Remember The Jeep That Blew Up 20 Minutes After I Sold It To A Nice Lady? I Have To Fix Its Engine And Drive It 250 Miles By Sunday

David Jeep Drive Blown Engine Head

How do I get myself into such stupid situations? Seriously, why is it 7 PM on Friday and I have to literally repair half of an engine, then get that engine to propel me 250 miles ton Chicago by Sunday. That’s in two days!

I think there are two reasons why I’m in this weird situation. The first is that I communicated to Tracy, the nice lady who bought the Jeep before it unceremoniously blew up on her, that I could have this thing fixed fairly quickly. Yes, the water pump had failed, the engine had overheated, and the cylinder head had cracked, but I’ve replaced so many 4.0-liter Jeep cylinder heads over the years; I could take care of this relatively quickly.

The issue is that I run a car website during the day, travel to car-events far more often than I’d have thought (after all, we’re brand new. I wasn’t expecting automakers to invite us to things this soon), and I have my own junkers I have to mend. So I just haven’t gotten around to fixing the Jeep, which left Tracy stranded nearly two months ago. That’s on me for not managing expectations.

The second thing is (and I think this is something mechanics probably struggle with a lot): I don’t quite think Tracy quite understands the complexity of this repair. I had to yank a freaking cylinder head off a motor! Thats half the damn motor. Plus I had to send that head to a machine shop, which took four days to inspect the part to find out that it was cracked. Then I had to remove a cylinder head off a spare motor I had laying around, then send that into the machine shop to be checked and milled (to get it perfectly flat, just in case). This is not trivial stuff, but I think she’s used to just dropping her car off at the shop, and them having it done in a few days. And admittedly, a shop that took two months to do a repair would not be tolerated.

So I think it’s on me for poorly managing expectations, which I think were quite high in the first place.

Anyway, Tracy is great, and I don’t plan to let her down. So the next 48 hours are going to suck.


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Here’s where I’m at: My cylinder head has been machined and mostly cleaned. I say “mostly,” because the valves are still in the head, so those intake and exhaust ports didn’t get cleaned all the way. No matter, because I’m removing all the valves, since I have to make sure the valve seats are in good enough shape to seal, and I want to replace the valve stem seals.

Here, let me show you what I’m talking about.

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The cylinder head that I’m dealing with sits on top of the engine block, which features a bunch of cylinders with reciprocating pistons inside (see above). Air and fuel enters the cylinders via the intake valve (the big one in the image below) and exist through the exhaust valve (the smaller one).

Valves 1

The two valves slide into a hole in the cast-iron cylinder head called the “valve guide.” Here, you can see the two guides clearly in this image:

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Where the face of each valve seals against the head is called the valve seat. It’s critical that both the valve’s face and its mating surface, the valve seat, are both nice and smooth — devoid of rust or other pitting. If the two mating surfaces don’t seal well against one another, there will be a leak, which could result in poor engine performance.


So what I’m doing now is called valve “lapping” or valve grinding — basically, I just put a bit of valve grinding compound against the face of the valve, then I push the valve against the valve seat on the cylinder head, and then I spin the valve really quickly. In reality, I’m lazy, so I’m actually just pulling the valve against the seat, since I wanted to use a drill to make things quicker (the rubber hose is just an adapter):

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(The square holes in the side of the head are where the intake bolts up, the round ones are exhaust port holes).

This causes abrasion between the valve and head, creating a nice, smooth, silver surface. Here’s the “before” picture:

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And here it is after:

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As for the valve stem seal, that’s a little rubber cup that the valve stem slides into. Here’s a look at a new one and an old one — the seals are inside the valve springs, which close the valves when the camshaft isn’t actively pushing them down (via, in this case, pushrods and rocker arms).

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The seals tend to become brittle with age and heat exposure, allowing oil to run down the valves, through the valve guides in the cylinder head, and into the cylinders, resulting in smoke during startup. I figured I’d replace these just to be safe, since the head was already off.

Valve Stem Seal

Anyway, I have to finish off the remaining couple of cylinders, but once the guides are smooth and the seals are in, I’ll pop the 80 pound-ish head onto the engine (that’s gonna be rough), and then I’ll start putting everything back together. First I’ll install the pushrods and rocker arms, which I have organized so that I know which came from which hole (the theory being that two mating parts tend to wear against one another, and you don’t want to reintroduce a part to a different mating partner, or it’ll have to re-wear to its new mate).

