LS Engine Rebuilds: Disassembly Guide • LS Engine DIY (2024)

Before beginning the engine disassembly process, you should already have chosen that corner of your garage you’re dedicating to your rebuild project (discussed in Chapter 2). For disassembly purposes, you’ll need to have some sturdy work tables with adequate newspaper or other clean material to soak up oil and other fluids. Have a bunch of paper towels ready at hand, too.

Small components should be bagged and tagged, but many engine parts are large and bulky (and don’t require labeling since it’s obvious what they are). Don’t just leave the larger stuff lying around, though—generic bins can be helpful to place items in as the engine is being disassembled.

It’s possible to purchase various parts organizing trays and other specialized equipment—if you’re a total neat-freak (or are in the business of rebuilding engines) this is certainly the way to go. But for others, more rudimentary household items like clear plastic bags and permanent markers (along with other stuff like masking tape and mom’s old Tupperware) can perform the task of keeping things labeled and organized just fine.

This engine was installed in a 2004 Corvette Z06, and while the wiring harness and many accessories have already been taken off as part of the process of its removal, others are intact. Still, we’ve attempted to leave on everything that is best considered a part of the engine itself, thereby giving a typical disassembly starting point for most readers. Also, the oil has already been drained, and you should do the same at this time. Get your Work-A-Long sheet ready, and let’s begin!

The intake manifold is the best place to start the disassembly. Remove all PCV hoses, the MAP sensor, and any remaining wiring from the manifold, carefully marking them with masking tape for later identification. This way, you can put things back exactly where they came from later on. All of these items about the intake manifold vary by vehicle and exact engine type, so take detailed notes and photos!

On many Gen III and IV engines, it’s possible to leave the throttle body and fuel rails temporarily attached to the manifold and remove the entire assembly. Here we opt to remove only the fuel rails for the moment (exact style of fuel rails varies by engine). Four bolts hold them down, after which the rails can be gently pried from the manifold and lifted off. Keep an eye out for details like a fuel rail ground strap on many Corvettes and a fuel rail stop bracket at the rear of the driver side rail on Camaros and Firebirds—it will be tough to figure out where small items like these reinstall if you haven’t labeled them.

Ten 8mm bolts hold the intake to the cylinder heads; remove them and the assembly will lift right up. If the manifold is stuck, a little fidgeting will pull the factory seals from the head surfaces. Thanks to the air gap that exists between the bottom of the intake manifold and the rest of the engine, it’s likely that buildup of leaves, oily grime, and other dirt will now be revealed. Be ready with some paper towels, or even a vacuum.

The oil pressure sensor is located at the top rear of the engine. In some engines the sensor threads directly into the block (as here), while in others it threads into the valley cover. A special socket tool can be purchased to remove/install this item (even a deep socket isn’t long enough for taller style sensors), but an open-end wrench can also work just as well if you’re careful. Save this sensor for possible later reuse.

Gen III engines have their knock sensors mounted beneath the intake manifold, in the valley cover area. Pop off the knock sensor wiring harness, but use care on the plastic connectors (pliers gently squeezed and jiggled work well) as they can become brittle in this hot environment over time. Then, use a deep socket to remove the knock sensors. Note that Gen IV engines have their knock sensors mounted down low on either side of the block, as shown in the final photo (note that the sensor shown is actually a Gen III unit installed into the Gen IV location—that block was swapped into a vehicle that was originally Gen-III equipped. See “Block-Swapping Points of Interest” on page 46).

The valley cover can be removed next via ten or eleven 10mm bolts. Some engines have a PCV system integrated into this cover, as does this LS6 unit. Also, some Gen IV engines will have the Active Fuel Management system located here, but because everything in this system is integral to the valley cover (technically called a LOMA on those engines), its removal does not require any additional steps from those shown here.

The coolant air bleed (a.k.a. coolant vapor) pipes, which run between ports at the front and rear of either cylinder head, vary in style by vehicle. Some engines have a pipe connecting the fronts of the cylinder heads together and a separate pipe connecting the rears. Others have a single pipe that connects all four (which will require these pipes to be removed before the valley cover), and some don’t connect the rears at all, as is the case here. No matter what style you have, they are removed with a 10mm socket and, along with their bolts, set aside for later reuse. You should make a note to buy the correct type of new seal for these (some have an O-ring, while others use plate-style gaskets).

