Chevy 348-409 Engine Block Guide (2023)

The good news about 348 and 409 blocks is there were more than 18 different Chevrolet W-engine factory blocks built from 1958 to 1965. The bad news is that most were built more than 50 years ago and are showing their age, and many original blocks have been rebuilt several times. On top of that, rebuildable 409 blocks are hard to find and getting more expensive all the time. Original 409s are highly coveted and a decent block often sells for about $5,000 while the 348s are much more abundant and often go for about $1,500 in rebuildable condition.

If you’re restoring an Impala or another Chevy car or truck with a rebuildable block, you already have the foundation for your engine build. But if you’re looking for an engine to build, old iron blocks are not the only option. Companies, such as World Products and Bob Walla Racing, offer new aluminum blocks based on the original W. Certainly, if you’re considering a high-performance build of 550 hp or more, an aftermarket aluminum block provides far more strength and has many enhanced features that are covered in this chapter. Therefore, these blocks are a far more reliable and cost-effective alternative for a high-performance build.

Chevy 348-409 Engine Block Guide (1)

The World Products Merlin 409 W block follows the same basic architecture of the stock W engine but incorporates Chevy big-block features. With this platform, you can build a high-performance street as well as a full-race engine. It accepts big-block Chevy camshafts, connecting rods, timing chain and cover, and a crankshaft stroke that’s up to 4.250 inches.

Chevy 348-409 Engine Block Guide (2)This Tech Tip is From the Full Book “HOW TO REBUILD & MODIFY CHEVY 348/409 ENGINES“. For a comprehensive guide on this entire subject you can visit this link:

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If you opt for an original block, most dedicated W enthusiasts can find a useable one for building a 348 or 409, but it may take some time and patience. The trick is to know what you’re looking at when you do find one. And if you cannot find a sound OEM 348 or 409 block for your engine build, aluminum aftermarket blocks are available, and these blocks are ideal for a max-performance build.

The first question W hunters typically ask is, “Just how many did they make?” As with block casting numbers (or any casting numbers for that matter), the information on just how many blocks were made by Chevrolet is incomplete. We do know, however, that production of the 348 was not shut down when the 409 began. Chevrolet continued making the 348 to use in trucks, going into 1965. In fact, because the 409 was introduced in early 1961, the 348 was offered to car and truck buyers for more model years than the 409. The 348 ran from 1958 through 1965 and the 409 was produced from 1961 through 1965, or seven years to four.

Block Identification

One of the quickest ways to spot a 348 or 409 block is by its front. W engines have the two water pump inlets to the block spread out across the front. The holes are located very close to the outside of the block and their inlets (with one side flattened) are closer in shape to a diamond than a circle or oval. They are located just above a freeze plug and use two bolts to mount the water pump on each hole. If the block being inspected still has the water pump attached, it’s easy to see that the centers of the two bolts holding the water pump to the block are on an angle, as opposed to being vertical.

The other way to identify the difference, although it is a little more difficult, is to look at the shape of the cylinder bores. Where the bores meet the deck, they look slightly oval rather than the usual round. It’s not something normally seen on first glance but once the shape is determined, it is a quick confirmation for a W engine.

Chevy 348-409 Engine Block Guide (3)

One view of the World aluminum W block shows the steel main caps and distinctive water pump bosses outboard on the face of the block. There are four-bolt mains for all crankshaft journals and stout webbing underneath the full-width main caps.

Chevy 348-409 Engine Block Guide (4)

Chevrolet placed an “X” on the front of the block for the passenger 409 engines and the truck 348 engines, so if your engine has X in this location, it’s a 1962-or-newer model.

The external physical differences between a 348 and 409 block are virtually nonexistent. Although some folks use the location of the dipstick to determine the engine size, the oil pans determine where the dipstick is located, not the blocks. Therefore, since the 348 and 409 oil pans are somewhat interchangeable, identifying a block using dipstick placement is not 100-percent foolproof. If the block has had one or both of the heads removed, checking the bore can provide solid clues. But as some blocks may have had work done to them in the past, bore size IDs are not always proof, either. Casting numbers are still the fastest and most accurate way to identify a block.

Design Features

The cast-iron W blocks distinctly differ from small- and big-block Chevys in a few areas. The first and most obvious is the water pump inlet hole locations in the block, which are spaced farther apart than on small- or big-blocks, and the openings are diamond shaped rather than round. The cylinder reliefs are the next identifying feature, which are cut into the piston bores as detailed earlier.