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Once the pushrods and rocker arms are all torqued to spec, I’ll the cylinder head bolts in and torque those to spec. Then I’ll install the valve cover, snug that down, and get on to the exhaust and intake. I’ll bolt those on, following the right torque spec/sequence, then I’ll install a new water pump and thermostat, then I have to put the power steering pump back in, the auxiliary radiator fan back in, the airbox back in, and on and on. Plus, Tracy wants me to swap the shocks, and anyone who knows Jeep Cherokee XJs understand that the probability of me breaking at least one upper shock bolt is 100 percent.

There’s a ton of work ahead, and I have two days to do it. It’s an all-too-familiar situation.

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65 Responses

  1. Now it was a pretty confusing article, the work seems straight forward and the task doable, however what got to me was the Tracy name confusion.
    I doubt Jason has ever sold a vehicle to somebody with the first name of Torchinsky. (-;

    PS Watch your back with those lumps of cast iron.

    1. The fanfiction I’m working on has this as the “meet cute” moment that’ll ultimately see these two get married and Nice Lady will become Tracy Tracy.

      I’m hoping to sell the story to a Hollywood production company to adapt into a charming RomCom. Which actor should be cast to play David?

      1. My buddy’s city councilor is named Bradford Bradford – Brad for short.
        He was named Bradford as a way to keep his mother’s maiden name alive but then his dad ditched them. He didn’t feel like keeping the jerk’s surname so he reverted to his mother’s name. It seems to be working

      2. True Story:

        My mom’s name is Sylvia, and her maiden last name was Crump. After marriage, she became Sylvia Crump Slack. Well…my dad has a sister….named Sylvia….so her name was Sylvia Slack, too!

        But wait, there’s more!

        My aunt Sylvia Slack remarried after her husband died….to a Crump! So, if you’re following along, now we have:

        Sylvia Crump Slack (my mom)
        Sylvia Slack Crump (my aunt)

        “Where are your parent’s from?”

        Louisiana….why do you ask? :-p

  2. I can sympathize. Recently, *both* of my cars decided to crap out simultaneously, forcing me to borrow my very kind parents’ very nice 2020 4Runner Limited. Obviously I needed to get it back to them ASAP, but also I work 45-50 hours most weeks, so Memorial Day weekend was rough.

    Between figuring out why the hell the Miata wouldn’t start after an HLA cleaning (turns out after dozens of forum posts, testing, disassembly, reassembly, talking to the resident gearhead at work, buying new HLAs, realizing that they are were slightly the wrong type, more forum posts, further testing, etc. that I’d reassembled the innermost component backwards, which was causing them to hold the valves open) and fixing the Outback’s crazy temperature swings (new water pump, thermostat, and a flush) I put in many frustrating hours of wrenching and sorely tried my partner’s patience.

    So many things just didn’t go right. Just for a taste, the water pump on the Subaru mounts into M6x1.0 threaded holes in the engine block, which is aluminum. They are supposed to get torqued to 90 and then 120 inch pounds (which is basically nothing) but half the bolts stripped before they even made it to 90. I then removed the pump—shredding the new paper gasket which was RTVed in place—drilled out the holes, re-tapped them at M8x1.25, went to the hardware store for new bolts, made a transfer of the water pump mating surface onto gasket paper (having no time to order a new gasket), painstakingly cut it out with a scalpel, re-mounted the water pump, *still* stripped one of the fucking holes (whose bright idea was it to mount torqued fasteners to aluminum threaded holes anyway?), filled it with high-heat JB weld, came back the next day, re-tapped it, stripped it again, cut the head off a bolt and epoxied it into the hole with more JB to make a stud, waited another 8 hours, and then finally was able to successfully torque a nut onto the stud. It works, and I feel fine about the end product (the epoxy is rated for the heat, it has plenty of grooves to grab onto, and the torque it has to deal with is quite low) but man, getting there was harder than it needed to be.

    Both cars are up and running again, and the 4Runner goes home tomorrow (it would have been sooner but basically my whole family other than me caught Covid, which threw all our plans into chaos) but boy did that suck. I’m used to doing maintenance and upgrades in my own sweet time with one car always available to drive while the other one is up on stands, not emergency repairs and troubleshooting to both cars simultaneously while trying not to alienate my partner and disappoint my parents. I burned up a very nice holiday weekend and I’m only back where I started—even my lifters still tick. It’s fine, life is like that sometimes, but I’m not eager to repeat the experience anytime soon.