If you haven’t done so already, the ignition coils can come off. The individual coils (as well as their wiring harness) can stay on the brackets (if equipped), and each bracket removed as a unit. In this case only remove the bolts holding the bracket to the valve cover; on most engines, this translates to five 10mm bolts each.

All LS engines except 1997 and 1998 LS1s had four centralized bolts holding each valve cover to the cylinder head.(These early LS1s had their bolts around the perimeter.) With the bolts removed, the covers should come off with nary so much as a gentle pry.

Loosen all sixteen rocker arms via an 8mm bolt on each. Some bolts will turn out more easily than others, as some rockers will be holding their respective valves open at this point, while others will not. It’s best to turn each bolt all the way out but leave it in its respective hole. This way, all the rockers on each head can be lifted off while still sitting on the rocker arm pivot supports (shown; note that certain engines such as the LS7 have no such separate supports—their pivot supports are machined directly into the head). Each rocker and its bolt can then be lifted off of the support, labeled, and set aside for possible reuse. Please note: when removing rockers on an engine equipped with strong aftermarket valve springs, it is recommended that you only remove each rocker bolt when its respective valve is closed. This prevents possible thread damage in the head.

The sixteen pushrods simply slide up and out of the cylinder head. Use an organizer tray (one of these works well for rocker arms too) or just label each carefully to show where it came from. Reuse is theoretically possible, though LS pushrods are often found to be bent and must be replaced. See Chapter 4 for more information.

Remove the dipstick tube (if equipped), which is held to the passenger side cylinder head by a 15mm bolt. Simply pull upward to remove it from its hole in the engine block behind the exhaust manifold. Inspect its O-ring seal for any damage; if there is none, it will be OK to reinstall it on your rebuilt engine.

Remove the spark plugs, then the exhaust manifolds via six bolts a side (if you haven’t done so already). Again, this engine was equipped with aftermarket headers, so yours will almost certainly look different. Mark any air injection system tubing and brackets for later reinstallation—not all vehicles had such a system, though this one did, as you can tell from the 2-bolt flange sticking out at the top middle of the header.

Though we’ve been dismantling this LS6 as it sits on its Corvette subframe, we’ll need to get it onto an engine stand soon. If you haven’t done so already, remove everything at the rear of the engine down to the flywheel or flexplate, including the transmission/bellhousing and torque converter or clutch (as shown here). Some light prying may be needed on some of these components in order to facilitate removal, and a pry bar held against one of the engine-to-transmission dowel pins can be used to help keep the flywheel or flexplate from turning while loosening clutch or torque converter bolts. A flywheel holding tool is a better option.

All manual-transmission vehicles had a pilot bearing or bushing pressed into the back of the crank for the transmission input shaft to ride in. Before the engine stand gets in the way, now is a good time to remove it. Different types of puller tools are available on the market, one being this slide hammer—but we advise you save some money and have your machine shop remove and replace this bearing for you.

Also in the interest of making the engine less bulky and better able to be mounted on an engine stand, remove any remaining large and easy-to-access engine accessories that you may not have already. These might include the water pump, alternator, and power steering pump and reservoir, among other items (depending on application).

Discussed in Chapter 2, engine stands are readily available at nearly any large auto parts outlet, and now is the time to put it to use (if you haven’t already). Make sure you are using a quality stand, hardware, and lifting equipment, and get at least one other person to help you. Bolt the mounting portion of the stand to the rear of the engine block using high-grade, long metric bolts. Adjust so that the engine will be mounted as low in the stand as possible (to best enable later access to bolts at the rear of the engine). Then, using your engine hoist or similar device, lift the engine (don’t forget to disconnect the engine mounts!) and carefully slide the mounting portion into the remainder of the engine stand. The engine can now be easily worked on from any angle!

With the engine now on a stand, any remaining brackets and accessories that may have been mounted low and difficult to access before can now be removed. These include the starter motor, engine mount brackets, and anything else you may not have removed from the outside of the block already (all of which vary by vehicle).