Both the 348 and 409 were used in truck applications, and these engines had two relief cuts in the bore to reduce compression. As a general rule, those two cuts equal the 7.5:1 compression typically seen in a W engine for trucks. One relief cut indicates a block with 9.5:1 compression for passenger cars. Both truck blocks are excellent starting points for building a strong W engine.

The last identifying feature is the angle of the deck. While small- and big-block Chevy engines have 90-degree decks in relation to the piston bore, Ws have a 74-degree deck.

Only two sizes of W engines were offered, and therefore it’s much easier to identify a W block than a typical small- or big-block Chevy engine. That’s because those two engines had a longer life and offer literally dozens of variations. For W fans, it’s either 348 or 409. Yes, there is the elusive and extremely rare Z11, and finding one of those would be the Holy Grail of W engines. But interestingly, the Z11 engine block is actually a production 409 model, even to the point of sharing the same casting number. For the Z11, it’s all about the heads and intake and in a minor way, the crank and rods.

Casting Numbers

My research found ten block casting numbers that apply to the 348 and eight for the 409. The Z11, as previously noted, shares the same casting number as one of those 409 blocks. These casting numbers are found on the rear of the block, on the flange that goes from the block to the bellhousing, and on the driver’s side of the block as it sits in the car or truck. They are easy to read as they are raised letters and numbers cast with the block. This is in opposition to a serial number or VIN that is stamped into block on the front of the passenger-side deck where it meets the head. The other difference is casting numbers are the same for their respective parts while VIN and serial numbers are records and no two are alike.

Chevy 348-409 Engine Block Guide (5)

The casting number is found at the driver-side rear of the block. Cast- ing numbers reveal vital information about the engine, including model, horsepower, and whether it’s a car or truck engine.

Date Codes

In the era the Ws were built, vehicle identification numbers (VIN) were not always used. A VIN can be used for determining the age of a block and is stamped into a pad on the front of a block. Date codes were cast into the blocks. The date code of a W can be found on the back end of the block, on the skirt where the bellhousing mounts to the block.

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Another number that is found in the same area is the block’s casting number, and that can be used to determine the application. Typically, the date code starts with a letter that signifies the month cast: “A” equals January, “B” equals February, and so on. The middle number or numbers indicate the day of the month it was cast (1 through 31). The last one or two numbers indicate the year: “0” for 1960, “63” for 1963, and so on. As these engines were made only from 1958 to 1965, it’s easy to follow.

Engine Design Features

The 348 and 409 heads have six bolts per cylinder and fit either block, but even though both heads fit, they are not readily compatible. Therefore, you should not bolt together mismatched heads and blocks because it could lead to out- right engine failure. The 409 heads’ valves may impact the smaller bore on a 348 block. The bores differ enough between the two W engines, so the heads and the block should be of the same displacement. When swapping in the other direction, such as putting 348 heads on a 409 block, everything fits, but the engine suffers from lack of breathing and is less powerful.

The other factor in swapping heads is the use of the correct intake manifold. W-engine heads need to match the intake and vice versa or additional problems occur. So, keep in mind that the heads do bolt up to different blocks, but it is not recommended to do so.

Deck height is one of the more critical measurements of W blocks. To extract more displacement from W engines, General Motors engineers used a higher deck height than on the small-block Chevy. With the W’s angled decks, it may appear to be a bit confusing, but it really isn’t. A block’s deck height is typically measured in the center of the bore down to the centerline of the connecting rod on its correct crankshaft journal. The W block height is no different, despite the 74-degree angle. The deck heights of the two engines are the same at 9.6 to 9.69 inches. Again, as the rare Z11 is actually based on a production 409 block, it is the same. The bore spacing for both the 348 and 409 is 4.84 inches. This is only slightly bigger than the small-block’s 4.04 inches and confirms how Chevy wanted to be able to install a W engine in the footprint of the small-block.

W engines, much like their small- and big-block cousins, have no skirts on the side of the block at the crank- shaft location. The plane of the block

where the oil pan mounts is on a centerline just above the centerline of the crankshaft’s main bearings. This aligns the many forces on the crank- shaft and block where they meet and provides the optimum strength of the junction. Four-bolt main-bearing caps would have helped give the blocks more strength in holding the crankshaft and distributing its forces, but GM engine designers were still more than a few years away from using them so they never appeared on any W. If you are taking your W engine into higher RPM, a four-bolt main bearing cap conversion kit is a wise idea.

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This original W block has been cleaned and is ready for assembly. The block must be cleaned numerous times during the machining and assembly process to remove machining chips, grind- ings, oil, and other debris that causes damage if left inside the block during final assembly. Even fluids for testing for cracks need to be removed.

