I feel I've done enough to make a post on this subreddit. This post contains a little over 5,000 words and there will be no TL;DR. I've never laid all of this out in one go before and I'm not using AI even to help me organize my thoughts, so you're getting some grade-A certified genuine grassfed free range humanmade mind vomit with this one.

About 2 years ago this 258/4spd Eagle with 74k miles on it followed me home from Eastern WA, where it had been parked in a field for 20+ years. It was purchased to be a wife's winter driver, her hip went out, and that was it. I got it running, but engine problems were revealed during the revival. Parts sourcing proved to be a giant pain, as AMC made a bunch of changes to their engines and drivetrains in the early 80's, making already spotty documentation even spottier. I probably could have powered through, but I was getting burnt out. I liked AMC I6's (still do) but to be perfectly honest they don't exactly tickle my pickle anymore. Very pedestrian and hum-ho, perfect as a driver in something you want to get in and fast travel to your destination, but for me, not a passion project. And carburetors... Cool in theory, IMO fundamentally incompatible with modern fuel and parts support environment.

Well, I've always wanted something rough around the edges with classic muscle car aesthetic and sound, but as I've gotten older I also want something year-round and fuel efficient, so I decided to undertake my first "real" car project--something more than tinkering and gasket replacements on something that has always felt like "someone else's product", rather than my own vision. I have an extremely limited budget and am prone to discouragement, so you might imagine how daunting this dream felt to accomplish.

About two years later, I'm at the point where the car moves and stops under its own power again, and looks much closer to how I want it. This has indeed felt like a herculean task, from planning, to layout, to execution, with all the changes of plan inbetween, but I'm proud of what I've accomplished so far--all told, the car is probably about 60-70% "done", with done meaning roadtrip-worthy. Here's where all the reading starts!

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The car is now powered by a naturally aspirated 6.5 Detroit, specifically a 2001+ "Optimizer", found only in postdated HMMWV's or step vans, or purchased brand new. Optimizers are the best accessible 6.5, as they feature all the fundamental improvements of late-civilian production, but were/are cast by Navistar, featuring improved metallurgy over their predecessors, which had been their fundamental flaw from the start (1982). Today, a brand new Optimizer long block starts at \~$7,500. I traded $100 and a floor jack for this unit, which I pulled from a HMMWV. It originally had a center-mount turbocharger, which I removed for packaging, simplicity, and personal preference. This necessitated swapping the heads (different intake bolt angles for center turbo heads only). The current heads are Promaxx units with diamond precombustion chambers, fed by an early J-code (dual plane) N/A intake manifold and air cleaner from a junkyard 6.2, complete with paint ID markings. Fuel is delivered to 8 Bosch injectors through new injection lines via a rebuilt DB2-4911 mechanical injection pump, timed to the engine by an aftermarket gear drive timing set, replacing the original double roller chain. The traditional elastomeric harmonic balancer has been replaced by a Fluidampr, and a new noseconeless gear reduction starter is installed with ARP bolts and requisite support bracket. Coolant is pushed through a summit universal radiator by a flowkooler v-belt water pump which I tried (and failed) to paint, and will try again when I someday paint the whole engine black. Upper rad hose is a flex adapter hose, I grabbed the lower hose off the wall at NAPA and trimmed it to fit. A late-90's 6.5 oil cooler has been mounted behind the front skid plate and connected to the engine via hydraulic hoses. The only external belt-driven accessory is an aftermarket 1wire mini alternator, and the only engine components which require electricity of any kind are the starter, glow plugs, and shutoff solenoid. I expect this engine to output about 160-170 peak horsepower, with 250-300 ft.lbs of torque on tap at about 1800rpm.

In order to fit in the car, the front wall of the oil pan sump had to be moved rearward by about 2", and the dipstick relocated to the passenger side. The engine crossmember was heavily modified to clear the engine, as well as to mount the differential (Originally bolted to the engine from the factory. Yes.) and accept a Mustang II rack & pinion unit with custom extended inner tie rods, replacing the zillion bushings and halving the weight of the stock saginaw box steering assembly. The throttle cable is from a mid-late 90's Chevy pickup w/ a 6.5, and just happened to have the correct length and pedal attachment. The oil fill has been moved from the timing cover to the driver's side valve cover, and the CDR system (basically PCV for diesels) has been modified so the hose leading to the driver's side is routed underneath the intake manifold, all to make it look a little more like a conventional V8 of the era. I relocated 2 stock Eagle battery trays to the rear of the car, and connected 2 Eagle batteries in parallel via 1/0 gauge welding cable.