Before removing the cylinder heads, take out any screw-in plugs and sensors. This will help avoid damage to these parts once the heads have been removed. On this LS6, the passenger side head has a plug at the rear that is removed with an 8mm Allen key, and the driver side head has a coolant temperature sensor at the front that is removed via a deep socket. Cylinder head plug/sensor type and location may vary, so note where each of these will reinstall later (as well as any ground wire and accessory bolts located at the front and rear of each head, some of which you may have dealt with already).

Remove the five M8 thread cylinder head bolts located along the top of each head, followed by the ten larger M11 (or on some engines, M12) thread bolts on each. The M11 bolts will be very tight and will require a breaker bar to dislodge. These M11 bolts can’t be reused as they are a torque-to-yield type, but hang onto them for now. You will need to inspect them and determine which type to buy (GM used different head bolt lengths that varied by model year) and you will also need them during pre-assembly. A magnet may be needed to lift the under-the-valve-cover M11 bolts out of their holes as they sit in deep recesses in the head.

Once unbolted, many Gen III/IV cylinder heads come off easily, but this could also be a slight challenge if the head gaskets have adhered to the block and head surfaces (particularly true of earlier-style, graphite-layered gaskets). Taps from different directions with a rubber hammer can help dislodge the heads. Another technique is to use a hammer shaft in an intake port; just pull it toward you and it should lift the head off. Label which head was which, and carefully set them aside on a soft surface (such as wood blocks) so as not to scratch or otherwise damage their deck surfaces.

Assuming the gaskets didn’t already come off stuck to the heads, remove the head gaskets from the block surface. They should peel off easily but may leave some residue (later-style MLS gaskets like those shown will leave much less). Don’t worry about scraping off the block surface; aluminum blocks in particular can be damaged if this is done incorrectly, and besides, let your machine shop worry about this kind of cleaning!

Found at the front and rear of each deck surface of the block, a total of four cylinder head locating pins (a.k.a. dowel pins) help position the cylinder heads and head gaskets on the block surface. They can be removed using pliers. While you can theoretically reuse these, you should probably just discard them and get a new set for later.

Remove the plastic valve lifter guide trays. There are a total of four, each spanning two adjacent cylinders and held by a 10mm bolt. With the bolt removed, lift the guide up and out. Most lifters (a.k.a. tappets) will come out with the guides, so be careful they do not slide out once the tray clears the block (and possibly land on the floor). Exact guide tray shape varies by engine, so yours might not look quite the same as shown.

Some lifters may not come out with their trays, be rather may remain stuck in the block due to sludge deposits or abnormal wear. If needed, use pliers to remove them; but a magnet might do the trick just as well. Remember to mark where each lifter is coming from for diagnosis purposes (also, used lifters are a unique match to their bores, though their reuse is not recommended—see Chapter 4 for more information).

Install a flywheel holding tool onto the flywheel/flexplate if you have one. Absent access to one of these, an assistant can also hold a large pry bar in the teeth on the outside perimeter of the flexplate or flywheel to help keep the crank from turning (necessary during steps 28 and 30 as well). The 24mm crank bolt will be very tight! While a breaker bar is best to use, this is one case where it is usually OK to use an air ratchet to remove this bolt if you must—it should not damage the crank threads. The crank bolt cannot be reused; however, it will help in later reinstallation of the harmonic damper (among other things), so hang onto it.

Remove the harmonic damper (“balancer”) with a 3-jaw puller. If your puller does not have the correct cone-shaped fitting to rest in the front of the crank snout, you’ll need to thread your old crank bolt in and either keep backing it out as the damper moves forward, or acquire another, longer crank bolt (or one with a ground down outside edge) to push against so the damper can move freely off the snout.

Up to this point, we’ve been working with the engine mounted right-side-up on its stand. To provide better access to upcoming components, now is the time to flip the engine over. Make sure the oil has been drained before doing this, and because you will have some amount of fluid dripping out of the engine, have a pan ready to catch coolant and residual oil (a specific one made for an engine stand works best). This type of gooey mix will require special disposal—don’t mix it with the oil you’re taking to the recycling center! (To minimize coolant splash here, consider removing the engine block coolant plugs before turning the engine over; see step 59.)