(Video) Building A 409 From The Block Up - HorsePower S12, E10

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Only some of the preliminary machining has been done on the Bob Walla aluminum block, but at this stage, the relief cuts for controlling compression are roughed in. That way, when the block’s machining has been completed, the relief cuts are already in place. More machining is needed for a block to be ready to use, but this block is a prototype.

Chevy 348-409 Engine Block Guide (9)

Looking at the top of the Bob Walla block shows cross webbing that adds strength to the block. Almost all aftermarket blocks have this webbing both on top of the block in the lifter galley and below on the main journals for as much strength as possible.

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There are two pins in the deck of the block for locating the head and gasket. Use fresh freeze plugs in a build. Freeze plugs usually rust out and can be a problem to replace in the car. Changing them out during a rebuild is inexpensive and easy.

The main caps are 2.4985 inches and the rod journals are 2.200 inches. All W engines have two-bolt main caps, and many engine builders elect to convert the W blocks to four-bolt main-bearing caps when using a bigger-stroke big-block Chevy crankshaft. The end-bearing caps remain two-bolt units while the three-center main-bearing caps are converted to four-bolt units. Therefore, you need to purchase a set of Mark IV four-bolt main-bearing caps and coordinate

with a machinist to get the work done. Interestingly, the Z11 block did not even come with four-bolt mains, but certainly there is enough material on the block webs to support a four-bolt conversion.

The transmission bolt pattern on the back of the two W-engine blocks is the same as on the predecessor small-block and the big-block that followed the W. Therefore, most Chevy transmissions bolt up to the 348 or 409 block.

Chevrolet used the same engine mounts as on the small-block and even mounted them in such a location that swapping the two engines is easily accomplished. These mounts and their corresponding holes in the block are the same for both engines and all models. The factory engine mounts are a combination of rubber and steel and use the same triangular pattern of three bolts to mount to the block. A matching mount is used on the frame of the vehicle and one longer bolt connects the two when installing an engine.

Washing and Magnafluxing

Before you choose to rebuild a stock OEM block, you need to be sure that it’s worth rebuilding. Significant cracking around the main-bearing journals is often reason enough to pass on a block because it often cannot be fully repaired. Before you go through the entire machining and rebuilding process, do a thorough inspection of the block. After pressure washing the block, perform a Magnaflux test, which uses magnetic fields to seek out cracks in the metal.

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From the top of the block, you can see the locating pin in the deck and the proximity of the head bolt holes to the cylinder. W engines use six bolts per cylinder to ensure proper distribution of torque on the heads. The locating pin holds and aligns the heads in place during assembly.

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With the engine upside down on the stand, you can see the motor mounts, freeze pugs, oil plugs. The painted inside of the fuel pump boss allows the oil to return to the pan quicker, thus keeping a proper level and avoiding cavitation and oiling problems.

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On the underside of the driver’s side of the block, the oil filter adapter, oil-pressure fitting, motor mount, and freeze plugs have all been replaced with new parts. To build a strong and reliable engine, you commonly need to replace these parts.

Most engine shops advise customers to have a Magnaflux test performed on their blocks and other components. The Magnaflux procedure can reveal flaws in the surface structure of metals that are not normally visible to the naked eye. The system works by exposing the piece to be tested to a magnetic field. The piece is coated with a special iron oxide dye that works its way into any cracks or crevices. Using a black light, the dye is seen collecting at the points of cracks and imperfections.

The biggest benefit of Magnafluxing is finding problems before they happen and before money is spent on a bad piece of equipment or part. The reliability of Magnafluxing parts is such that it is often part of a regular maintenance program.

What to Check on W Blocks

The basics of inspection are similar for a stock rebuild, high-performance, or race build of a 348/409 block. Starting on the outside is a good way to begin, but keep in mind that most of the critical measurements are inside the block.

Do not take anything for granted when inspecting a 50-year-old block. An example is the condition of the outside of the block. It may look good for its age, but it may also conceal potential problems, and after some inspection and measurements, you may determine that it is not suitable for rebuilding.

As blocks were developed, their metal was shifted around in the casting procedure and ended up being thin in spots. Later, in order to make way for the bigger stroke and bore of the 409s, their water jackets also got thinner. On some 348s, and more so on 409s, the area just under the deck at the top of the block sides has been known to crack and needs to be thoroughly inspected for cracks.

On an engine that does not have a complete history, conditions may have been created to damage that part of the block. Also, with water jackets, the metal is sometimes rusted away from the inside. In the case of the Ws, it appears to be more of a case of thinner metal.

