Each and every Redline Rebuild starts with a plan … and most go off the rails at some point. The original scheme for the Jeep 4.0-liter straight-six gets a revision this week, but, happily, for a good reason.

The whole idea behind the selecting the Jeep was a quick in-and-out rebuild using stock parts. Davin has done plenty of stock rebuilds, and there is nothing wrong with restoring a solid design to factory spec. Well, we all say it’s fine to leave well enough alone, but, given the chance, most of us will take the more fun path. For the Jeep, this approach makes a lot of sense, because Davin can bump up displacement without even opening the aftermarket catalog or ordering custom pieces.

It sounds too good to be true, doesn’t it? Davin thinks so—until he reads that pieces of a Jeep 4.2-liter straight-six’s rotating assembly can be combined with a 30-thousandths of an inch overbore in the 4.0-liter block. Suddenly, Davin has a 4.6-liter engine on his hands.

Of course, it’s not exactly that easy. Davin talks through the exact specifics of why plans like this one must be thought through.

Beyond that shift in plans, there are also a whole bunch of RockAuto boxes to open in this episode. With fresh parts gleaming on the shop table, it is not long before the paint is dry on the block and assembly begins.

If you are curious how the final product will behave, be sure to subscribe to the Hagerty YouTube channel to never miss an update.

Thanks to our sponsor RockAuto.com, an auto parts retailer founded in 1999 by automotive engineers with two goals: Liberate information hidden behind the auto parts store counter (by listing all available parts, not just what one store stocks or one counter-person knows), and make auto parts affordable so vehicles of all ages can be kept reliable and fun to drive. Visit RockAuto.com to order auto parts online 24 hours a day, 7 days a week, and have them conveniently delivered to your door. Need help finding parts or placing an order? Visit RockAuto’s Help pages for further assistance.

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It’s a new week, but it’s the same ol’ story in the Redline Garage. The Jeep 4.0-liter is torn down to a bare block, which means it’s time for a field trip to Thirlby machine shop. This block might represent the best starting point Davin has ever carried through the machine shop door. Of course, that doesn’t mean there’s any less work ahead for the team

“Everything was in really great shape,” said Davin after returning with the freshly machined parts. “We could have just honed it and thrown it back together. Just not worth it though. I mean, you’re already there.” What he’s getting at here is that the engine is already torn down, so there is no point putting off a job now that will only be harder later. The 150,000-mile block didn’t suffer oval-shaped cylinders or any other signs of terrible shape, but it still made sense to spend the few hundred dollars and give it the full machine shop treatment. From the deep clean to the decking and boring, this block is better than new.

There are other parts of the Jeep that need that same better-than-new treatment, and the flywheel is one of them. The starter engages a geared ring on the flywheel to start the engine, and the ring often wears out in just one spot. The reason has to do with the physics of how an engine stops when the ignition is turned off, and which cylinder ends up on the compression stroke to stop the rotation of the crankshaft. The ring gear here could just be flipped, but pressing on a new one that will last a long time is easy enough once we are already in there.

Next stop is the paint booth, but before the engine gets there Davin puts some color on the block along with some other parts on which he plans to do some clean-up work. Casting burrs and sharp edges can make even the nicest paint job look grungy—and when has Davin ever been one to cut corners?

It’s fast progress on this straight-six, so be sure to subscribe to the Hagerty YouTube channel to never miss an update.

Thanks to our sponsor RockAuto.com, an auto parts retailer founded in 1999 by automotive engineers with two goals: Liberate information hidden behind the auto parts store counter (by listing all available parts, not just what one store stocks or one counter-person knows), and make auto parts affordable so vehicles of all ages can be kept reliable and fun to drive. Visit RockAuto.com to order auto parts online 24 hours a day, 7 days a week, and have them conveniently delivered to your door. Need help finding parts or placing an order? Visit RockAuto’s Help pages for further assistance.