On most engines, six 15mm bolts attach the flywheel or flexplate to the crank. Once they are loose, you must remove your flywheel holding tool (or pry bar!). Some light hammering around the perimeter will help a stuck flywheel or flexplate come off. You may be interested to note that oftentimes, an “extra” hole in the flywheel or flexplate surface lines up with a corresponding hole in the crankshaft (seen just above the middle and index fingers in the photo) on LS engines.

The oil pan is fastened to the bottom of the engine block with an array of 10mm bolts, the majority of which are short bolts securing the pan to the engine block (there are two securing the pan to the front cover). But in addition, there are two longer bolts at the rear that extend all the way from the bottom surface of the pan into the rear engine cover. Since some Gen III and IV oil pans are a two-piece design (as is the case with this Corvette pan), don’t get confused and remove the bolts holding the pan together—they can stay in for now.

Some light tapping and prying may be needed to dislodge the pan, but don’t go crazy and damage it: it’s a stressed member of the engine! Once it’s free, begin lifting up, noting that you may have to jiggle back and forth a bit for the pan baffles to clear the pickup tube that’s still attached to the engine (dry-sump engines excepted). As you can see, the pan can be removed with the oil filter still attached if desired (older small-blocks had filters that threaded directly to the block). You’ll need to remove its baffles and sensor(s) (to allow you to clean the pan out) later, all of which vary by pan type. For now, cover any oil passage openings, then drill any rivets holding the pan gasket to the pan and throw the gasket away.

Twelve 10mm bolts hold the rear engine cover to the block. The cover will be reused, so don’t damage it by prying too hard and scratching the underside; this can result in an oil leak.

Eight 10mm bolts secure the front cover (a.k.a. timing cover) to the engine block. Note that the Gen IV front cover is slightly different and has the cam sensor mounted in it—such a cover can be removed with the sensor intact, so the procedure is the same. Some engines also have part of the VVT system mounted here, so you should photograph your engine’s particular layout for reinstallation later.

With the engine covers removed and the oil-soaked internals exposed, one can have the first good look at anything that looks suspicious in terms of engine wear or damage. Check out the excess metal particles located in this engine’s oil pickup screen and the large metal chunks that appeared to be piston ring pieces lying about. These told us to stay on our toes, note what we’d seen, and be doubly diligent in making a record of any component wear or breakage irregularities as disassembly proceeded.

The oil pump pickup tube (GM calls this entire assembly an “oil pump screen”) needs to be removed next. A 10mm bolt holds the tube in the oil pump inlet, and a 13mm nut holds the other end of the tube to the crank oil deflector and main cap bolt. You will note that the tube installs into the pump with an O-ring; there were different styles of these used, so hang onto yours so you can compare when buying a new one. (Note that on dry-sump engines, the pickup tube is part of the oil pan, so this step is not necessary.)

Remove the remaining nuts holding the crankshaft oil deflector (a.k.a. windage tray) to the main cap bolts, then simply lift it off of the engine. This item will be reused, and in Chapter 7, we’ll show you how it can be modified if you’re installing a longer-stroke crankshaft into your rebuilt engine.

Four bolts come undone and the oil pump slides off the front of the crank snout. We should note that aftermarket bolts and pump spacers have been used here to move the pump forward and accommodate a so-called double-roller timing chain, but most factory setups look very similar. You may now flip the engine right side up on its stand.

The camshaft sprocket is held on by three bolts (or, on later engines, one centrally located bolt). Even with these removed, the sprocket will likely be stuck onto the cam’s locating pin. Some prying (don’t damage the front cover sealing surface!) and rubber hammer taps about the perimeter will likely be required to coax it off. Once that’s done, the cam sprocket and chain slip easily off the crank sprocket

The crank sprocket is a press-fit design, and chances are you’ll need a 3-jaw puller to get it off. As when pulling the balancer, an alternate crank bolt may come in handy to give the puller a surface to push against. You can let the shop servicing your crank worry about removing this sprocket if you like, but either way, the inevitable wear of the gear teeth means that this sprocket needs to be replaced with a new one. Note that factory and factory-style sprockets also double as an oil pump drive gear, and that underneath it the crank is keyed. This key may be stuck in the crank, but if you are able to get it out easily, save it for later reuse or remember to buy a new one.