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At the bottom of the Bob Walla block, you see strong cylinder walls, cross webbing, and plenty of clearance for stroker engines. Note the final machining for items like oil pan holes, oil filter boss, and freeze plugs has not been done. At this point, it’s all about getting the block specs correct.

In addition, check for cracks in other high-stress areas of the engine, and this includes a close examination of the main journal webbing.

The W block’s freeze plugs are comparatively mild steel rather than the more durable cast iron of the block. Builders should assume the freeze plugs are rusting from the inside, unseen part side of the block. The freeze plugs found on a W engine are easy, relatively inexpensive one-time-use items and should be replaced. Opening up their holes in the block also helps in cleaning the block more effectively. Upon final block inspection, the bores of the freeze plugs should be thoroughly inspected.

There are three small plugs that look like freeze plugs that come with a 22-piece freeze plug kit. These three plugs are used for capping the oil galleries and are all installed on the front of the block. Two are near the galleries just outside the cam bore, and the remaining one is on the lower front of the block to the right of the crankshaft centerline.

(Video) Speedway Tech Talk - Aluminum Cylinder Heads for 348-409 Chevys

There are six other oil gallery plugs in a kit, and they are threaded to cap access holes to the oil galleries.

Inspection Process

Cleaning the block is essential to any engine work, and it starts prior to seeing just what condition the block is in. A good inspection, in turn, tells if the block is capable of the project intended. Any engine builder starts by taking off everything that is attached to the block including bolts, brackets, plugs, stuck lifters, and freeze plugs. With everything removed, a trip to a hot tank or industrial parts washer is the next step. It may take a few passes in various types of cleaner to remove years of accumulated grime, grease, oil, paint, and rust. (This process is explained in Chapter 10).

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W blocks, such as this Chevy 409, are hot commodities. While the 348 blocks are far more plentiful and less expensive, an original 409 block in rebuildable condition can sell for $5,000. When inspecting a used block, such as this, check the bolt holes and the entire deck surface for cracks. Fortunately, this one is not cracked.

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The spark plug location next to the exhaust made this a potential hot spot in the engine, but Chevrolet engineers added more holes for the coolant to pass through between the heads and engine block to remedy this design issue. This allows more coolant to be run around the bores.

Measure the Bores

The distinctive bores of the W engine should be measured and inspected. Also look to see if any ridges have built up. The factory bore sizes of the two engines are 4.125 inches for the 348 and 4.3125 inches for the 409. Use a telescoping micrometer to measure the bores of all eight cylinders, and measure each bore at the top, middle, and bottom to determine the overall condition of the bore. With its distinctive, slightly oval-shaped bore top, the edge of the bore should be checked for any damage or defects as should the bore itself. Only then can a realistic decision be made for any over- bore work.

There are always physical limits to overboring any block and the W blocks have theirs. When boring a W, the consensus of opinion is that .125 inch is the maximum. This measurement is safe, if the block has been sonically tested to ensure the material is there to machine. In most cases, if the bore is thinner at the bottom and thicker at the top, you can use the block if it is within a minimum of .125 inch. If the bore is thinner at the top, it often cannot handle the heat and expansion from the ignited fuel charge. Typically, boring out too much yields overheating to catastrophic block damage.

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Original 348 and 409 engines used this tube for a breather. Racers put on crankcase breathers on the valve covers, and eliminated it. The engines of that era required crankcase ventilation and often used the fill tube on the top front of the engine.

A good visual check of the distinctive W-engine relief cuts in the bores to determine compression is critical. These cuts must be free of burrs, sharp edges, and any other defect that could scrape the pistons or their rings and damage them. In the case of the piston rings, damage could cause oil to bypass the rings and work its way into the combustion chamber.

Inspect the Cam Tunnel

One internal area sometimes neglected in inspections is the camshaft bearing bores and surfaces. This is another area that is critical to not have any scrapes or sharp edges. If that area is damaged, it may damage the new cam bearings. Also, if the cam bed is worn excessively, it may need to be machined and trued.

In addition, there’s a correct and incorrect procedure for installing cam bearings for W engines, particularly the fifth cam bearing from the front. That bore has holes for oil travel and installing the bearing incorrectly blocks the oil route. When inspecting a W block, those holes should be free of constrictions. You also need to inspect the 16 lifter bores. They must be free of any cracks, damage, or restrictions to work properly.

Using a dial bore gauge micrometer, measure the cam tunnel journals. The measurement for the 348 is 1.868 inches and the measurement for the 409 is 1.869 inches.

