Home » Lightweight Chrysler Slant Six Vs. Heavy Cummins Diesel: Which Of These RVs Would Last Longer?

Lightweight Chrysler Slant Six Vs. Heavy Cummins Diesel: Which Of These RVs Would Last Longer?

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The Autopian has been sorta-shopping for an RV for quite a while now, and part of the reason we haven’t pulled the trigger is that we’re looking for something special. Something stylish, vintage, reliable, spacious, and most importantly: something with a stickshift. It may come as no surprise to many of you that most RVs are automatic; America gave up driving the stickshift many decades ago. Still, if you look hard enough, you will find manual transmission RVs, and these two that I’m about to show you are the most compelling in my eyes because those standard transmissions are hooked to unkillable motors.

The one thing I care about when it comes to an RV is that it works. I’d rank “removing and rebuilding an RV’s engine or automatic transmission” somewhere between “debate with Tesla YouTubers whether the Model Y is the greatest car of all time” and “rebuild an automatic transmission valve body works” on the list of activities I want to do anytime soon. As such, the only RVs that remotely intrigue me are ones with manual transmissions (which tend to be easier to remove and way easier to rebuild than autos) hooked to unstoppable motors.

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Recently, two RVs have popped up for sale in the LA area, and not only are they both relatively affordable, but they both feature engines known for Never Dying. The first is a smaller RV called the Clark Cortez:

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This is a machine developed by a Michigan-based company named Clark, which is known for its forklifts, and also for pioneering those tractor-like tugs you see at airports. The Cortez motorhome is a compact front-wheel drive cruiser outfitted with a standard 225 cubic-inch Chrysler slant-six mated to Clark’s own four-speed manual transmission. And it’s gated!:

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My colleague Mercedes Streeter has already written the full story of the Clark Cortez, so read that if you have a chance. Here’s a quote describing the vehicle’s basic layout:

According to Clark, 60 percent of the camper’s weight rides on the front axle for handling, traction, and stability. In terms of motorhome equipment, everything that you’d expect to be there is present. It sleeps four adults with a floorplan that includes a full kitchen and bathroom with shower and toilet. The coach’s engine feeds from a 25-gallon fuel tank and there’s storage for 30 gallons of water onboard. The brochure doesn’t note anything about waste capacities.

Brochcort

I’m a huge fan of the Chrysler Slant-Six. I daily-drove a 1965 Plymouth Valiant for an entire winter in Michigan, and I never had any issues with the Leaning Tower of Power, despite me having bought that old rustbucket for just $2 grand. The motor ran like a top!

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If you don’t believe me, give this a watch!:

So I’m already sold on the Clark, even if I know it’s got more weight to carry around. The Cortez weighs 7,000 pounds, or over twice what my Valiant did (it helped that my Valiant had undergone some salt-induced weight reduction).

Anyway, here are some more photos of the Clark from the Facebook listing. The thing needs work — with rust on the roof, insulation missing, and a dashboard that looks like it was submerged in the ocean for a bit — but at $5,800, maybe it’s still an OK deal?

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Still, even if that Cortez isn’t perfect, its trump card is the Chrysler slant-six. It’s a truly unkillable motor, and the prospect of that being hooked to a beefy four-speed built by a company known for its industrial machinery — I like it. You know what else I like, though? Like Clark, it’s a company that starts with a C. It’s also based out of the midwest, and it’s also in the heavy machinery business. I also spent a summer there working as an Advanced Concepts Engineering Mechanical Development intern.

I’m talking about Cummins.

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That’s what you’ll find in this 1971 Grand Coach Crown RV conversion (clearly, this was once a bus). The engine is a Cummins 220 “pancake motor.” It’s mid-mounted, and hooked to a Spicer five-speed (some had Eaton Fuller 10-speeds; the seller on this one says it’s a five-speed) with a huge stick wrapped in a hilariously tubular boot:

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And the living quarters appear to be in decent shape, too:

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What do I know about the Cummins NHHS 220? Not a ton; it’s 12-liters of fury compared to the Clark’s 3.7, and it makes over 600 lb-ft of torque, which is a good thing, because this camper is humongous.

