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anthrax323
November 6th, 2017, 11:16
As luck would have it, right after I get my 2001 XJ back on the road, I've developed a significant rod bearing or wristpin knock... It'd been around in some form for about 10,000 miles, and would largely go away once warmed up, but after accelerating to pass someone on the highway the noise became MUCH more substantial.

I know that rod bearings are easily accessible just by dropping the oil pan, but I'm more afraid that it's ultimately a wristpin failure. Is there enough room to pull the pistons down from the underside (with the crankshaft still in-place) so I can replace the wristpins too? Or would I be looking at pulling the head at that point?

RCP Phx
November 6th, 2017, 11:41
You have to pull the head.

anthrax323
November 6th, 2017, 13:17
Looks like lifters are going on the list too then. Thanks man.

BCKNBLK
November 7th, 2017, 22:16
Agreed, you have to pull the head, which is fairly straightforward. Keep in mind though, that it would not be wise to replace these items for just one cylinder. You are far better off replacing the bearings and/or wristpins for all of the cylinders. If the engine has not been opened up before, you most definitely are in for a surprise or two. How many miles are on it?

8Mud
November 8th, 2017, 22:03
Why not pull the pan, inspect the bottom of the pistons. Have somebody rock the harmonic balancer bolt and watch for play between crank movement and piston movement, You'll likely be able to see significant wrist pin slop (or hear it).

My bet is connecting rod bearings, I've had to swap them out on three different XJ's so far. I have found loose rod cap bolts. I plasti gauge mine, top and bottom of the bearing. The top bearing seems to wear quicker (more) than the bottom does.

A little tip, take the pan off, liberally spray down the whole bottom of the motor with brake cleaner, let it drip and dry overnight. Trying to do it with oil dripping in your face sucks. Tip two, plasti gauge melts in oil, rods, caps and bearings have to be squeaky clean. Tip three, a little loose is netter that too tight. Trying for perfection with over sized bearings is likely unnecessary, a thousandths larger than optimum clearance isn't going to hurt anything. Tip four, check the right side of your block for over sized bearing codes.

Getting the pan off without screwing it up can be a pain, it will save time in the long run if you don't bend the pan lip up too much.

anthrax323
November 9th, 2017, 16:09
Thanks for the tips, guys.

Where exactly on the block are the bearing codes? Assuming near the bottom on the passenger side, but thanks to bad oil filter adapter O-rings, there's at least a 1/8" cake of mess all over the place. Narrowing it down will save some digging.

I'd forgotten that I bought a new oil pan gasket and RMS a few years ago (when I planned on fixing the latter), so I'm good to go other than buying the bearings.

RCP Phx
November 9th, 2017, 17:04
There are no codes on the block, any machining that would ever be done(besides boring/decking) are done to the crank.

Jeep Driver
November 9th, 2017, 21:19
There are no codes on the block, any machining that would ever be done(besides boring/decking) are done to the crank.

Yes there are.

Over/under codes on some engines.

http://street2mud.com/webfiles/AMC%20Engine%20codes.pdf


May not be common today but it certainly was not that long ago.

RCP Phx
November 10th, 2017, 08:21
Yes there are.

Over/under codes on some engines.

http://street2mud.com/webfiles/AMC%20Engine%20codes.pdf


May not be common today but it certainly was not that long ago.

Worthless! Where's anything that applies to Cherokee's or Comanche's?

anthrax323
November 10th, 2017, 08:40
I'll be picking up a proper micrometer set, so no big deal on the tag. Given that it's a 2001, they might have refined their manufacturing process to the point that tagging for over/undersized bearings became unnecessary.

That being said, tolerances should be ideally between 0.001 and 0.0015" right?

*EDIT* - Everything I'm reading points to:
Desired: 0.0015"-0.002"
Allowable: 0.001"-0.003"

Here's to hoping the damn journals aren't f***ed.

RCP Phx
November 10th, 2017, 09:53
No real issues either way, you can have your crank turned or possibly get a exchange crank. We accepted as a good core anything to .030" under, after that we would just weld-up the journals and start again!

Green XJ Jeep
November 10th, 2017, 11:10
Worthless! Where's anything that applies to Cherokee's or Comanche's?

A different letter represents each part and the modification. The letter is located on the boss directly above the oil filter on six cylinder engines, on the valve cover tag on V8 engines. One or more letters may be present:
B- 0.010" oversize cylinder bore
C- 0.010" oversize camshaft bearing bore M- 0.010" undersize connecting main bearings
P- 0.010" undersize connecting connecting rod bearings

anthrax323
November 10th, 2017, 12:26
No real issues either way, you can have your crank turned or possibly get a exchange crank. We accepted as a good core anything to .030" under, after that we would just weld-up the journals and start again!
Yeah... If the crank needs machining, the engine needs to come out. If the engine comes out, an LS2 is going in its place. I'm just hoping it's good so I can limp the engine along for a month or two until the garage is finished, and funds are available for the LS2 swap.

I picked up a 2001 M5 a few months back, so now everything in the stable needs at least 400hp. Because reasons.

RCP Phx
November 11th, 2017, 08:35
A different letter represents each part and the modification. The letter is located on the boss directly above the oil filter on six cylinder engines, on the valve cover tag on V8 engines. One or more letters may be present:
B- 0.010" oversize cylinder bore
C- 0.010" oversize camshaft bearing bore M- 0.010" undersize connecting main bearings
P- 0.010" undersize connecting connecting rod bearings

That is a AMC document which means it might apply if you own a 84-86!

Jeep Driver
November 11th, 2017, 09:03
That is a AMC document which means it might apply if you own a 84-86!

There you to being arrogant again.


Chrysler bought AMC in '87 and continued using AMC parts through '89. Chysler didn't retool until '90 (IIRC).

I had a '89 that was a mixed bag of AMC and Chrysler parts.

No, may not apply to the OP's 2001, but the OP brought it up. Your blanket statement that it does not apply to XJs is incorrect.

The entire world does not revolve around the OP, nor you. Others may read this that do have an AMC........just a point of interest.


As for the OP's desire for a cheap-out in-frame...........waste of effort. He's 90% of the way there, pull it and rebuild it.


As for welding up a journal? 4.0 cranks are still dimes-a-dozen, another dumb idea.


And further, at this point, it would not be uncommon to find any year block in any year XJ.

Green XJ Jeep
November 11th, 2017, 10:03
That is a AMC document which means it might apply if you own a 84-86!

Those codes were used up until the end of 4.0 production.
Chrysler didn't toss a system they still used and in special engines still use.

All manufacturers have used or still use similar codes.
The ones that don't any longer are the ones that have fully automated engine production and toss out of spec parts instead of machining them to work.

RCP Phx
November 11th, 2017, 10:15
As for welding up a journal? 4.0 cranks are still dimes-a-dozen, another dumb idea.

I've welded 1000's of cranks! It used to be a common practice specially for increasing the stroke!