Clear W-Block Bolt Holes

The W block’s threaded bolt holes must be clear of grime, dirt, or debris and have good threads that can hold a fastener properly. Inspect the threads for any damage or cross threading. Most of these holes hold bolts that need to be torqued to a particular specification, such as the heads and main bearing caps. The method is to first clean out the hole then “chase” the threads with a tap to make sure they work in the rebuild.

On a W engine, holes along the bottom of the sides of the block are connected to the oil galleries. It is important they be completely cleaned out and have good working threads for the plugs that will be installed upon rebuilding. Spend the necessary time to check out these holes— some of them are “through” holes and some are “blind” holes. These include deck and heads, timing chain cover, oil pan, fuel pump and oil filter bosses, main bearing caps, water pump, and engine mount holes.

One obscure W-engine hole is the small outlet that is often used for an oil-pressure sending unit. It is located on the outside of the block just above the oil filter mount at the rear of the block. Even if it is not used, it requires working threads to plug it.

Check Surface Trueness

A damaged or uneven surface mating area prevents gaskets from properly sealing, and therefore, your engine leaks. Hence, these mounting surfaces need to be flat and true, so your engine does not leak and performs at its best. These surfaces include the timing chain cover, oil pan, fuel pump boss, oil filter mount, the transmission mounting on the back of the block, and even the deck for the heads because these are gasketing surfaces and need to retain fluids, such as oil and water. Even the smaller flat areas, such as the water pump bosses and the part of the block that needs to match up to the intake manifold, need to be flat and smooth.

Chevy 348-409 Engine Block Guide (18)This Tech Tip is From the Full Book “HOW TO REBUILD & MODIFY CHEVY 348/409 ENGINES“. For a comprehensive guide on this entire subject you can visit this link:

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Chevy 348-409 Engine Block Guide (19)

At Walden Automotive, a 409 waits, along with its parts, for a rebuild. Like any serious build, it’s the selection of parts that ultimately makes or breaks the engine. Walden pushed the performance envelope and enlarged the bores to 4.600 inches and used a 4¾-inch crankshaft to push displacement up to 609 ci.

In the case of the intake mounting part of a W block, there are three holes each on the front and rear areas of this surface. Small holes that locate the intake gasket need to be clear of debris so use a rifling brush to clean them, and then the gasket can seat in them. The face of the deck and heads is critical as they need to match and be perfectly flat and level, so problems, such as head gasket failure, do not occur. Using a longer straight edge that can span the length of the block/head is a good way to check flatness. If these surfaces are warped, milling the heads or decking the block may be needed.

Block Preparation

Considering the age of the block and heads, and the conditions in which they operated, it’s quite likely they need a complete machining job, which includes align honing and boring the crankshaft, block decking, checking core shift, cylinder boring, and cylinder honing. Depending upon the condition, a number of these machining procedures may be required.

Align Honing and Boring

Align honing the crankshaft bore is one of the more common machining processes for blocks once you have measured your bores and have determined the amount of alignment. The honing tool trues the cap and main saddles in the block. It is different from align boring as less material is taken off the block in order to straighten the alignment of the main-bearing bores.

The crankshaft is the heaviest moving component in any block and as such, it can and does cause wear on the main-bearing mounts. Align honing restores the accuracy of a more precise fit of the crankshaft and its bearings in the main journals. Typically, align honing only takes off less than .003 inch of material compared to align boring, which can take off up to three times that amount.

As metal is taken off both the block and the main caps, both align honing and align boring should be done only when main-bearing saddles must be trued. Removing any metal from a block is a one-way process, and once done, cannot be undone. This isn’t a home shop operation, and you need to take the engine to a machine shop for a trained machinist to perform this procedure.

One option for align boring is milling the main caps down on the surface that meets the block. This gives the align honing/boring processes more metal to work with, and eliminates most of the need to hone or bore the block, thus saving the block. On the other side of the coin for boring the mains of a block, if a bigger crankshaft is used, boring is necessary to remove the excess metal.

Honing the bores from both ends of the block more effectively aligns the main bores, and this lessens bearing wear and ensures the removal of any low or high points in the bores. For most engine builds, align honing the block is the first machining operation and provides a core measurement from which others are referenced. Align honing should always be done with all main caps installed and even the oil pump housing mounted and properly torqued to replicate actual use. Honing, and how it takes the minimum of material off the block, helps to ensure the critical distance between the cam and crank- shaft centerlines that are important to the timing of the engine.

Another align hone/bore operation involves the cam tunnel. Usually, this operation is reserved for new blocks but can also be done if the block has suffered cam bearing damage or requires the use of a bigger diameter cam.

