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S 6 : Ep 152

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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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Enjoy Redline Update stories, opinion, and features from across the car world - Hagerty Media

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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Enjoy Redline Update stories, opinion, and features from across the car world - Hagerty Media

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 Redline Update stories, opinion, and features from across the car world - Hagerty Media

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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Enjoy Redline Update stories, opinion, and features from across the car world - Hagerty Media

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.

Next episodes

Enjoy Redline Update stories, opinion, and features from across the car world - Hagerty Media

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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Enjoy Redline Update stories, opinion, and features from across the car world - Hagerty Media

When it comes to New Year’s resolutions, there’s one that Davin will never agree to: Go on a diet. After all, the man loves carbs. He couldn’t cut those out of his day-to-day life even if he wanted to. This episode of Redline Update is all about carbs and getting the Mini’s twin SU fuel mixers ready to rock.

The process is simple and starts with placing an order for two new carb kits. The boxes come filled with everything Davin needs to refresh the carbs functionally, but of course Davin is after more than just a functional redo. To help the aesthetics, the stripped-down pieces get a bath in the ultrasonic cleaner before some careful vapor honing to restore the aluminum finish. Only then is it time to re-assemble. Davin’s big tip this episode is to do the carbs one at a time. This way you have a reference point if you forget exactly how the one you took apart goes back together.

While the second carb is in the ultrasonic cleaner, there’s a quick pivot to getting the shaft rocker assembly ready for reinstallation. The assembly comes apart easily and is cleaned even easier by utilizing a tumbler that will do the work overnight while Davin is asleep and dreaming of big blocks and bang shifting quarter-mile passes. The shaft is too big for the tumbler, but he has a tip for making life easier: chuck the shaft in the lathe and spin it at low speed while holding a scouring pad against it. This makes quick work in removing the caked-on oil and grime from years of use. A drill press or even hand drill with a large enough chuck can do the same thing for your projects.

This little engine is making big progress lately, and it won’t be long before the whole thing is back together and on the run stand for break in. Never miss a tech tip or project update by subscribing 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.

Next episodes

Enjoy Redline Update stories, opinion, and features from across the car world - Hagerty Media

The “oil pan” for our 1965 Austin Mini Cooper S needs to be reassembled. Typically an oil pan wouldn’t require so much work, but it just so happens that this one has an entire transmission inside it. Davin gets to work putting every bit and piece of the transmission back together along with several new parts (mostly bearings) that were well worn past the point of using again.

The compact nature of the Mini’s drivetrain is a big part of its character, but it’s also a big source of headache for Davin. The engine’s oil pan houses the entire transmission, and even with small gears that makes for a cluttered assembly. Luckily, he has all his reference materials lined up and everything is ready to go together. A little assembly lube here and a dot of oil there and everything slips together nicely—and we do mean everything. Davin points out that sometimes assembly is a process of elimination game, even when you have the right materials. All the proper parts are on the table, so nothing should be left when the job is done right.

With all the hardware torqued and no “spare” parts left over, this transmission is ready to be mated up to the engine. That will happen on the next Redline Update episode so be sure to subscribe to the Hagerty YouTube channel to never miss a grease-soaked minute.

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.

Next episodes

Enjoy Redline Update stories, opinion, and features from across the car world - Hagerty Media

These days, not much surprises Davin when it comes to events in the engine assembly room. Elements outside his control, however, can provide an entertaining change of pace. Take for instance the incorrect bearing size setback he discovered last week. His plan was to pivot to the transmission, but instead he got something unexpected. A surprise, but not such an unpleasant one.

The first set of bearings that were ordered ended up being too small for the finished machined crankshaft, but a replacement set arrived faster than expected and allowed progress to roll forward (almost) without a hiccup. We say “almost” because Davin might have had the proper bearings, but he lacked the proper tool to check the oil clearance on those bearings. Without micrometer that will do the job, he had to resort to a very basic tool that he doesn’t use often—Plastigauge.

“It’s not that Plastigauge is bad; it’s not,” said Davin about the measuring material. “It’s more that I find it to be a little inconsistent and I don’t have any way of confirming what it tells me with hard numbers.” No matter; it will have to do for this engine, since there is a bit of a deadline looming. Instructions for using this tool are simple: assemble the connecting rods to the crankshaft with a small piece of Plastigauge between the bearing cap and the crankshaft, torque everything down, then disassemble and use the Plastigauge package to determine the clearance. Davin first thought this engine to be a bit tight, but then he remembered that the journals on this crank are much smaller than he is used to.

With a few other parts already installed, the Mini engine is effectively sitting now at the short-block phase. The cylinder head is next, and if the rotating assembly was any indication that will come together quick. Or maybe there will be another odd hurdle? We don’t know, but regardless we will be back next week with another Redline Update. Be sure to subscribe to the Hagerty YouTube channel to never miss an oil-soaked minute.

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.

Enjoy Redline Update stories, opinion, and features from across the car world - Hagerty Media

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