It high time for assembly to begin on the Jeep straight-six living in the Redline Garage. The steps on a short block go fast, but that doesn’t mean we overlook any essential details. Davin, after all, is never one to take shortcuts. However, sometimes that means taking literal cuts. Stay with us.

The engine block recently returned from a second machine shop trip to re-cut the deck height, and it was  also re-cleaned so it can be ready for final assembly to begin. That process starts with the freeze plugs—and also a few threaded plugs—in the case of this particular engine. Those threaded plugs are a taper pipe thread, which means they don’t technically need any sealant of coating. Davin points out that assembling dry is perfectly acceptable but more than likely will lead to the plugs becoming all but unremovable in the future. A quick dap of teflon sealant will keep them serviceable.

Then it is on to the pilot bushing in the crankshaft, the cam bearings set into the proper places, and then the final torque of the crankshaft main bearings. Toss on the pistons rings and send those into the bores and things were going swimmingly. Almost too smoothly.

The combination of parts Davin uses is all Jeep in origin, but that doesn’t mean they were designed to function together.  The first time these incongruences appear is just as the harmonic balancer is installed on the snout of the crankshaft. The new balancer sits a little further in, and thus Davin has to do some fabrication with the plasma cutter and lathe to make an appropriate “washer” to ensure everything is held properly by the crankshaft bolt. In the end, it’s a fairly easygoing and quick process.

Will Davin keep this pace as the assembly continues next week? We all hope so, but even if it doesn’t you’ll get all the grimy details in the next episode of Redline Update. Be sure to subscribe to the Hagerty YouTube channel to never miss a new episode.

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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The light has appeared at the end of the tunnel for Davin and the Jeep engine. It’s still quite far away, but he can see it. Before taking steps toward that light, another trip to the Thirlby machine shop is required to lower the deck height in an effort to raise the compression. And another issue pops up that needs to be discussed with the machinists.

Before loading up and heading off to re-deck the block, Davin takes the time to check the oil clearance on the main bearings. This is an important step, because while most of the time the numbers come out fine, engine building is always a game of “trust, but verify.” With the main caps torqued to spec, Davin measures the diameter of the bearing location on three axis. What he finds is a little uncomfortable. To him, the holes seem a little egg-shaped and also about half a thousandth too wide.

The machine shop doesn’t agree, however. Before bolting the block into the machine to trim the deck down, they use thier measuring tools to “sanity check” Davin, and they certifiy him insane. Davin is a known perfectionist, and on this job the machine shop guys think he might be going just a bit too far. The return on investment of getting this absolutely perfect is pretty slim, and that’s why they advise it would be best to leave this one alone. Those clearances might be a fraction off, but they’re still well within a usable tolerance.

Back at the shop, Davin is the first to admit things are way out of order at this point. A freshly painted block shouldn’t be going to a machine shop, and a block back from the machine shop shouldn’t be getting casting cleaned up again. It makes for even more cleaning work before assembly can begin, but we all know Davin is not one to take the easy route just to get things done. With any luck, things will come together next week, but then again, another roadblock might also appear. To find out for yourself, 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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Building an engine is vastly different than assembling one. One involves proper fitting of parts—the other, merely bolting things together. Today Davin takes you on a deep dive into one of the key parts of engine building, whether you’re aiming for performance or basic conveyance: compression ratio.

The concept is simple: The amount of space inside the cylinder when the piston is at bottom dead center compared to the amount of space inside the cylinder when the piston is at top dead center. As anyone who’s built an engine will know, however, that which is easily summed up is not always the easiest to execute. Accurately calculating compression ratio takes a bit of math, a bit of knowhow, and some antifreeze (seriously).

Davin starts by obtaining the size of the combustion chamber in the cylinder head, using a plate of glass and burette to measure its exact capacity in cubic centimeters. With some basic math, he calculates the cylinder volume, and all that is left is the volume added or subtracted by the piston dish or dome. In the case of our Jeep’s 4.6-liter engine, the piston is dished. While Davin could measure that additional area exactly the same way he did the combustion chamber, he decides instead to set the piston a small distance into the cylinder and grab a pencil to do the math and get the final number.

Compression ratio determines a few very important characteristics of an engine. The one Davin is most concerned with is this straight-six’s ability to run on “pump gas.” To Davin, that means 87-octane fuels. For an engine to run on fuel that volatile without any knocking, it is best to target between 9 and 9.5:1 compression ratio. He calculates that this particular Jeep’s engine compression would be around 8.5:1 as it sits now. Not ideal.

He devises a simple fix: Use a thinner head gasket and take a quick trip back to the machine shop to shave the deck height just a smidge more. With those changes made, this engine will be ready for final assembly, a process which Davin can begin with confidence, knowing that all the parts will play nicely together and that the mill will run as he expects it do when it’s time for first start-up.

To see the rest of the assembly and other tips and tricks our resident engine builder, be sure to subscribe to the Hagerty Youtube channel.

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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