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It’s a fascinating motor — six cylinders sitting on their sides, all mounted in the center of the coach. This big-rig motor is unstoppable according to the commenters on Barn Finds, with HotPotato writing:

The Crown Supercoach is indeed iconic…and not just for the retro-future mega-Twinkie styling which was unchanged for 40+ years. Most school buses are built on medium-duty lowest-bidder beer-truck chassis. Crown built its own chassis, and every mechanical component installed was from the world of 18-wheelers. That’s the reason for the mid engine and the tall floor: there’s literally a semi powertrain under there, cleverly turned sideways to save space. It can be serviced anywhere with standard 18-wheeler parts, and it will outlast any other school bus on the road: a million miles is nothing, and literally the only reason these bad boys were retired after decades of service was because emissions rules required it.

Here’s what commenter Dave Wright had to say::

They moved 80,000 GVW trucks all over the country even before freeways. Geomechs is on the money as usual…….220 Cummins built the prosperity we have today moving 80,000 of whatever wherever we needed it.

And here’s a quote from skoolie.net:

I would guess it’s most likely a Cummins 220 HP (non-turbo). If it runs well it’s a very fine engine and with
a 10 spd. behind it it’s very close to a perfect combination. The NHH-220 specs: 743 cubic inch 220 hp @ 2100 rpm,
606 lbf/ft TQ @ 1600 rpm. The key is that the engine only produces about 600 ft/lbs of torque and the transmission
is built to take 900 ft/lbs and pull 80k lb. trucks all day long. You just can’t stress that transmission enough with that
engine or fully loaded Crown to cause any real heat build up.

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Cummins itself writes about this “Pancake” motor on its website, noting that in 1954 it powered America’s very first diesel school bus:

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The Crown Supercoach was the first diesel-powered school bus, with a Cummins NHH-200 hp horizontal ‘pancake’ engine mounted midship underfloor. The 12.2-liter diesel was ideal for hill-climbing and enabled the chassis to add a third axle, increasing to 91 seat capacity for school districts with growing student populations. Known as the ‘royalty’ of school buses due to exceptional build quality, the 40 ft. long Crown featured 26 roll bars in the roof for added strength and safety.

Clearly, these buses were beasts. But they also weighed at least 20,000 pounds.

So which of these — the lightweight slant-six “Leaning Tower Of Power”-equipped Clark mated to a four-speed or this huge Cummins-powered Crown hooked to a five-speed — do you think would be easier to maintain and last longer?

Topshot: Facebook Marketplace/Cummins/Plumkrazygarage

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Mercedes Streeter
Mercedes Streeter
6 months ago

The Crown Supercoach is a part of the Autopian RV/Bus Expanded Universe, too!

https://www.theautopian.com/this-vintage-crown-bus-has-a-mid-mounted-diesel-engine-a-manual-transmission-and-a-wonderful-interior/

If it were my money, I’d get the Crown. Those old buses were built to last and the conversion looks like it was done professionally. Let Sheryl work her magical cleaning powers and we could sleep in it almost right away.

On the other hand, the Clark was built to be a motorhome from the start. It was also built with an all-steel body for longevity. Unfortunately, this one hasn’t lived the best life. We’d have to gut that roof. Then, there’s the FWD powertrain. This isn’t the Oldsmobile UPP with a Chrysler engine, but a more bespoke setup with parts that’ll be hard to find. Ignoring all of that, the poor engine has a lot of steel to move.

Ramblin' Gamblin' Man
Ramblin' Gamblin' Man
6 months ago

Some useless trivia for you:

The late actor Vincent Price, who was an art lover and collector, owned a Clark Cortez which he used to travel to art auctions and estate sales to buy artwork. It came in really handy for him because he had a bad back and would often retreat to the Cortez for a little wine and a nap! 🙂

After his rest he’d head back to the art auctions buy a bunch of art, and he found that the Cortez was perfect for hauling his newly acquired art work home. His family said that the loved the Cortez, he went everywhere in it on his quest to buy art and had many happy memories with it.

Collegiate Autodidact
Collegiate Autodidact
6 months ago

Ha, knowing what I know about Vincent Price I wouldn’t call that bit of trivia useless… that connection is as good a reason as any to go with the Cortez rather than the bus even if this particular Cortez wasn’t owned by Price.