It’s almost time to remove the cam, but before you can do so, a couple of preliminary steps. The first: on a Gen III engine, you must remove the cam sensor at the top rear of the block. Remove the retainer bolt, and the sensor will slide out the top—a gentle screwdriver pry may be needed to dislodge it. (If your engine is a Gen IV, the cam sensor came out with the front cover.)

Remove the four cam retainer bolts (which may be TORX-head) and retainer plate at the front of the engine block. This plate has an O-ring seal on the back that you’ll need to inspect for damage. Set it aside for now.

As with any pushrod V-8, the camshaft is bulky and long, and there is virtually nothing of it to grab onto for the first few inches as it comes out of the block. To remedy this problem, you can install long bolt(s) into the front so that you have some leverage. Or, as here, insert a long 3/8 extension into the hollow bore in the center of the camshaft (this may not be possible with all cam designs). Keep upward pressure on the cam so that the lobes do not fall onto the cam bearings or other metal parts, possibly damaging the cam (they can touch, just avoid too much jostling). For the first couple of inches, you can also reach around the back of the engine and guide the rear of the cam. Slide the cam toward you slowly until it’s out; all cam bearings are the same size I.D. so you’ll have to hold it centered the whole way.

It’s time to remove the rotating assembly, but before doing so, take a moment to feel the tops of the bores. On high-mileage engines, sometimes there will be a ridge from the rings wearing along the cylinder walls. If this ridge is exceptionally bad, you can buy a special tool to cut it down, as it may hinder piston removal (the rings will hang up). However, you can also damage the block and render it unusable if you don’t use the tool correctly, so the alternative is to simply force the pistons out. This might result in damaged rings or pistons, but you won’t be reusing them anyway (and there is almost zero chance the block will be hurt). The choice is yours, make it wisely.

Flip the engine upside-down. A crank turning tool can make the process of turning the crankshaft much easier (particularly later during pre-assembly and final assembly), but if you haven’t invested in one at the moment, you can also just install your old crank bolt and use a 24mm socket to turn it (shown). We’re about to remove each piston/rod assembly one cylinder at a time, and having a piston at BDC gives the most room to work—so pick a piston to start with and turn the crank until that piston is at the bottom of its bore.

Now, break the rod bolts free with a long-handle wrench or breaker bar. Turn each bolt out a few threads, then stop—don’t remove them all the way yet. Tap each bolt head with a hammer to help separate the rod from the cap. This is needed because the rod and its cap will be stuck together pretty well. Then, with the rod bolts still in, begin to hold the rod from underneath. Remove the bolts the rest of the way and set the rod cap aside (along with the bearing shell, though this may stick to the crank journal). Remember not to let go of the rod at any point once the cap is off—though normally the rings will provide enough drag to prevent the piston/rod assembly from sliding out on its own, you can never be too careful!

Probably the simplest technique for piston/rod removal involves using the butt end of a hammer against the bottom of the rod. Make sure it’s a soft-handle hammer to prevent scratching the crank journals or other components! Hold pressure against one of the flat mating surfaces on the end of the rod and slowly push the piston/rod assembly downward. If the piston doesn’t want to move easily, it may need some tapping, but make sure the rod isn’t hung up on the block before attempting this (Note: If there is the aforementioned ridge at the top of the bore, this may cause a hang up and require a hard whack to get it out—do not hit hard if there is anything else interfering.) You don’t want the piston/rod to hit the floor as it comes out, so be ready to grab it from below and pull it out the top of the bore.

With the piston/rod assembly out, immediately reinstall the rod cap in its correct orientation (this will be fairly obvious for most rods) so that you can’t mix it up with the other rods. The same should be done with both bearing halves for inspection purposes. Repeat steps 45 through 48 for each cylinder. Note that most Gen III engines have rods pressed to the pistons, whereas all Gen IVs have floating pins held in by clips; in either case, you can leave the pistons assembled to the rods for now and disassemble them later (or have the machine shop do it for you, which is required in the case of pressed pins).