    1. Oh yeah, and the fucking factory timing marks on the new timing belt (might as well replace it while the water pump is off anyway, right?) were off by one fucking tooth, making it just barely—but not obviously—impossible to mount. Figuring that one out and then figuring out where the marks *should* have been was a real fun time, let me tell you,

  3. Did it ever occur to you that, if you’ve replaced “so many 4.0-liter Jeep cylinder heads” that maybe it’s not such a great engine?
    I mean, I’ve owned 5 cars over my adult life, and driven a number of crappy family cars before that, and the head gasket job I can remember was Dad pulling the engine out of the ’73 Corolla. And we owned an F10!

    1. The 4.0 is bulletproof… if you actually take care of it.

      David does not have well maintained 4.0’s as a rule. He has engines that sat years without running, that probably got oil changes every 15,000 miles or so – but nobody knows for sure, engines that haven’t done more than idle for 5 minutes for years, engines that only get repaired when it fails catastrophically (like this one,) engines that have minor issues which he starts on and then forgets about for months (the Golden Eagle’s 360,) and so on. Which leads to big, big problems, just like with any other engine.

      It’s a fact that a well maintained 4.0 which sees regular use and has the minor stuff repaired promptly will basically go till the end of time. There is zero question that the engine in this case was already very deeply wounded and has been for a long time before the head warped. The water pump didn’t just ‘abruptly’ fail with bearings like that either, but absent pulley wobble, they are basically impossible to diagnose without a seriously trained ear. I have that trained ear, and I’d say I might get it right half the time on pumps without pulling belts and manually rotating. At best. Which isn’t an excuse for not pulling the belt and checking by hand, but the idiots claiming to be ‘experts’ will scream till they’re blue in the face that’s not how it works and the like.
      So unless you see obvious wobble, you pull the belt (which is a massive pain in the ass,) or you’re in there with a stethoscope and know how to use it, it tends to be a “but it was fine yesterday!” or dumping coolant down the timing face thing. Note: DAVID, ABSOLUTELY DO NOT TRY TO FIGURE THIS OUT! If you want to learn, I am happy to come show you. I don’t have to explain why getting a stethoscope into water pump territory on a running 4.0 is incredibly dangerous.
      And as mentioned previously, we still don’t have an explanation for why 4 cylinders were getting significant coolant from the head for several hundred miles at least. Without clear symptoms (which David may or may not have seen or ignored because they were subtle) the only way that ever would have been found is by pulling the head. Even if there was some measurable coolant loss, it almost certainly would have been chalked up to an external leak, not consumption.

      1. I can’t say I’ve ever had to replace a cylinder head on a car that overheated UNDER MY CARE. My vehicles all get new water pumps and refreshed cooling systems basically out of the gate. This black XJ was a vehicle I never really put into my driving rotation; I bought it, struggled to get around to fixing it entirely, and as soon as I thought I had everything fixed, I sod it before really putting any miles on it; that was my fault. Had it been in my rotation, I’d have noticed the issue and promptly taken care of it.

        With that said, as much as I love the 4.0, it’s not in the very upper echelon of reliable engines; especially in the XJ application, it’s not as reliable as the Slant Six, for example. The slant six has a fixed fan that will never fail. The XJ has a fan clutch that can go bad and a crappy little auxiliary electric fan. The slant six’s water pump can be swapped in 10 minutes, the XJ’s is a job, inviting drivers to defer the work. I can’t speak to the slant’s ability to withstand an overheating episode, but the AMC inline-six cannot handle a single significant overheat without requiring a new cylinder head.

        Love the engine, and agree that if you’re on your P’s and Q’s, it will never die. But it’s not a “just throw whatever oil you got in it, fill it with some dirty water, and run it” kind of motor — especially not in the XJ application.

        1. My brother, my father and I all had Chrysler Valiants with slant sixes, my brothers and mine both had persistent overheating problems. This was back in the 70’s in the Land Down Under, my brother’s was about a 62 S series, mine a 67 VC. We tried all sorts of things to try and overcome the issue, including putting them on a dyno, with no success. All of my later Valiants had Hemi sixes with no overheating issues.