In

The fuel lift/supply system itself is relatively standard for a car of this vintage. I'm using a helper electric pump during the testing phase, but eventually the sole fuel lift pump will be a standard camshaft-driven mechanical diaphragm pump, externally identical to traditional Gen 1 Chevy fuel pumps. The chassis fuel supply hardline has been upgraded from 5/16" to 3/8" using nicopp line. The primary fuel filter/water separator (pre-liftpump) is a knockoff Racor 500FG housing (30 micron), and the secondary filter (post-liftpump) is the factory 7-micron unit bolted to the backside of the intake. I also had to make both pre- and post- secondary filter hardlines.

Engine power is routed through an NSG370 6spd manual transmission from an '05-06 Jeep Wrangler, adapted to the engine by a now-discontinued GM-to-AMC pattern adapter plate, and mounted to the chassis via stock 370 mount and a modified stock crossmember. The 370's closer gear splits and lower ratios at both top and bottom end compared to the AX15 were desirable to me, and its max factory-rated torque figures (272 ft.lbs) were close enough to my engine torque estimates. If this transmission blows, I'll replace it with an AX-15. If not, I plan on picking up a synchro upgrade kit and improved shifter tower for it at some point. The clutch kit itself is for 6.2's and 6.5's, and is physically interchangeable with standard GM clutches of the period (same bolt pattern + dimensions), but contains an extra set of springs to dampen diesel harshness. Spline count and size is the same as for the transmission. I used an extended pilot bushing and a Novak Adapters AX15/370 throwout bearing extended + locked to its maximum depth, to account for some of the adapter plate thickness. The slave Cylinder is also a Novak AX15 unit (longer travel), with the adjustable pushrod set nearly to max extension. The master cylinder is an integrated-reservoir Wilwood unit through the redrilled firewall. IIRC, master and slave cylinders are both .75" bore. The pedal effort feels moderate and requires nearly its full travel to disengage, which is probably about right(?). I'm not sure. It feels okay, but the slave cylinder has begun to exhibit a periodic squeak which goes away when pushing the clutch pedal, so will be tweaking the pushrod more in the near future.

From there, power is split (for now) by an NP231 transfer case clocked down by 15-30 (can't remember which) degrees by a clocking ring adapter. The rear output yoke uses a slip yoke eliminator, and both front and rear driveshafts have been lengthened a small amount for two reasons: The distance between the NP231's front and rear output yokes is shorter than the stock NP119, and the drivetrain itself has been raised by several inches. This car WILL be proper AWD someday, but I overestimated how much room I'd have under the drivetrain tunnel, and this SYE'd 231 came up in the right place, at the right time, at the right price, solving that problem for now. It's smaller, lighter, simpler, and stronger than any stock Eagle transfer case, so it's a fine placeholder while I get the rest of the car ironed out.

The front axle is a stock cut-down Dana 30, which is considered full floating due to its IFS nature. Regardless of its supposedly surprising amount of strength, the CV shafts aren't so sure. This is one of the key reasons I'm committed to keeping this engine at stock power output, as I have no desire or intention to replace the front axle with anything else, nor do I intend to solid axle swap this car--I want it to ride at car height with car feel, I already have an XJ Cherokee, and I don't need a second one. Oh, and I swapped the fill plug for an internal square and ground it nearly-flush with the diff cover for clearance against the crossmember.

The rear axle is a bone stock AMC 15, the direct predecessor to the Dana 35. These are even worse than a D35 and have two-piece axle shafts which are generally vulnerable even to stock 258 torque, so I'm obviously not confident in it were I want to do anything more than forest service trails, which... Might not even happen, so, it's fine for now. Another dislike is its narrow width, which is why the car now sits on 1" spacers in the back. To resolve all of this at once, I picked up a 29-spline Chrysler 8.25 from a Jeep Liberty. Much stronger, 2" wider in total, and with disc brakes to boot. When it gets refurbished and installed will be determined by when I get around to it, or when the AMC 15 dies.

