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How deep to go with my resto? (The little ol' 4.0 that might)

739 views 6 replies 4 participants last post by  zakleeright 
#1 ·
Doing frame-replace resto on 97 TJ 4.0 AX-15 Progress to date:

• Shook my rusty frame til all the parts fell off into shelves, bins, and baggies (thanks, Soundgarden)
• Sourced a straight, no-rust frame
• Lop off 2.4L motor mounts, made jig to place 4.0L mounts, welded on
• Frame has Por-15 & top-coat, Eastwood inner frame coating
• DPG OME/JKS 2.75” susp. Lift. 1.25” BL is ready when the tub is
• New ball joints, linkages,u-joints, axle seals, brakes, etc, etc
• All hardware cleaned/prepped (+1 for vibratory tumbler) or replaced
• Pretty frame now rolling on 33s in a shack near you.

Belly pan on, ‘bout ready for a hunk of noisy iron and some gears, so...prep engine/clutch/trans/harness so I can toss it on the frame. Then slap the tub back on, and go tear it up in sand, mud, rocks, ruts, trees, and bad decisions.

~250k miles – maintenance unknown, but sparked right up and purred sweetly before purchase ‘cept for the crack header leaks...and the belly pan/tranny hanging on by flaky orange metal shards and hope.

And now. Beer in fridge. Tranny on a jack somewhere. New header to replace its cracked brother waits in a bag behind me. 4.0 on engine stand...all proud of its slightly rusty self - sittin there all “perfect work height” and damn near nude.

1. So, how could I NOT change the rear main seal...and front seal. Well, while that’s off, why not get some Plastigage and check crankshaft main bearing clearance?
QUESTION: The FSM says 2 methods to support Crankshaft while doing this. Preferred: .010” shim on bearings adjacent to the bearing to be checked. Alternate: Support crank weight with a jack under the counterweight adjacent to the bearing being checked. Can anyone with experience school me on this? Am I wrong that it seems fairly easy, given that I’m right there staring at it?
QUESTION: FSM says that when reinstalling front main seal, “Apply a light film of Perfect Seal, or equivalent, on the outside diameter of the seal.” What? Is that the toilet sealing stuff?!​
2. Timing cover may as well come off, to verify < .5” of chain slop.
3. Dang, except for pulling rocker arms/push rods, the 1st 15 steps of head removal are done, so...get a kit with new bolts, gaskets, etc. Now I can check cylinder wear, valve wear, new gasket, etc.
• I lack a few specialty tools, so maybe...$350 for that? (Dial gauges, an inch-lb torque wrench,...)
• If there’s only a little wear, slap it all back together w/new gaskets, timing chain and go. But at 250k miles, what do I expect? (wear...I expect wear)​
4. Hmmm. I see reman short blocks for $950. Compare that against tools and replacement parts...hmmm.
5. Love the idea of doing my 1st engine rebuild (if needed), but also itchin’ to make bad decisions in mud n ruts. One friend says, “dude...just slap that beast in and let’s go!”
6. long blocks for $1500. Built stroker for $6500...LS crate motor for $9000...wait. Wake up. Psycho-analysis for existential crisis - $145/hour.
7. Maybe I can borrow/rent (or just buy)the specialty tools so I can measure everything, and then I’d know the good, the bad, and the ugly. Feeling my way thru this as I go.

Thoughts? Ideas? Prayers?
Thanks!
 
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#2 ·
I know that hole you looking down!

How long do you want to spend on the motor? If you end up rebuilding your own, which is a great experience, expect it to take longer than you expect. And it will cost more than you expect. If you are with a month or two, go for it. Your wait will be at the machine shop and waiting for parts. Last time I had a block worked, I called after a month of hearing nothing, and they said they didn't realize it was a rush job. Had a 4.0 head reworked at another shop for a 258, and that was only two weeks.

If it was me, I would just get the long block and be done with it. If you want more power then you can chase the engine swaps. And if you are looking engine swaps, why not a diesel?

However, have you done a leak down on the old engine? That will give you some of an idea of the health of the old engine and whether or not you even need to do anything other than gaskets.

As far as checking the main bearings, I believe you should be able to just spin the motor upside down on the stand and not worry about supporting the crank. FSM is probably for checking in the vehicle, but I admit, I am speculating.
 
#4 ·
I'd go with a reman long block. One and done.

My 4.2 has blowby and almost 200K miles. It runs well but fills the air cleaner with oil if I run at highway speeds for a long time. Even though a motor starts and runs well, doesn't mean it's in good condition.
Knowing my motor was tired, and I plan on keeping the Jeep for a long time, I bought a rebuildable 4.2 core. That was over a year ago. I had the motor all apart within a week but the bare block is still on the engine stand awaiting a trip to the machine shop to be cleaned and checked.

If you want to be able to play in the mud and ruts any time soon, I strongly suggest the reman long block. Thinking that a motor with 250K miles will have "only a little wear" is unrealistic. You'll find plenty of other things that need attention as you assemble your Jeep that will slow you down. If you have a regular day job and are doing the build in your spare time, it could take months to rebuild your current motor. You still have quite a way to go with the rest of the build so why add the time to rebuild an engine to your wait.

A re-manufactured motor should come with some sort of warranty. For me, I'd want to deal with a local engine builder that has a good reputation. Check with your hot rodder buddies and check the online reviews of whatever companies or shops you get recommendations for.
Most auto parts stores can order a re-man motor, but those motors are "generic". I'd rather deal with a (well established) person or a shop that has their reputation on the line.

Let us know what you plan on doing and post some pics.

Good Luck, L.M.
 
#5 ·
Thanks for the input guys. Tgood - you gave me a "duh' moment. I think your instincts are good. My whole reason for doing this is because the engine is on a stand and can rotate to do the seals, etc. So all I need is plastigage. Haven't done a leak down test, but will check the FSM on that this morning before I leave for shop.
Digger - yeah...crazy day dreams aside, I'll just stick with a stock 4.0, and I'm leaning toward a long block now, so I can get this thing back in the woods. i have TONS of pics, but will curate it down to a select few and figure out how to post them on here. Gonna go out today and finish up a couple little things, and feed the stray dog that showed up at the shop.
Yea...working on this most weekends - I'm just shy of 170 man-hours at this point. That's me and another amateur - so things take longer to figure out sometimes, and its the weekend so we're not rushing around...breaks and, at some point, beverages are involved.
 
#7 ·
before and after

Day 10 - all parts removed from frame - bagged and tagged.
Day 42 - rolling chassis - belly pan and bumpers are now on

hundreds of pix before/after/in-between these, in hopes of helping myself and others down the road. maybe I'll post a story board to the build section.
Cheers
 

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