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Last week you saw us pull in our most recent project, a 1993 Jeep XJ with a 4.0-liter straight-six. In no time, Davin began tearing into the mill. Things go fairly quickly as the pieces fly off this engine, but this is as much an investigation as it is a quick disassembly. After all, you never know what you might find. Could this Jeep have nothing but good news to share?

This is not the newest engine Davin has torn into (you didn’t forget about the Dodge Demon, did you?), but it certainly is a little nicer than a few others he’s dissected. The Jeep’s driveline comes apart so easily—almost too easily. Suddenly, one exhaust stud lets loose. Of course, it breaks nearly a quarter-inch below the surface of the head. No worry this time, though, since Davin is sourcing as much as he can from RockAuto and it stocks refurbished cylinder heads. One is already in the mail.

The next discovery is a noisy timing chain. It isn’t so damaged that Davin can hear something amiss over the sound of the running engine, but turning the six over by hand prompts further investigation. Removing the timing cover reveals the timing chain is indeed tired—and when it is all said and done, that’s the worst of the story. How refreshing.

The main bearings look darn-near new, while the rod bearings show a decent amount of wear on the thrust surface. Overall, the wear might be so minimal the crankshaft may not even need to be turned down. It’s been quite some time since Davin found this much good news inside an engine, but he’s not kicking back and taking a break. No, it’s time for cleaning and parts ordering, which might mean Davin has some fun upgrades in mind. You’ll have to wait for a future episode to find out what his schemes entail. Be sure to subscribe to the Hagerty YouTube channel to never miss a grease-soaked update.

Thanks to our sponsor RockAuto.com, an auto parts retailer founded in 1999 by automotive engineers with two goals: Liberate information hidden behind the auto parts store counter (by listing all available parts, not just what one store stocks or one counter-person knows), and make auto parts affordable so vehicles of all ages can be kept reliable and fun to drive. Visit RockAuto.com to order auto parts online 24 hours a day, 7 days a week, and have them conveniently delivered to your door. Need help finding parts or placing an order? Visit RockAuto’s Help pages for further assistance.

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Our Mini rebuilt got wrapped up just two weeks ago, but if you thought Davin would wait longer than required to clean the shop before pulling in the next project, you must be new here. For the latest Redline Rebuild, it’s something bright red, two-door, manual transmission–equipped, and absolutely rust-free—just like Davin likes them. This one is a little different than average though, for a few reasons.

Say hello to this 1993 Jeep Cherokee with a 4.0-liter inline-six. It’s the newest car to be on the receiving end of the Redline Rebuild treatment, which means there are a few pieces and processes that will be new. Those surface right away as Davin yanks the engine and transmission onto the floor to be cleaned and prepped for disassembly.

Two of the new elements of this rebuild are the catalytic converters on the exhaust, but they are rusted in place just like most exhaust systems Davin encounters. One cat is also blown out from years of use. Just because it looks good from the outside doesn’t mean it’s functioning properly inside. The transmission tells the same story, as it just doesn’t shift quite right. Another odd hurdle was all the wiring that had to be removed before the engine could be pulled. From the fiddly fuel injector clips to the air conditioning system, it all comes apart, though. Now, it’s time to get cleaning.

This might appear to be a relatively boring build, but we’ve seen Davin’s search history and suspect there will be a few fun parts going into this one. To see just what he has up his sleeve, be sure to subscribe to the Hagerty YouTube channel to never miss a video.

Thanks to our sponsor RockAuto.com, an auto parts retailer founded in 1999 by automotive engineers with two goals: Liberate information hidden behind the auto parts store counter (by listing all available parts, not just what one store stocks or one counter-person knows), and make auto parts affordable so vehicles of all ages can be kept reliable and fun to drive. Visit RockAuto.com to order auto parts online 24 hours a day, 7 days a week, and have them conveniently delivered to your door. Need help finding parts or placing an order? Visit RockAuto’s Help pages for further assistance.

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