The wheels are a set of powdercoated Eagle steelies donated from an older project, wrapped in some aging BFG's. The steering is, as mentioned, a 20:1 manual steering rack from a Mustang II. The inner tie rods have been lengthened by \~3", and the steering knuckles were reamed slightly to accept stock MII tie rod ends on the bottom side, as opposed to the top (stock). The steering shaft is comprised of 3 sections (column shaft, intermediate shaft, rack input) connected by 1 double u-joint and 1 single u-joint, all stabilized by a heim joint. just after the double joint. Steering feel is moderate and direct. I haven't been able to test for bump steer at speed yet (I assume driving over rocks at low speed should cause feedback regardless) but if necessary, I have another set of steering knuckles to try top-mounted tie rod ends in conjunction with rack offset bushings, or any combination of tweaks.

Appearances are an important aspect of the project to me. I've always liked Eagles mechanically, but they are aesthetically stodgy in my opinion, which is funny, because the style I DO like is even older. Be that as it may, Eagles kind of look a little like a spider squinting at you, and the grille is strangely narrow. Well, I also happen to own a 1970 AMC Hornet (now just a shell, long and humiliating story), which from the A pillar back is the genesis of what would eventually become the Eagle. (AMC Smallbody lineage is Hornet [-> Gremlin] -> Concord [-> Spirit] -> Eagle, all structurally derived from the previous, making for 18 years of the same core unibody structure) The 70-72 Hornet are really handsome little cars in my opinion, however they only featured an aluminum grille setup for 1 year until it was changed to plastic. While mine was missing the headlight surrounds, it still had the grille, which I installed on the Eagle and trimmed to clear the hood latch. The Hornet's headlight buckets were also donated, and to complete the full-circumference chrome treatment, I cut the outer edges off of the Eagle's original headlight assemblies and self-tappered them on. The eventual goal is to find someone to design and 3d print the headlight bucket trim internals, which would complete the look. The holes in the bumper are for radiator airflow, inspired by the way GM did it in diesel GMT400's--but I also love the functional look. Vertical location and dimensions were determined by distance between horizontal bumper ribbing, while horizontal was between the bumperettes I added, and the license plate. And yeah, the yellow plate will be hung on the wall once the car is on the road with valid plates. I removed all plastic body cladding, welded up the resultant trim clip holes (except the real big ones in the back), fabricated bumper end caps for all four corners, then painted the lower body what I hoped would be a plain dark brown. Turns out the lighting that day wasn't good to judge paint hue by, and it turned out to be a sort of reddish-brown. I'll redo it someday.

The interior is pretty tragic right now. The carpet turned out to be pretty fragile, and the dash looks solid but is as brittle as you'd expect for being parked in the desert for so long. However, that makes it a perfect candidate for modding. I cut out the original eagle gauge cluster, replaced it with one I bought for the Hornet ages ago, swapped over the light + wiper switches, and plugged in the backlighting. The batteries are mounted to factory Eagle trays behind the front seats, making this a 2-seater, as opposed to what was practically a 2+2 to begin with, so not a huge loss. I deleted the cable mirror adjusters and cut apart a pair of off-the-shelf mirrors, glued the Eagle mirror lenses to that adjustment mechanism, then screwed all of that into the Eagle housings, making for basic manual-adjust side mirrors. The drivetrain tunnel currently amounts to a giant gaping exhaust fumigation hole, to be patched later. There's no T-case shifter right now, so the car is shifted into/out of 4x4 from underneath with a crescent wrench. Interior and exterior lighting all works, as does the radio, though the front speakers are dead. The rears are fine. Oh, and I've also replaced both door handles, the igniton lock cylinder, and all the exterior locks (I lost the original keys.)

So that's about it for now. I don't yet trust it enough to so much as drive to the mailbox just yet, but I have taken it around the driveway about 8 times now, up through 2nd gear, and given it some good throttle over the rocks. It vibrates a lot (these engine mounts aren't super dynamic) but otherwise just kind of works right now.

