unclecameron

So I bought this GC with the 4.0 and it was leaking oil, badly, and the bottom end was knocking. I heard the previous owner high-centered it on a stump, never put it in 4-wheel drive, and just floored it until something happened, apparently it was redlined for awhile. Also, when she hit the stump, the radiator broke the top corner, about 3" worth, and then pumped out all the water rapidly. So it was running at redline long enough to spin a brand new right rear tire down to bare threads turning to steel wool before it quit.

Then she hiked to town around 7 miles, and since she was off her meds, she doesn't remember any of this, and woke up sometime later to a dead Jeep that was towed home.

I decided to buy it, knowing it may have engine issues, but decided to see if there was damage to the rest of the running gear, so fired it up, knocking and all, and proceeded to drive it down the road about 45 miles an hour for about a mile, puking oil and smoke, knocking the whole time, then threw it on the trailer since it drove fine and brought it home. When I pulled the intake manifold off (because you couldn't see the problem tucked up in there, I found the top of #6 connecting rod sitting outside a hole in the block on the edge of the bellhousing! Here's a picture:


That's about where the rod was sitting when I reached down, picked it up and set it on the bench, when the motor was still in the rig!

Keep in mind, the thing was still driving down the road!! The piston had dropped down in the bore and was just sitting there, but didn't get down into the crank. Meanwhile, the crank basically melted the bottom of the rod and deposited it in the pan in a million chunks, and it torched the journal, here's a picture of the bottom end, notice the black looking journal with serious cracks and galling, and the fact you can see the shop floor through the block


Now (thanks to a lot of people on this forum's help) I found a donor block, put a set of pistons in it, surfaced the head, cleaned mic'ed and checked the crank, and the thing runs like a top, but I can't really think a tougher motor than one that would run with a gaping hole in the block, #6 piston skirt torched, crank hozed, bottom half of rod and bearing in pieces in the oil pan, and still happily driving down the road at 45...you got me sold on these motors

And thanks again all for the help, couldn't have done it without you And if anyone asks if the old straight 6 4.0 is a good engine... you've got at least one 'yes' vote from this raised-from-the-dead now daily driver.

bigbuk29

ONLY IN A JEEP!!!!!!!!!!!!!

5-90

Hey - can I talk you out of those main studs and that crankshaft brace?

The durability of the AMC six borders on legendary. During the recent C4C debacle, the Jeeps with the 6-242 were harder to kill than even the BMW or Benz! I got one report that the 6-242 ran just fine for about an hour and a half with the oil completely replaced by waterglass (sodium silicate in solution.)

!

(The report came from someone who I've been dealing with for years, and have no reason to distrust. And he has no reason to lie to me.)

I had a SGEF (Sudden Gratuitous Existence Failure - thanks for that, Bob Surface!) of the oil pump in my 1987 some years ago. This happened at 220K on the clock.

I tried to limp home (I was on a mountain road - Highway 35, if you're in the SF Bay Area, south of Highway 9) and made it an extra five miles.

Then, the #6 connecting rod tried to leave through the side of the block (I later found this out) and blew a hole in the skirt big enough to pass my fist through. Scored 11/13 crankpins, collapsed 9/12 tappets. Bent no pushrods, caused no damage to the camshaft!

I replaced the crankshaft, replaced the #6 rod (piston was fine,) replaced all twelve lifters, and used JB Weld to stick the chunk of iron in place that blew loose.

I did not do anything to the cylinder bores (at 220Kmiles, there was 0.0005" of ridge - absolute height - at the top of the bore, and no noticeable belling of the cylinder.) Hell, I didn't even change the rings - if I had, I'd probably still be driving it!

With the old rings, old camshaft, no bore work, no head work, and a "major in-place" overhaul (I didn't pull the engine, either...) Clyde was off and running again, and I put another 80kmiles on the engine after that.

(I was able to limp around on the engine until the #6 rod happened to get in a place where it wedged the #6 crankpin against the block wall - which is why the fist-sized hole blew out.)

I've got an 88 that's downchecked for a refit and overhaul of the engine management - at an estimated 350kmiles. (I say "estimated," because I've been through four of the BA-10/5 transmissions before I got the AX-15 in, and I hadn't finished the swap before things started getting silly. I don't know how many miles I'd put on it after the swap.) No, I'm not going to get rid of this one - I'm going to fit it out as a work/travel truck (I drive cross-country about once a year to visit family, we're also in Indiana and Georgia,) and a partial cosmetic refit is in the works - I want to redo the IP using aircraft gages, because I like them and I'm used to them (had my pilot's ticket before I got my driver's license.)

But, even with the oil starvation, the lifter crowns had not been depressed - it's just that the lifter plungers wouldn't retain oil and pump up anymore, when I checked them.

In thirty-odd years of assorted mechanical work, I've yet to find an engine that can take more abuse than an AMC - both the "Modern Era" six and the Gen-II/III V8 engines have positively amazing durability!

Did you know that all AMC Gen-II/III V8 engines came from the factory with forged internals?

mrfajita

A 4.0 with gear driven camshaft and forged pistons would never die!

wildspear

On New years eve I was driving my wifes Cherokee (I-6 4.0L). It had a tapping when we bought it but it ran fine so we didnt worry about it. I had stopped at a stop sign. I started pulling and heard a noise and the jeep started running really rough. I drove it home ( about a mile) and parked it. Once I got a chance to look it over I found that the #3 piston was totally destroyed. The wrist pin must have broke and the arm beat the piston to death. Still would start (ran really bad), no hole in the block.

Can't beat the Jeep I-6!!!!

1slo_camaro

Need another motor? Ill have a spare for super cheap if your close to MD

unclecameron

@5-90: you can have anything in the picture, just PM me and pay the shipping

I also have an idler pulley if anyone wants it...same deal

@1slo_camaro: I found a donor bottom end, which (after a rebuild) is now humming along fine in the rig, which is now a daily driver again..

I put Sealed Power pistons in it, and had the new donor crank mic'ed, cleaned and micro-polished, along with the head resurfaced. Plus a new oil pump, rings, rod's mic'ed and gasket set, and the mains were right in spec too, so I guess the thing should run forever now I think I have about $800 in the whole rebuild, including the donor bottom end, so hey, that can't be too bad, especially because I chose decent replacement parts so I wouldn't have to do it again anytime soon.

Now if I could figure out why it hard shifts into 2nd sometimes...I guess maybe at 152K on the clock, along with the stump excursion, maybe the tranny's just getting a little tired. I serviced it with a new filter and oil, but I'll try to milk it awhile longer. Still, I can have the tranny rebuilt for roughly 1/5th of the cost of doing the same on my Mercedes, sheesh!