Ramblin' Gamblin' Man
Ramblin' Gamblin' Man
6 months ago

He was an interesting guy and I learned about his Cortez ownership when I read his Biography that was written by his daughter Victoria.

Ben Lamb
Ben Lamb
6 months ago

Buy the clark and scour copart for a rollover / vandalized wrangler 4xe to do a frame swap.

Paul B
Paul B
6 months ago

The Golden rule of buying a RV:

Never buy one that has had water issues. The water will find its way into to floor and start rotting and mold. You will end up spending a fortune fixing the floor.

Plus there are probably a lot more options for parts for the Crown should the need arise.

Also, many more mobile heavy vehicle mechanics should you get stranded.

Ronald Pottol
Ronald Pottol
6 months ago

Crown. Sure, I’m a former school bus driver who has driven their buses, but, Cortez have some parts availability issues, a dozen years ago, I was thinking about buying one, but that transaxel is unique to the vehicle, good luck with parts, and that goes for suspension bits too. The body is all steel though. Make sure you understand parts availability for your bus, like brake drums.

Slower Louder
Slower Louder
6 months ago

Clark before Crown on grounds of aesthetics and size. Clark reeks of Autopian oddballery. (Reeks in the best possible way. ) The Crown is just too damn big and heavy. Caveat: the interior of either could make a germophobe of the most jaded sewage plant worker.

Canopysaurus
Canopysaurus
6 months ago

Tough call. I cut my driving and wrenching teeth on a Slant Six and they are tough, reliable, and super easy to work on. Plus there must be a billion of them in junkyards by now, so parts should be available forever.

On the other hand, that old Cummins is a super warhorse and who doesn’t like flogging a diesel? These are unbreakable and reliable, too.

Thinking strictly about drivetrain, I do think the 225 will be cheaper to maintain and probably to operate as well. The 220 is fairly old and I can’t speak to parts availability or cost. I have no experience with that Clark 4-speed, but they are an industrial company so, if anything, it should be overbuilt. The Cummins works best with the 10-speed where you can really wring the most out of the motor, especially in hill country, but the five’s probably OK.

Aesthetics? The Crown is gorgeous; the Cortez is interesting. If the rust damage on the Cortez isn’t too serious it should be fine. Sitting up front in a bus is like being the captain on a ship with that panoramic view. The Crown will have that big rig sound, too.

On size, the Cortez is smaller so should be easier to maneuver and park and less thirsty. The Crown will be more comfortable OTR with more interior room and better accommodations. Plus you can cram more merchandise in the Crown for Autopian meets.

If it’s going to be based in CA, the Crown will have to meet some emissions standards or no go. If it’s based outside of CA, it probably won’t matter. On the other hand, is anything named after Cortez welcome in CA?

If it’s my choice, I’d take the Cortez, but I’d want the Crown. Your needs may vary.

Mike Harrell
Mike Harrell
6 months ago

“Something stylish, vintage, reliable, spacious, and most importantly: something with a stickshift.”

Well, since you put it that way:

https://seattle.craigslist.org/sno/rvs/d/camano-island-fire-truck-tiny-home/7736216795.html

Collegiate Autodidact
Collegiate Autodidact
6 months ago
Reply to  Mike Harrell

Pretty cool!! But terrible fenestration…

Last edited 6 months ago by Collegiate Autodidact
JunkerDave
JunkerDave
6 months ago

You think it should be defenestrated?

Collegiate Autodidact
Collegiate Autodidact
6 months ago
Reply to  JunkerDave

Ha. Might be a little tricky to drive it to Prague from Seattle though.

Eggsalad
Eggsalad
6 months ago

I’m not sure where in the wheelbase the “midship” engine is in the Crown, but in a past life I had some experience driving a rear-engined bus with a manual transmission, an American Eagle Model 10. And after 10+ years, a 40′ long shift linkage gets so much slop in it that any idea of a shift pattern is long gone.

Alpine 911
Alpine 911
6 months ago

Bus. Or a Vixen Motorhome

Angrycat Meowmeow
Angrycat Meowmeow
6 months ago

Is that a can of starting fluid on the kitchen table in the Cortez? Get the bus.

notoriousDUG
notoriousDUG
6 months ago

Yeah if they used ether to start it assume damage.