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What's left to do, then? Uhhhhhhhhhhhhhhhhhhhh

I need to make a new front crossmember. This is my first fab project, and I included a lot of adjustment in this first design, but not quite enough for me to feel comfortable kludging in any more tweaks. The engine needs to be lifted and moved to the passenger side by about 1/2" in each direction in order to both provide better steering shaft clearance from the rearmost driver's side injector, AND provide exhaust clearance from the steering shaft. The engine currently has no manifolds on it because they'oun't'fit. Moving the engine by that much would allow me to raise the front axle by another 1", putting it back at stock height, which would necessitate moving the steering rack up as well, and possibly even grinding a little clearance into the cover/diff housing. I'd also like to use a different, more compact and confidence-inspiring engine mount setup than the biscuit mounts I used this time around, and I believe I've come up with a generally more satisfactory and elegant mounting solution for all components involved. For needing to remake such a critical component, I'm viewing it as an opportunity for improvement using all I've learned.

I also need to make a new oil pan! Because of the lost sump volume, I decided to extend the sump to the passenger side to make up for it. This is fine in theory, but it roughly triples the amount of welding required due to all the sectioning, which invites an order of magnitude more opportunity for error. My first pan attempt warped too badly to be installed, and my second attempt had vastly superior welding yet still sprung a leak that escaped leak testing, presumably waiting until I actually installed it on the engine and it was tweaked just right, or maybe it was revealed by engine vibration/heat cycles. Furthermore, I unfortunately didn't account for the starter bolts when making the pans, meaning in order to fully unbolt the starter, the wide-sump pan (which extends under the starter) would need to be dropped first. To sum up, I've determined that I'm okay with losing \~1qt in the sump, so V3 will be a single wall relocation.

The eventual exhaust will be a set of custom blockhugger headers which route out of the front wheel wells, back under the kick panels, through the longest existing cherry bombs, and side dumping ahead of the rear wheels.

Glow plugs need their own pushbutton ground-switched relay harness, and I need to finalize verifying the fueling solely off of the mechanical pump. I'm thinking about adding an alternate/cutout fuel path which includes the electric pump for emergencies, but generally, my principles demand I minimize the electronics in this car wherever I don't actively want to experience them (i.e. good sound system).

The entire front suspension needs new bushings. I'm committed to doing this after I have the drivetrain how I want it, because suspension bushings are for some reason more daunting to me than modifying the car's structure. All the pressing in, pressing out, maybe burning or cutting stuff out, any nick becomes a problem... Yuck.

The interior will eventually receive the aforementioned tunnel cover plate, sound deadening, a new carpet, and a respectable sound system. Speedometer still needs to be connected, it will 100% be way off. This engine also has a cable tachometer output, and I bought a cable tach to match, just need to have a cable made. I might swap out the steering wheel for a 67-72 Chevy truck unit, which are 17 1/2" vs the stock 15". Ideally I'd find something wood rimmed, but finding an affordable one of a large size is like finding hen's teeth. Also, CB Radio? Mobile amateur radio? One of the two. After the tunnel pan goes on, the rally gauge package will go in with 4 relevant gauges--probably coolant, oil pressure, fuel lift pressure and voltage. Oh yeah, and I need to finish up my e brake handle swap, which is about halfway done so far.

Upgrading to Hella H4 projector housings, which will require a proper standalone headlight circuit. I hate crappy stock relayless headlight wiring.

Different steel wheels of identical dimension, but which accept dog dish hubcaps. Without dog dishes this project is doomed and my entire life is ruined.

Repainting the bottom part of the car.

All kinds of weatherstripping.

