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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Enjoy Straight-six stories, opinion, and features from across the car world - Hagerty Media

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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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