Block Decking

In this operation, a machinist mounts the block to a milling machine and trues the deck surface. Used blocks often have core shift in which the block moves and changes the straightness of the deck surface, among other areas. Milling the block’s deck brings it back into the correct plane, but it also reduces the deck’s surface so the heads are brought closer to the centerline of the crankshaft. The removal of the deck material usually generates a higher compression ratio in the block because the squish band area is decreased.

Such machining operations must be thoroughly planned—one of the results of milling is the piston traveling closer to the head, possibly impacting it if adjustments are not factored into the operation. In the case of milling to restore a true deck surface, oversize head gaskets and even shims can be used to ensure proper clearance between the pistons and the heads.

(Video) The reveal of the problems with the Chevy 348 in the 1958 Chevrolet Brookwood

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Here is a shot-blasted OEM W block getting its bores cleaned up on a Rottler boring center. These machines can be used for a surprisingly large number of operations on engine blocks today and can do everything from boring to threading all the holes in mere minutes on one machine. (Photo Courtesy Steve Magnante)

These methods are also used to control compression in W-engine builds and generally do not exceed .008 to .010 inch of removal. If decking is contemplated, call the piston manufacturer so they can compensate if needed.

Most milling machines are custom-made for machining blocks. The rate of feed has to be calculated for the material of the block as well as how much material is being taken off and the finish of the deck when it’s done. Gasket selection often matches the ending finish of a milled block. Cast iron is very hard, so the cutters on a milling machine must be very durable.

Checking for Core Shift

Most W-engine experts agree there is a significant amount of core shift in the 348 and 409 blocks. To check a block, take it to a machine shop to have it sonically tested. Testing all along the bores is the best way and results reveal the greater thicknesses at the top and bottom of the bores where they meet the bigger areas of the block. Testing should be done on all sides of the bores, not just one or two. Target wall thicknesses should be .200 to .300 inch at the top and bottom with a minimum of .100 to .115 inch anywhere else.

Cylinder Boring

Once your machine shop has completed the work on the mains and deck, most block machining operations include some kind of work on cylinder bores. Some cylinders require just honing to clean up the bore for a new finish or getting rid of any ridges; others require boring out the cylinder to use a bigger piston. A simple clean-up of the bores returns them to perfect roundness and removes any taper or built-up edges the cylinders may have developed during use.

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Here’s a Rottler boring center working on a block, cut- ting the relief bore into the block’s deck. Note how the block is located on a shaft that goes through the cam tunnel. Machine work like this is best left to the pros as an overbore is a series of boring operations from initial cutting to final finish. (Photo Courtesy Steve Magnante)

If an oversize bore is necessary or desired, a machinist uses a cylinder boring mill to complete the work. Overbores for W engines typically go .030 or .060 inch and increase the size of the engine, and as a result, compatible oversize pistons are required. A boring or torque plate is attached to the block much like a head would be and mimics the forces applied to the block when a head is mounted. This thick plate keeps the boring and later honing operations true to what conditions the block exhibits when assembled. Typically, boring is done to just less than the final size, usually .007 to .010 inch.

Cylinder Honing

Once the heavy machining of bore work has been done, cylinder honing finishes (“dresses”) the cylinders. Much like align honing, less metal is taken off during bore honing with the finish and final size being the primary targets. With specialized equipment, such as a cylinder hone, the finish of the bores can at the very least match and even surpass the original finish for consistency, accuracy, size, and roundness.

After the final honing process has been completed, the bore’s surface finish requires a consistent crosshatch pattern for better ring seating and oil control. One example is a brush finish that seals the piston rings faster.

Chevy 348-409 Engine Block Guide (22)This Tech Tip is From the Full Book “HOW TO REBUILD & MODIFY CHEVY 348/409 ENGINES“. For a comprehensive guide on this entire subject you can visit this link:

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Oiling System

Starting at the oil pickup in the bottom of the oil pan, the lifeblood of the engine is pumped via a gear-driven pump off the bottom of the distributor shaft. (The distributor is, in turn, run off a gear on its shaft that the cam turns.) The main oil gallery is fed off the full-flow oil filter to a main artery along the bottom of the driver’s side of the block. From there, it moves to two galleries to provide oil to the lifter galleries.

At the same time, there are supply routes in each of the main bearing web that feed the main bearings. They, in turn, via the holes in the crankshaft, feed the bearings of both the main and rod journals.

Also under oil pressure are the cam bearings and timing chain. Small holes in the rod caps allow oil to splash out of the rod journals onto the cylinder walls and that ends up on the wrist pins. Higher up in the block, the lifters are pumped with oil that is moved up the hollow push-rods to lubricate the rocker arms which, in turn, splash the valve- springs and their stems.