Since the car has no A/C and I don't desire or plan on adding it, I'm committed to using this car as a future testbed for passive thermal management for these increasingly hot years of ours. All windows will receive crystalline film, I'll source louvers for the rear windows, I'll install an evaporative cooler plumbed into the cowl ducting, and I'm extremely interested in experimenting with a "safari roof" using strategically applied black + white paint. To describe it briefly: Using a cut-off roof skin from another SX/4 or Spirit, the new roof skin will be separated from the original roof surface by \~1/2", providing an airflow layer between the layers which will be utilized particularly at speed. The top (exposed) surface of the new skin will be painted with rubberized white tin roof paint, reflecting incoming UV, while the perpetually shaded area of the original roof skin will be painted black, radiating interior heat into the airflow layer under the skin to be carried off while driving. I'm not yet sure how the skin will be attached, as that's frankly ages in the future, but I'm sure I'll figure something out. Maybe I could extend it over the windshield as both sun visor and air scoop? Anyway, Land Rovers had a safari roof option back in the day, my unique twist on it is my intuition of using paint to help prevent heat accumulation while encouraging interior heat dissipation.

Once the car is driving for real, I'm hoping to make 25+MPG on pump diesel. The ultimate goal is to fuel it using a blend of waste motor oil, transmission fluid, gear oil, diesel, and pump gasoline as a thinning agent, all settled and filtered appropriately of course, which could improve efficiency even further. If all of that is achieved, I should have a roughly 600-mile road trip range (same tank capacity goes further) at prices nearing free. This car would do just fine hauling a little trailer to go pick up parts, spare engines, transmissions, go see places, do things, car meets, whatever, at any time of year, in any weather, and confuse everyone everywhere while doing so. That's the dream.

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A few asides here. As you might have wondered, "how heavy is that engine". 6.2/6.5's are usually estimated at 700-750lbs depending on accessories. The stock lightened (post '80) 258 is 450-500 considered similarly. One goal of the project is to do nothing to the front suspension, and so a number of the measures you read about are an attempt to make that work. Belt driven accessory deletion, mini alternator, steering swap, battery relocation, I didn't actually weigh anything specifically but the car seems to ride at a normal height and feels normal to jump around on the bumper of like we normal humans do frequently, yes.

Secondly, fun fact, the HMMWV was designed under the final years of AMC's ownership of AM General, and featured cut down AMC 20 axles until the early 2000's, but of course old units are still driving around with them today. The 6.2/6.5 don't have an AMC connection, but the HMMWV does, so the fact that this engine is from one feels fitting.

Now, a bit of a love letter to the 6.2/6.5 themselves. These are perhaps the most misapplied and therefore misunderstood engines ever produced, and as usual it's GM's fault. To begin this little excursion we will look at the timelines. Oldsmobile released the 5.7 v8 diesel in 1978, and GM decided in their infinite wisdom that their new diesel they were selling to millions of americans was invulnerable to water in the fuel, which all diesel had back then because fuel storage was crap. Diesel injection systems use fuel as a lubricant, and water is not a lubricant. Furthermore, the 5.7's head bolts were admittedly marginal, and what does water do in a combustion chamber? It increases combustion pressure. This single screwup trashed tens of thousands of fuel systems and blew tens of thousands of head gaskets, almost singlehandedly ruining Americans' perceptions of domestic diesel passenger cars, particularly GM's offerings, and to a lesser extent diesel cars as a whole. They were low on power, smelly, a little smokey, sounded like a box of rocks, didn't want to start in the winter, and now you learn they needed injection pumps, injectors, and head gaskets every 2,000 miles??? No thanks. The 5.7 was considered a pretty repugnant engine by the 80's, even though GM introduced water separators and Oldsmobile further improved the engine itself--still no powerhouse, but it no longer blew up in time with its own maintenance intervals.

Along comes the 6.2 in 1982. GM and Detroit had surely been working on this engine throughout the entire 5.7 debacle, and had been watching sales of that engine tank toward the end of development despite having solved their core flaws in previous years. What few people without direct involvement with the 6.2/6.5 know is that they share Gen 1 Chevy mounting dimensions, and certain aforementioned parts similarities with other Gen 1 V8's should the need arise. Yes, this means a 6.2/6.5 will drop into any hole someone could stuff a big block, and with precious few fuel system modifications given its low pressure lift pump. You can even fit them into plenty of SBC-powered vehicles, with the usual conflict being the heater box. But mounts and bellhousing both slot right in, excusing the usual GM motor mount confusion that seemingly exists with any Gen 1 swap. Point is, classic GM parts bin mentality, which IMO is fundamentally a good thing. But there's a bit of a problem going forward. The 6.2 was originally spec'd for a forged crank and pretty good metallurgy (supposedly a high nickel content), and rather late in development, both were axed. Cast crank, subpar metallurgy. Both adequate, but only just.