          1. Having lived thru the era in the Midwest, Overheating used to be far more common in the ’60s, than the ’70s or later.
            One overlooked thing, was the Big Three started to use coolant recovery bottles, where before the radiator neck line just ran down the side of the radiator and vented when things got hot.
            2nd, People used to be really cheap, and skimped on Antifreeze, and ran just enough to keep from freezing in Winter. That meant they also ran light on the anti-corrosion additives, that were also part of antifreeze.
            So marginal systems were constantly low on fluid, and full of scale, given how hard the water is here.
            I used distilled, which wasn’t as common.

            Back to the Mopars. I also think the Sixes had terribly undersized/narrow 2 core radiators in passenger cars, the fluid fan/clutch fan could fail to move enough air at low road speeds if the clutch unit failed, but this was hard to notice. the blades still turned.
            Some also had unshrouded, fixed blade fans on the low end/entry level cars that didn’t have A/C
            The worst were the ‘High Performance’ flex fans that ‘saved’ you HP by flattening out at speed

            So anytime I had a Mopar, I would put the bigger V8 radiator on, and add the shroud and clutch fan, along with the coolant recovery bottle
            No more worries about heat

        2. I mean, much like any long lived engine, the AMC straight six dab plenty of years to watch out for. TUPI heads, greased, but not oiled by the engine distributor shafts, But certainly the known water pump failures, which can be quite sudden, can lead to overeating pretty quicky. Stil the motor is easy to work on, the parts used to be relatively cheap, but the best part for a jeep at least is the low end torque which is pretty useful offroad.

        3. I could give you a 50 page explanation of every single thing the supposed ‘Jeep experts’ out there are 150% full of shit on. Minimum.

          I mean let’s see. Just off the top of my head:
          – Head and crank bolts are absolutely not reusable, and never have been, period.
          – That is too much RTV, and that is not enough RTV on bolt #11. Read the FSM.
          – Giving a 232/242/258 more fuel is always the wrong answer. ALWAYS. No exceptions.
          – Your hot air intake/snorkel/etc. is actively damaging the engine, dipshits.
          – No, you absolutely do not replace your air filter often enough.
          – Yes, idiots, the CCV and PCV systems both require active maintenance which you ignore.
          – ‘Just converting’ from HOAT to glycol is absolutely the wrong way to do it.

          The AMC straight 6 is an extremely counter-intuitive engine which has a cult of ignorance that worships it. When taken care of correctly, it will basically go forever, so long as you keep it within tolerances. When you go outside of tolerances on heavily worn or abused parts, all bets are off. (People claiming they don’t on Honda/Toyota/etc. are just as full of shit. Ask any Toyota owner who’s been told a quart burned every 1k is ‘totally normal.’)

          And when the engine has been maintained according the advice of a cult of ignorance, guess what? Yep. That’s heaping abuse and misuse onto it, erasing any margin, and guaranteeing minor issues become catastrophic. Follow the correct care and feeding, and the only thing 4.0’s eat is garbage quality water pumps (I’ve honestly never found a not shit one,) CCV and PCV parts (less than $20,) coolant (needs a MUCH more aggressive flush schedule due to Coolange(SM) Sluj(R) buildup,) and air filters. Sometimes the occasional injector or IAC.

          And before you say there isn’t a cult of ignorance, consider this fact: the 4.0 has a larger throttle body than a GM 5.7 TPI with MAF.
          A larger or higher velocity throttle body will produce an immediate increase in power without additional fuel trim.
          Put more simply: these engines demand a great deal of air, and hate fuel. They’re literally the only engine that could pass emissions through the 2000’s without an EGR. That’s no small thing.

          1. And since I’m sure the next question will be “since you’re such an expert,” here’s how you should maintain a 4.0 for maximum lifespan:

            – Oil change interval should not exceed 5,000 miles or 12 months based on occasional use
            – Jeeps are fairly hard on oil, but Fram Extra Guard is perfectly fine. So is NAPA Gold (Wix,) Motorcraft, Baldwin, AC Delco, Purolator. Just use quality parts and replace regularly. If you off-road or tow regularly, use a larger filter – Motorcraft FL-1A or Mann W9404 is the go-to there.
            – Use only paper air filters, ABSOLUTELY NO OILED FILTERS EVER. I personally recommend Mann, STP red paper; for lots of off-roading, Baldwin PA2163
            – Inspect the throttle body and IAC for debris every oil change (it’s one screw. No whining.)
            – For glycol coolant engines, drain and perform a chemical flush with Mopar 04856977AC every 4 years or ~36,000 miles. Glycol coolants have been re-engineered to be more aluminum friendly, which makes them less friendly to all cast-iron, resulting in more Sluj(R).
            – For glycol coolant engines, avoid “long life” (10yr/300k) advertised coolants. Stick to older formulations with 5 year life. Zerex or Mopar only. Everyone else adds undisclosed chemicals which can cause very bad reactions.
            – For HOAT coolant engines, honestly, just stick with HOAT. There’s nothing wrong with it. Drain, light chemical flush (non-foaming,) refill every 5 years or 50,000 miles.
            – For HOAT (orange) coolant engines, NEVER JUST CONVERT TO GLYCOL. This will completely Sluj(R) the system and kill it. Multiple Mopar 04856977AC flushes, run on water for a while, then another flush.
            – For HOAT coolant engines, you absolutely must not mix or change without aggressive chemical flushing. That includes mixing with any other OAT or glycol.
            – For HOAT coolant engines, Mopar HOAT or Zerex G-05 is the only one you should use (it’s dyed Ford amber.) ONLY Zerex or Mopar HOAT – NOBODY ELSE! Everyone else adds chemicals not disclosed on the label which will cause problems, especially if mixed.
            – NEVER use coolant additives (i.e. Water Wetter, AMSOIL DOMINATOR, Mishimoto Liquid Chill, etc.) They’re all liquid poison for the coolant system. The ONLY safe additive is Motorcraft VC-12 and ONLY on HOAT coolant.
            – For CCV engines, inspect the CCV grommet and lines for cracks every oil change.
            – For CCV engines, disconnect the line and flush the CCV orifice (valve cover) with Brake Cleaner or similar every other oil change (before draining oil!!)
            – For CCV engines, replace the CCV hose every 10 years or 100,000 miles
            – For PCV engines, inspect the PCV line for cracks and looseness every oil change
            – For PCV engines, replace the PCV valve (it’s $5) every 3rd oil change or immediately upon noticing wet oil in the PCV line
            – Monitor aggressively for air in the coolant system; even that often isn’t enough. I recommend quick bleeding the system at the valve and topping off once a year as a preventative. Cavitation is extremely fatal to the meh water pump you’ll be stuck with.
            – Unless you are planning to replace your radiator, DON’T TOUCH THE PETCOCK. That stupid thing always plugs or breaks. Just pull both hoses and flush aggressively with a hose from both top and bottom.

            Sounds like a lot, doesn’t it? It’s not. All that work adds a total of about 10 minutes to a routine oil change. Well, unless you find a problem other than the air filter or PCV. Changing the CCV orifice is… an adventure, let’s say. That’s why I recommend hitting it with Brake Clean every oil change – an ounce of prevention. If it’s cracked or plugged up, it has to be done immediately either way. (I really don’t like the CCV setup, but it does have zero moving parts to break, so there’s that.)
            The key thing is that everything in the intake tract must be as free-flowing as possible AND as clean as possible. Because everything in there doesn’t just go into the intake, it also can get into the oil via the CCV. And any unburnt hydrocarbons are dumped; there is no recirculation. So if you smell unburnt fuel at the tailpipe? You have a major problem already.

            It’s basically unavoidable that the rear main goes every ~100k because of the design. It’s constantly being rotated against. It just wears away the RTV and rubber over time. It’s a wear part by design. Just like every other split rear-main (such as you find on the Slant 6, which also has rear main leaks over time.)

    2. They truly are great engines. My family has had four of them and they’ve never died all with well over 200,000 miles on them. They aren’t engines that you can just ignore however. Ironically my mom was probably the roughest on her 4 L because she would do things like fill her Cherokee full of railroad ties until it was riding the bump stops so that she could work on her garden. But otherwise, we just kept coolant and oil for and they never let us down. The main seals would go from time to time but even with that I just ran and ran.

      They aren’t in the class of engine that seems to be vampire like and it’s ability to keep running. In that class of engine I would put the 318 in the slant six. I had an old ZJ with the 318 and about 11 years in the radiator rotted out. I was driving, towing my boat, and watching the temperature rise. I called my buddy who is my mechanic and he freaked out. “Pull over immediately!“. He then paused and said “wait, you’ve got the 318? Oh, OK. Just drive slow, turn on the heat, and get it in to me on Monday.“ The car was fine and ran like a top until it finally just rusted out.

      1. “They truly are great engines…. The main seals would go from time to time but even with that I just ran and ran.”