Holes in the floors of the heads and near other components lead the oil to drain back to the oil pan.

Typically, a W’s oiling system operates at about 35 psi. The oiling system in W blocks has always been very effective, and not much is needed in the way of modifications to it. Most engine builders drill and tap the openings of the pressed-in plugs on the front and rear of the block with 1/8- inch pipe threads for a more secure cap that can be removed if needed.

Aftermarket Manufacturers

Until recently, original blocks were the only option when building a 348 or 409. The growing interest in W engines has spawned an ever-increasing number of parts, and it was only a matter of time until new blocks hit the market. If a suitable, stock iron block cannot be found, you can select one of the aftermarket aluminum 409 blocks. Of course, if you build a W with more than 650 hp, you should opt for a high-performance aluminum block. While the aftermarket block can be built to stock or slightly modified specifications, these blocks are ideal for a street/strip or race build.

Bob Walla Racing

This company offers both aluminum and cast-iron blocks based on the 409 design. While the aluminum blocks are poured from 356 T6 aluminum, both blocks are modernized versions of the 409 block with reinforced webbing in the lifter valley, bellhousing mounting, and the main web areas.

The Bob Walla Racing (BWR) aluminum 409 bare block weighs approximately 140 pounds and the iron block weighs about 275 pounds. As far as bore size, the BWR aluminum block is capable of a 4.5-inch bore and the iron block, not using sleeves, can go up to 4.6 inches of bore.

The blocks from BWR have an incredible amount of versatility in the way they can be machined. The aluminum blocks are easily capable of a 572-ci build. By design the iron blocks, by their material nature and not requiring steel sleeves, are capable of going to 600-ci.

The aluminum blocks can be machined in both 409 and Chevy big-block architectures with a bigger main bearing, and in fact, the size increases from 2½ to 2¾ inches. This also allows the option of using something Chevrolet never offered on any W blocks–four-bolt mains. With this block, you can install 1045 billet steel caps, and therefore, the front and rear caps utilize two bolts and the center caps have four bolts for extra support. A bigger cam bore is also possible going up to 2.120 inches, the same size as a big-block Chevy.

Chevy 348-409 Engine Block Guide (23)

Bob Walla’s reproduction W iron block is an early version and will eventually be capable of hosting 609 ci. In addition, it will not need to be sleeved like aluminum blocks, so it will be much stronger than existing W blocks.

Chevy 348-409 Engine Block Guide (24)

The inside of the cast-aluminum pan shows a baffle welded in place to keep oil from moving away from the pickup. When the oil does not flow into the pickup, cavitation takes place and bearings can suffer damage, sometimes destroying the engine. Baffles keep the oil around the pickups.

Chevy 348-409 Engine Block Guide (25)

The Bob Walla aluminum W block has a 9.900-inch total deck height. It comes with four-bolt mains for all crankshaft journals. The front of the block shows how it has not yet been machined for items such as the holes for the timing chain cover, water pump, or brackets.

Chevy 348-409 Engine Block Guide (26)

(Video) 348 Chevy burning oil cylinder head problem found

The Bob Walla aluminum block has beefy reinforcement webs in the lifter valley, and therefore, it can support more than 1,000 hp for a build. The block is fitted with splayed four-bolt 1045 billet steel main caps, and it can use a big-block Chevy oil pan.

Chevy 348-409 Engine Block Guide (27)

This Bob Walla aluminum block fresh from casting is awaiting its machining cycles. The final production units were not completed as of the writing of this book. But from early indications, this engine will support up to 1,500 hp.

Chevy 348-409 Engine Block Guide (28)

Another view of the Walla aluminum casting. Even without machining, the bores have a slight oval shape to the tops of the bores, a W motor tradition. The Bob Walla Racing W blocks are very closely patterned after the original W motors rather than using Chevy big-block architecture.

Both BWR blocks are available with a .300-inch-taller deck, so the total deck height is brought to 9.900 inches, and that can support a healthy 4.5-inch stroke. To ensure clear running of any bigger stroker crankshafts, there is extra clearance in the oil pan rails. When configuring the 409 block as a big-block Chevy, the use of four-bolt, splayed 1045 billet steel main caps can be used with a big-block Chevy oil pan.

Internally, the blocks’ oiling system characteristics are based on Chevrolet’s using a grooved rear journal and priority oiling. Oil first goes to the main, rod, and cam bearings and then up to the lifters. To further assist with oiling, BWR blocks use Teflon-coated cam bearings. These blocks support a 348/409 or big-block Chevy-style starter. Matching the correct flywheel with the correct starter is the key here. Generally, an 11-inch flywheel is the standard. BWR moved one starter bolt hole to accommodate both small- or big-block Chevy.