Never use starting fluid.

Alan Christensen
Alan Christensen
6 months ago

Since motorhomes are large boxes of systems about to go bad (electrical, plumbing, HVAC, appliances…), and since old coaches are hazmat-level petri dishes, you want at least a reliable engine.

As for the slant six, the 225 in my family’s ’61 Dodge Lancer drank oil at an alarming rate. A quart per gas fill up. But it kept chugging along.

Jimmy7
Jimmy7
6 months ago

You want an Ultra Van, the Corvair of motor homes. Fiberglass, space framed, rear-engined…it’s practically a race car you can live in!
https://www.macsmotorcitygarage.com/seeing-america-slowly-the-corvair-powered-ultra-van-motor-home/

Geoff Buchholz
Geoff Buchholz
6 months ago

If the choice must be this one — and there’s no third choice like a GMC Motorhome (the correct choice, as many have observed) or, y’know, THE RV LITERALLY SITTING BEHIND TORCH’S HOUSE — then it’s gotta be the Cortez.

The rust is a bummer, but if anyone knows rust and how to beat it, it’s David.

The engine will be easier to fiddle with when necessary, the interior doesn’t look THAT bad, and “Cortez” is probably the coolest RV name of all time.

Sc00t3r
Sc00t3r
6 months ago
Reply to  Geoff Buchholz

Yeah! Why not the one behind Torch’s house? Getting it back roadworthy could be a great Autopian wrench-a-thon!

Ronald Pottol
Ronald Pottol
6 months ago
Reply to  Geoff Buchholz

GMC! It’s a motorhome, of course it has a slush box.

Dead Elvis, Inc.
Dead Elvis, Inc.
6 months ago
Reply to  Geoff Buchholz

“Cortez” is probably the coolest RV name of all time.

Probably not, from the perspective of people with deep roots in what we know as Mexico.

Geoff Buchholz
Geoff Buchholz
6 months ago

You are absolutely right. That should read “cruelest RV name of all time.”

Dan Pritts
Dan Pritts
6 months ago
Reply to  Geoff Buchholz

GMC motorhome all the way.

Defenestrator
Defenestrator
6 months ago
Reply to  Geoff Buchholz

The problem isn’t the rust itself so much as the result. Roof rust plus damaged ceiling insulation makes me think massive water damage from the roof rusting through. Unless it was puddling somewhere, the whole roof might be thinned instead of just a few patches, and the floor beneath it could be trashed and moldy too. It could be a couple patches externally and internally, or it could need basically a full gut along with a whole new roof.

Edit: after a closer look at the listing, good and bad news. It either had a clogged condensation drain or a leak around the air conditioner. So, more patchable but the front seats and console look like they were submerged in water because they basically were. There’s probably a ton of mold around the seats and dash, including in the wood under the rug. Basically the front 6′ or so of the interior needs to be totally gutted and replaced.

Last edited 6 months ago by Defenestrator
Bob Tenney
Bob Tenney
6 months ago

In the unlikely event that there was a crazy person involved, you could have hemi slant-6 shipped over from Australia. Assuming you know a guy.

Cheap Bastard
Cheap Bastard
6 months ago

“literally the only reason these bad boys were retired after decades of service was because emissions rules required it”

So this thing can still pass a smog test?

Alan Christensen
Alan Christensen
6 months ago
Reply to  Cheap Bastard

In CA vehicles built prior to a certain date are exempt.

LX Arlo
LX Arlo
6 months ago

Unless they are over 14,001 GVWR and diesel powered. In which case it will need to pass an annual opacity test/inspection. If she’s running good it should be easy enough to have under 40% opacity.

Last edited 6 months ago by LX Arlo
Ronald Pottol
Ronald Pottol
6 months ago
Reply to  LX Arlo

Yeah, you can tweak a Crown to pass that, barely ????, my school district managed it.

Gilbert Wham
Gilbert Wham
6 months ago

Get the bus. Remove and burn the carpet immediately, but get the bus. The space! The split windshield! The STRIPES!
Bus.
Busbusbusbusbusbusbusbusbusbus.

Stacks
Stacks
6 months ago
Reply to  Gilbert Wham

Bus!

Gilbert Wham
Gilbert Wham
6 months ago
Reply to  Stacks

BUUUUUUUUUS!

