing the big end. If installing new bearings made the rattle go away for a bit, then either the mains or rods are out of round, or the crank is. Plastigauge is a poor way of measuring but it'll get you close. Replace the bearings with what came out, it is stamped on the back side of the bearing shell. If they are too loose/tight sometimes you can get +/- .001" bearings. Then you can mix and match the + or - size with the standard size to get them .0005 closer to correct. Do not mix say a .010 with a standard. Only a .010 with a .010 +/- .001 Does that make sense? Bad cam bearings will kill oil pressure.
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Old February 26th, 2017, 20:18
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Re: Rod Bearings

Ohh, once a rod has begun knocking, it usually becomes out of round and will need to be resized.
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  #8  
Old February 26th, 2017, 20:41
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Re: Rod Bearings

I didn't replace any bearings last time. I just changed the rear main, and retorqued everything after using plastic gauge, and a overall inspection.

Anyways thanks for the info, more things to think about.
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Old February 26th, 2017, 22:18
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Re: Rod Bearings

Try putting a mechanical oil gauge on it. Preferably a good diagnostic one. I've had sbc's run as low as 10 psi hot idle without noise and they revved over 6k. Also check the crank endplay.
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Old February 26th, 2017, 22:22
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Re: Rod Bearings

Melling pump would be fine too. HV should not be needed and can cause other issues. Always check the gear to cover clearances on oil pumps. Too loose and they won't build pressure/volume like they should. You could have a wore out pump.
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  #11  
Old February 27th, 2017, 11:51
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Re: Rod Bearings

have you considered that it may be piston slap? excessive wear in the lower end of the cylinder where the side-force of the up stroke is the heaviest.
i had it in my 99 with 65K miles on it.
it sounded like a random, sporadic knock from the lower end of the block.
it was most audible with a slightly warmed up engine about 100 - 130 degrees.

some people have lived with it for years with no failures, mine was under warrantee, 2 lower cylinders measured out of spec so the dealer hooked me up with a new engine at the time.

it would be hard to diagnose without pulling the pistons and rods out, but when you drop the pan rotate the crank by hand and check the lower cylinder bores with a mirror and a clean finger in a medical glove. the glove will actually help you feel any kind of texture that might be there. also check each piston for fit in the lower bore, any amount of movement of the piston skirt while in the bore is technically "unacceptable" but isnt necessarily a cause for panic.
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Old February 27th, 2017, 14:20
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Re: Rod Bearings

Quote:
Originally Posted by RCP Phx View Post
Sounds like the cam bearings are worn too!
I had a 4.0 pop a cam bearing out, instantly dropping the oil pressure next to nothing. I heard nothing unusual but did notice the pressure drop and eased on home, a few miles away.
Pulling the pan, to see what had happened, the rod and main bearings were not damaged at all, still measuring out at the optimum clearance.
It took a while to find that a cam bearing was pushed out, evidently not installed right or it was the wrong bearing.
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Old February 27th, 2017, 17:13
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Re: Rod Bearings

Could be piston slap if the skirts are worn. The bore is almost always tighter at the bottom then at the top on worn engines though. Maybe a wrist pin came loose. Press fit pins should have never been invented.
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  #14  
Old February 27th, 2017, 18:29
RCP Phx RCP Phx is offline
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Re: Rod Bearings

Piston slap doesn't effect the oil pressure though!
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Old February 27th, 2017, 19:53
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Re: Rod Bearings

and it should be a constant noise if it was piston slap, not go away and come back, etc? Today the oil pressure was fine, even at idle.

What would be the issue with installing ARP stuff on the bottom end?

just remembered the craptastic exhaust on the newer XJ's that has to be removed to get the pan off.
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