        See, you’re doing it too. Maybe I put too much importance on ease of maintenance leading to longevity, but in my opinion, changing main seals is a big enough pain in the ass that I don’t want to have to do it during the normal service life expectancy of the engine. The only one I’ve had to do that wasn’t part of a full rebuild was in a Ford 360 FE big block, which was infamous for being a leaky, not-great engine.

        On the other hand, the humble 2GR-FE V6 in my RAV-4, while not inciting any passion or romance in anyone, just keeps doing its job and never breaking or leaking anywhere. It’s closing in on 180,000 miles, which is no huge deal, and I’m occasionally replacing wear parts not because they’re actually worn or failing, but just because I’m somewhat appalled I’ve let the mileage creep up so high on them. It’s still on the original water and oil pumps and timing set, which is uncharacteristically irresponsible of me, but it literally still runs like new. The compression is still like new. It’s the most uncomplaining, drama-free car I’ve ever had, and since it goes to my kid next year I’m replacing all those wear parts this summer, but dang… that’s what I call a great engine.

    3. Let me start with the fact that throughout my life I’ve owned 7 Alfas (from 1970 GTV to 1991 164) a couple FIATs and a Lancia. I just listed the italian cars, since they seem to be called out the most for being unreliable around these parts. Some of them I bought from people who didn’t concern themselves with things like “maintenance”, yet somehow I’ve never had to replace heads, rebuild the engines or get stranded by any of them.

      ..and then I get to see people call the 4.0 AMC “bulletproof” while at the same time stating “I’ve replaced so many 4.0-liter Jeep cylinder heads over the years”.

      I’m utterly convinced now that “bulletproof” must mean something else.. -_-

      1. Yeah. Over then years have owned at least 11 Alfas not counting projects (most pre 1968 except 2x 164s, 1991 & 1994), two FIATs (73 124 Spyder, 2013 Abarth 500c), sadly 0 Lancias (but not for wanting) — I’ve probably been stranded one time or another by all of them, but it wasn’t EVER because the engine exploded; On the 164s, by far the most troublesome components were the german bosch-sourced relays and switchgears. Got well over 250K on both 164s.
        But I’ve also been stranded by Japanese, American and German cars I’ve owned. Toyota & Merc both needed head gaskets well before their time despite being meticulously maintained. ¯\_(ツ)_/¯

      2. I do wonder about this a lot. There is a curious phenomenon where partisans, er, car guys will tell anyone who will listen that all cars from x company or y country are unreliable money pits before launching into an unironic whinge session about some apparently freak costly failure on their marque of choice.

        Maybe I’m just defensive because I’ve owned a series of trouble-free VWs and have been hearing all my life that they’re basket cases as a rule. That said, the only non-VW I’ve owned was an old-but-low-miles Volvo wagon that I expected to run forever but was beset with gremlins both mechanical and electrical for the few years I had it until it crapped the bed at ~13 years and 105k miles

      3. Heavy enough to stop a supersonic lump of copper jacketed lead?

        I don’t like calling engines bulletproof, I prefer to look at them as understressed, lazy, and with hefty enough internals to be capable of coninuing to run most of the time with issues that often come from poor maintenance and/or age. For example I love my old 460, it’s now over 30 and leaks from the oil pan gasket due to age, but I trust it to drive me across the country if I want to. My little brother’s FIAT with the Lampredi 4 banger, much more fun but I don’t trust it any farther than I can throw it just because it’s too high strung for the inconsistancies in his ability to maintain it properly, and that’s not a slight against him, its an artifact of him just learning to care for a classic car on his own.

    4. IMO, The Jeep 4.0 engines are average at best. They are not any worse than any other engine, but definitely not any particular outlier in terms of reliability. Their reputation for being “bullet proof” seems to be because some guy on the internet said it one day.

      The 4.0 has had tons of very common issues throughout its history. Exhaust manifold cracking problems, fuel rail boiling problems, head-cracking issues, piston skirt cracking problems, persistent valve cover leaks, valvetrain/misfire issues, and more.

      1. I have had several 4.0L Jeeps and nary a problem, even into the 250k+ mile range. For a 1960s-designed engine to last well into 250K+ miles is unusual to say the least. Sure, we expect it in today’s cars. But for its time, the 4.0 was an astounding engine with a great service record compared to many of its peers. Maybe not as “bullet proof” as claimed, but certainly better than many others. The testament to that is how many you still see on the road.