The hole for the distributor is 409-correct and either a 409 or modified big-block Chevy distributor can be used. The difference is the shorter shaft length used on all W engines or the use of an adaptor or washer is required on these blocks. Elsewhere on the outside of the block, a 348/409 water pump is required, and that works with the extra volume of the water jackets in keeping the blocks cool.

World Products Merlin 409

The aftermarket block that has received the lion’s share of attention preceding its introduction has to be the World Products Merlin 409. It uses the Mark IV Chevy big-block architecture to overcome the inherent design problems of the original block. And with these design upgrades, the Merlin 409 block can support more than 1,000 hp, so these blocks are ideal for high-performance and race engines. This block, made from 357 T6 aluminum, the strongest available according to World, is safely capable of being a 509-ci engine, thus keeping the traditional “09” number intact but can go bigger depending on actual stroke used.

Chevy 348-409 Engine Block Guide (29)

A look from above of the World W block shows large ribs that add to the webbing structure that strengthens the block in the lifter galley. The webbing allows for more power to be created in the engine without splitting the block in half, which is a common occurrence on weaker blocks when they are exploited for more power. This stout block has a deck height of 9.600 inches, standard bore size of 4.240 inches, and it can be bored up to 4.530 inches. You can run up to a 4.250-inch crankshaft in it.

Chevy 348-409 Engine Block Guide (30)

When looking at the front of the World Merlin X aluminum Chevy 409 block, you may notice Chevy big-block similarities, and that’s because the basic architecture of that engine was used to create the World W block. The two share many similarities to begin with so the transition was logical. The Merlin X Chevy 409 features four-bolt main caps and a splayed setup, so this block supports many more horsepower than a stock block.

Chevy 348-409 Engine Block Guide (31)

This is the prototype of the World aluminum W block. Lamar Walden modified an existing aluminum World Merlin X Chevy big-block and created the first W-engine block for World Products. This block deck is far thicker than the OEM deck and therefore, it is much stronger for high horsepower levels. The location of the ports for the water pump and the angle of the block’s decks were the major changes. These were redesigned to match the architecture of the W motor.

Chevy 348-409 Engine Block Guide (32)

Here’s a close up of a rare piece of 348/409 history. This is the first prototype aluminum 409 block made by Lamar Walden with World Products. Notice its serial number, machined into the face of the block.

Chevy 348-409 Engine Block Guide (33)

For a high-performance application, the Lamar Walden two-piece billet aluminum timing chain cover is an excellent upgrade, but it definitely has a non-stock appearance. It uses a standard 409 or big-block Chevy gasket.

Chevy 348-409 Engine Block Guide (34)

This front view of the World block shows the traditional 348/409 water pump bosses, but the timing chain cover pattern is that of a big-block Chevy. Building such an engine allows the use of many big-block Chevy parts and big-block Chevy specs, such as the distance between crankshaft and cam.

Developed by Lamar Walden, the block is based on the Chevy big-block World Merlin X block. The distance between the cam and crankshaft centerlines is a Chevy big-block spec. When Walden created the Merlin 409, the deck angle was changed to the 348/409’s 74 degrees, and the water pump inlet bosses moved out- ward on the face of the block to fit a stock or aftermarket 348/409 water pump. The 409 block uses big-block internals, such as cam size, crankshaft, timing chain, and rods; and the outside of the block uses a big-block timing chain cover and starter. World and Walden modified the block to accept 348/409 heads, and the block was announced on the heels of Edelbrock’s popular aluminum 409 heads.

World’s aluminum block is capable of a 4.560-inch cylinder bore and utilizing a standard big-block Chevy crankshaft with up to 4.250 inches of stroke. The design of the Merlin 409 block offers Chevy-based priority main oiling, extra-thick walls, blind bolt holes to prevent leaks, expanded water jackets, and a reinforced bellhousing mounting area. Other features include replaceable ductile iron cylinder sleeves, main caps located by ring dowels, and ARP hardware.

One of the first things you notice is the strong webbing spanning the lifter galley. Hefty reinforcement ribs promote a stable upper block while tying into the main areas that can now offer something Chevrolet never did, splayed four-bolt main caps. Inside, big-block Chevy pistons with 348/409- style domes are used.

Written by John Carollo and Posted with Permission of CarTechBooks


Chevy 348-409 Engine Block Guide (35)

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