86-GL
86-GL
6 months ago

This is for promotional purposes and car shows right? Can you pick neither?

The Cortez looks great and is by far the more reasonable option. I could see a nice Autopian logo looking right at home on the side. Also digging the GM 2500 wheels! That said, are you addicted to rust? Rust on the body and roof is like the one thing even shitty RVs don’t need to worry about, why go into it having to deal with that nightmare?

The bus is obscene and hard to park. Anything that goes wrong with it is heavy wrecker/heavy mechanic time. I don’t care how good these motors are, something will go wrong. There is a reason most school buses and RVs are built on medium duty truck chassis, they may not be the most robust, but they can be serviced by mortals and normal tools. This is one of these things where buying overkill just leads to big problems. You need the budget of a metropolitan transit authority to actually keep a machine like that on the road.

How about a nice Airstream or a Boler 17 towed by a Galpin Ford F150?

Or, if it must drive itself, a polished aluminum Grumman Kurbmaster with a bunk bed and a kitchenette?

Or a GMC motorhome!

https://www.performancetrucks.net/forums/attachments/projects-gallery-189/61468d1332890716-ghetto-van-project-kurbside-van-polished.jpg

Last edited 6 months ago by 86-GL
EmotionalSupportBMW
EmotionalSupportBMW
6 months ago

That Cummins is under less stress then a Buddhist monk on a week-long all-inclusive Cancun vacation. 220’s were a main stay of Maine lobster boat flotilla for near a half century, tell those Swedes showed up. Won’t spin much past the land equivalent of 16 knots. But it will spin on whatever liquid you got, as long as ain’t water. Heating oil, kerosene, Jet A, Jet B, Jet O negative, Allan’s Coffee Brandy.

Arrest-me Red
Arrest-me Red
6 months ago

By the time you are done updating, you could buy a higher end used one. Then think about black tanks and the weight of cargo. Granted they look great.

TheNewt
TheNewt
6 months ago

I think the Cortez is the way to go. It is more interesting visually. There are enough projects in there to provide articles for a long time: David messing with the engine, The Bishop providing input on a re-design and Torch putting together a graphics package featuring the Autopian “A” logo on the sides. Provide some room for reader input as well. Then Mercedes can pull it all together and write about the overall RV project. You could do that with the Crown, but really, the Cortez seems to lend itself to the Autopian astetic. Oh, you can also do an XPEL treatment on it when you’re done too.

Last edited 6 months ago by TheNewt
Urban Runabout
Urban Runabout
6 months ago

Of these two – The Crown Supercoach is the way to go.

But if I really wanted an RV – I’d go pick up the 20 year old 40′ DutchStar that my folks will have up for sale soon after having lived in it full-time since it was new.

MrLM002
MrLM002
6 months ago

Neither. GMC motorhome is the way to go.

86-GL
86-GL
6 months ago
Reply to  MrLM002

The correct answer.

Mark Tucker
Mark Tucker
6 months ago

Tough one. I think the big Crown would be a more useable and road-trip-worthy machine, but that Cortez is just plain cool. And you’re right about the slant six; one of the best motors of its era, and can make quite a lot more power if you want it to. (I’ve heard of drag racers running slant sixes getting 400 horsepower out of them, though probably not long-term-reliable enough for a motorhome.)

Ronald Pottol
Ronald Pottol
6 months ago
Reply to  Mark Tucker

The transaxel is unique, and I believe they have u-joints that can fail at full lock and full power. Parts can be an issue.

Slow Joe Crow
Slow Joe Crow
6 months ago

Tough one, I think the Clark Cortez was a brilliant design, but it is underpowered and rust prone.. Heresy is that it works better with a 318. The Crown Coach is massive but looks well executed.
Go Cortez, you know the Slant six, and it’s easier to park

DialMforMiata
DialMforMiata
6 months ago

Oh God, that “sculptured” wall-to-wall carpet in the Grand Coach is giving me the shivers. That exact same stuff was in my house growing up. I like the look and size of the Cortez much better but that roof rot and the accompanying leaks are worrying. Going with the Cortez, I think that it’s not only going to be more reliable to begin with but it will be much easier and cheaper to fix when it all goes horribly wrong.

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