One of the ongoing themes of proper engine disassembly is that you should make note of any evidence of wear and tear that looks suspicious; this way, you know what to inspect in more detail later. With this particular engine, however, the root of our previously found particle matter became obvious when the number seven piston was removed. Damage to this piston is not all that uncommon, especially in LS engines that have been exposed to aftermarket forced induction. The consensus is that it has to do with cylinder seven drawing its intake manifold air furthest from the throttle body, and fluid mechanics dictates that it gets a bit more air pressure than the other cylinders (and so runs a little leaner). Add a too-lean custom engine tune into the mix, and you’ve got a recipe for disaster—and the need for a rebuild! This engine block may have too much cylinder wall damage to be reused, but the machine shop will have to make that call.

It’s about time for removal of the crankshaft. First, remove the crankshaft position sensor at the rear of the passenger side of the block. Remove its retaining bolt and gently pry outward as needed. Inspect its O-ring seal for possible reuse.

There are five main bearing caps on the Gen III/IV, and they normally are identified with a factory stamping: number 1 at front, number 5 at rear. These pieces are uniquely machined with the engine block and must not be mixed up, so if there is any question as to the factory markings, make your own markings now using a non-intrusive method.

Two M8 bolts (10mm head) hold each main cap from either side, so there are a total of ten to remove. GM says to discard these bolts; however, they are easily reused if desired and will just need some sealant during reassembly, so bag and label them if you plan on doing so.

Remove the twenty M10 main cap bolts, some of which are studded to enable connection of the aforementioned crank oil deflector and oil pump pickup tube. For the outer ones (the ones with studs sticking out the top), you’ll need a 15mm deep socket. The inner ones have 13mm heads.

To remove the main caps, GM sells a special tool that utilizes a slide hammer. But we recommend simply using two medium-size 3/8-inch extensions or pry bars to lift each cap gently from the underside. A back-and-forth rocking motion can also help, so have the extensions or pry bars facing opposite directions if need be (not shown). The caps will be tight in there (thanks mostly to the matched machined fit between each cap and the block), and this is particularly true of the thrust bearing cap (number 3, shown being lifted out). Remove the lower main bearing shells as well, which may stick to the crank journals, and keep them with each respective cap for inspection purposes.

With the main caps removed, the crankshaft is free to come out. Use of gloves with a grippy surface is strongly recommended thanks to the heavy nature of the crank, but at least clean the surfaces you’ll be grabbing to get the oil off. Lift straight upward and wiggle the crank a little to get it out. Don’t let any of the rod or main journals get scratched. And don’t drop it! Set it aside in a safe place, preferably in a dedicated crank box or on wooden V-blocks. Note the reluctor ring at the rear of the crank: we’ll talk more on options regarding this item in later chapters, but for now, just be careful not to let it contact anything as it can easily be damaged.

Remove the upper main bearing shells that are still sitting in the block, using a screwdriver to carefully pry them out as needed. Label where each one came from for diagnosis purposes (keeping them with that crank journal’s main cap is best). They will not be reused, however.

The block is now nearly bare, and you can now remove all remaining engine block plugs, starting with the metal oil gallery plugs. Some of these plugs have washers that, if undamaged, can be reused, so don’t lose them if for some reason they are not attached to the plugs. Exact location of plugs may vary by engine, but the ones you’ll typically see are: Front oil gallery plug (press-in, far right of photo): This must be removed to enable full cleaning of oil passages. As a long rod is required to hit it from the back, you may leave this one to your machine shop. Front left (driver side) oil gallery plug (shown being removed). Rear left (driver side) oil gallery plug (not shown here; location is near upper right corner of photos of next step).

The rear oil gallery plug (which is made of plastic and sometimes called the barbell restrictor) gets sandwiched into its place in the block behind the rear cover. A pick or similar instrument will likely be needed to coax it out of its hole in the main oil gallery. If its O-ring is OK, it can be reused; but this plug is inexpensive and should be replaced.

The final block plugs to remove are the coolant plugs, which include: Right rear (passenger side) coolant plug (top photo, small plug). Driver side coolant plug (bottom photo, large plug). This plug will be located toward the rear of the block on some engines, and toward the front on others (shown). It is also the location of the engine block coolant heater on vehicles so equipped.

With only the cam bearings still in place in the block (leave their removal to your machine shop), we’re down to the bare block, and the first important step in your rebuild project is complete (except for cylinder head disassembly). In Chapter 4, we’ll take a closer look at the parts we’ve just removed and talk about options for repair, replacement, and upgrades.