  4. So I’m curious…you pulled this head off the engine intended for your overlanding project right? So at some point you will need to obtain another 4.0 head? Or are you salvaging another one you already had laying around?

    1. I thought he had a bunch of these engines lying around. I’d have just swapped engines with a known good unit (with new water pump etc) and fixed this one later.

    2. No, this was just a spare motor from GREEP. It ran well, so I figured; “Why junk it with the Green ZJ?” Seemed wasteful.

      My overlanding rig has a motor in it. No clue what shape it’s in, though!

  5. Wow. Most people sell as is to protect themselves from shady buyers or (ignorant car owners) that intentionally get free rebuilds or engines.
    I’ve had engines overheat before. I just kill it, park, and find out why. Never needed to replace a head gasket or cylinder.
    Sounds like she drove it HOT and this happened.

  6. Hello, I’ve got one question with the valves breakin, shouldn’t it be done by an alternating movement? Doing it with a drill seems line a good way to not have a regular contact, am i wrong? Though i understand doing it with your stick like some caveman trying to make fire is boring. Keep up, and i have one rule for wrenching, if you keep on working past the sun set, nothing good ever happen, go to sleep and finish in the morning.

    1. I still have my G’pa’s old reciprocating valve grinder (I’m 75) so this tool is well over 100 years old. It still works and makes a rather pleasant whirring sound when the handle is turned. I would post a picture but; well we don’t do that here yet. Happy lapping!

  7. Update: I don’t think he made it. It was still overheating this afternoon and DT thinks it might need a new motor. Please send him kind thoughts for his Sisyphean suffering. I’m sure he’ll give us the deets soon.

  8. I’ve been a British car mechanic and a hotrodder most of my life, too bad you don’t live near me in South Central PA; I have a totalled TJ I believe it’s called with a HO engine and transmission and a 4.0 Cherokee engine with a perfect head (threw a rod) and an entire black black 2007 Cherokee with a great running gear that is holding blacked lights and a new lift kit…and they all need to find a new home. They’re taking up space here and I have 2 british hotrods to put together. Alas. You have my sympathies. Let me know if I can help you with anything.

  9. Nice work! However, you really are making things unnecessarily hard on yourself. It’s taken a long time for me to learn this lesson: sometimes you need to delegate. Just because you CAN do a job, it doesn’t mean that you SHOULD do it. What am I talking about? The replacement cylinder head. When you had the head at the machine shop for a resurface and a look-over, you should have tasked them with a valve grind and stem seal replacement. Sure, it would have cost an extra couple hundred bucks, but then you would have had a head that was ready to go with no additional putzing around. I say this as a guy who is 53 years old and still works on needlessly complicated repair projects now and then.

  10. Not sure why a good percentage of the commenters sound butthurt about this. Allow me to clarify the following for you folks:

    1.) Shit happens. I could see Tracygate happening to me or anyone really. The difference is your average seller would lose the buyer’s number after they go down the road.

    2.) Even if he’s cutting it close, David is going to deliver on his promise. As a fellow procrastinator, there’s nothing as exciting or energizing as near-impossible odds and a deadline set in stone

    3.) He’s not whining. He’s openly owning up to having dropped the ball on this, explaining his process, and giving us sweet content to read to boot.

    Have some empathy, folks. Not everyone was born with the genetic predisposition to start a retirement fund at age 12, obtain a paid mortgage at 29, and a curate a walk in closet full of big-boy pants, pressed and laid out by day of the week. Although you’re entitled to your opinions, and you don’t have to agree with David’s methods, you don’t have to be jerks about it. Stuff like this is what makes him who he is and, in my opinion, fun to read. The kid in me needs a break from responsibility now and then.


  11. A couple bulletproof engines in my arsenal. A 1999 Ford 4.6 made it to nearly 500k untill a computer issue let it over rev multiple times untill it developed a light rid knock… ( Pulled still running ) 2003 Ford V10… Magical motor still works perfectly at 225k as it did new, no leaks, no bad sounds just needs a tensioner pulley ( not the engines fault) A 1985 Chevy 305… Lived it’s live in a C10 untill wrecked at 250k now going into a 78 Chevy Ramp truck to live out it’s days chugging around carrying cars back from the woods.

  12. Stop being such a drama queen and get the job started already! Get the head in and torque’d tonight then go to bed. That’s enough work for an evening, and the rest can be done by mid afternoon tomorrow. Ready for a test run. Good luck, this is a fun job.

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