Trivia--in 1981 (1yr prior to release) GM installs about 1000 6.2's into full size cars, which it loans out to a few government agencies for testing. They do very well, and there are still a tiny handful of these cars floating around that nobody cares about for some reason despite how neat and what-if they are.

So anyway, here's GM holding this universal GM-spec diesel engine that made around 130hp/250 lb.ft at its introduction, an engine that has already tested well in full size cars, and is advertised almost solely as a light duty fuel pincher, and an engine that has been cheapened in a way that will adversely affect it under a cocktail of poor maintenance and heavy workloads. But everyone hates GM's diesel cars, at this point the 5.7 and derived 4.3 are selling poorly and will only last 3 more years. So what does GM do, given these market conditions?

They push the 6.2 up in weight class. No cars, just trucks and above. Loads of half tons, sure, but also three quarter tons... One tons... Humvees? Motorhomes??? Boats??????? Guys, I know you're only commissioning, marketing, and selling these things--not sure if you realize this, but your new engine is competing in numbers with a 305 with an air cleaner lid flip.

So today, these engines have a reputation for problems, and reasonably so. 1 year after their release, they were competing in the same weight class with Ford/International's IDI, which started at \~170hp/305ft.lbs and were generally VERY well built. By 1989, they were also competing with the 12v Cummins while still only making a piddly maximum of 285 ft.lbs in top workhorse spec, where a Cummins can basically be turned up and put into service as a reliable hotshot rig right off the lot. You have an engine probably built for 1/2 ton and SOME 3/4 ton duty competing with what served reliably as actual medium duty truck engines. Many 6.2/6.5's were ridden hard, put away wet, rightfully shit talked when viewed strictly from the perspective of market competition, and as usual, GM kind of screwed up in a whole bunch of ways.

But today, in 2026, we also know all we need to know about the 6.2 and 6.5, and have solutions for all of their flaws even in medium duty usage. In my humble opinion they are spectacular car and 1/2 ton truck engines. If you know what you're looking for you can find good ones for cheap, and they can last as long as any other diesel. You can even use them in heavier stuff if you know what you're doing. Just keep an eye on the harmonic balancer (better yet replace it with a Fluidampr), have your injectors balanced every few years (or do it yourself, it's easy), try not to lug the engine, add lubricity to modern low sulfur pump diesel, and enjoy the V8 noises and excellent fuel economy in your cruiser. There's some guy out there running around in a 6.2 diesel corvette claiming 35+mpg and I believe him given that well-maintained, grandpa-spec stick shift squarebodies are documented as having approached or exceeded 30mpg under the right conditions. That's gotta be as close to having your cake and eating it too as it's possible to be in my book, because these sound just like a big block. Because they kind of are one--the redheaded stepchild of the Gen I V8 family.

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So, yeah. That's all I can think of for now, and I've definitely forgotten some stuff, but that's okay. I'm a subscriber to the Freiburger method of "don't get it perfect, get it running", which will persist indefinitely when it comes to purely aesthetic aspects of the car. The paint will always be a little dingy, there will always be dirt in places I can't reach, but I want the drivetrain to be solid enough that I'd trust it hauling me anywhere, through anything. I can't stop the car from getting a little battle damage on the outside, and frankly this entropic ride that is life demands some level of respect and honor of that lest I go insane. I'll stop rust from becoming a problem, repair/replace unsafe glass, pull dents and touch up faded paint whenever I feel like it, but life's too short to get bent out of shape about it in the meantime. That doesn't mean I don't love or don't care about the car; quite the opposite. I will look at it and see all we've been through together.

Feel free to ask any questions about any aspect of the build, or the engine, or whatever. As I didn't really hint at earlier, I do in fact have a video of it driving around the loop which I'll post soon, but I guess you can't mix pictures and videos here and I can't be bothered to upload and post an entire youtube video about it, so uhhhhhh, subscribe and SMASH that like button for part two on this subreddit, like tomorrow or something maybe.