Rotating Assembly Interchange for Small-Block Ford Engines

What you use in your engine’s bottom end depends on how you intend to use the engine. If you’re going racing, that’s one thing. And if you’re building a daily driver or boulevard cruiser, that’s quite another. The 221/260/289 all share the same bottom-end components with a 2.870-inch stroke. Main-journal size is 2.249 inches. These engines differ in bore size, but all use the same 1M crankshaft and 5.1545-inch C3AE connecting rods. Piston and bore size are relative to displacement at 3.500, 3.800, and 4.000 inches respectively (221/260/289 ci). After the small-block Ford evolved to a 4.000- inch bore to get 289 ci, further growth was with increased stroke. The 302 was increased to 3.000-inch stroke in 1968 via a new 2M crankshaft and shorter 5.090- inch C8OE connecting rods.

The 351-ci Windsor arrived for 1969 featuring a new block with a taller deck to get 3.500 inches of stroke. It had a 3M crankshaft and 5.956-inch C9OE connecting rods with the same 4.000-inch bore as the 289/302. Main journal size on the 351W was larger at 3.000 inches.

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The Boss 302 has the same 4.000-inch bore and 3.000-inch stroke as a 302. The difference is a Boss 302-specific steel crankshaft with what is basically the 289’s 5.1545-inch C3AE connecting rod with 3/8-inch bolts. Main-journal size is the same as you find in the 221/260/ 289/302 at 2.249 inches. The 289 High Performance connecting rod and Boss 302 rod are basically the same forging except for the 302’s spot-faced 3/8-inch bolts and more metal at the large end to accommodate these bolts. The Boss 302 has a different piston than a 289 to achieve 302 ci. The piston has a high dome and works with the Boss 302’s canted-valve 351C cylinder head by matching the chamber and increasing compression.

There’s also a hard-to-find Boss 302 Trans Am rod available with cap-screw bolts: the C9ZE-G rod, which is on a par with the Crower Sportsman rod widely available. If you’re building a Boss 302 to go vintage racing, you don’t need to spend a fortune on a set of C9ZE-G cap-screw rods when the aftermarket offers a wealth of more-affordable hardware for Boss 302 and 289 High Performance engines.



The 351C, 351M, and 400M engines are close cousins of the 221/260/289/ 302/351W engines in that they have the same bore spacing, but 335-series engines employ a completely different block where very little interchange is possible. The 351C has larger 2.740-inch main bearing journals than the 221/260/ 289/302, yet smaller than the 351W and 351/400M. It also has a 351C-specific connecting rod: the D0AZ-A (standard), or the D1ZZ-A (shotpeened and Magnafluxed for Boss 351 and 351 highoutput), which is 5.780 inches in length. The 351M and 400M engines have the same main-journal size as the 351W (3.000 inches), with larger counterweights that do not clear a 351W block.

Understanding 351C, 351M, and 400M rotating/reciprocating stock is quite simple. The 351C 4M crankshaft, connecting rods, and pistons fit this engine only because main journal sizing and rod length is unique to the 351C. These components do not interchange with anything else, including 351M/400M. The taller-deck 400M V-8 uses a 5M nodular iron crankshaft with a longer 4.000-inch stroke, making it the longest stroke of any Ford V-8 at the time. The 400M’s 4.000-inch stroke is what made it a powerhouse for full-size luxury cars and pickup trucks in the 1970s.

To control manufacturing costs, Ford ended 351C production in 1974, offering buyers the 351M engine for 1975. It was the 400M de-stroked to 351 ci with a 3.500-inch-stroke 1K crank, 3.000-inch main journals, and the same D1AZ-A 6.580-inch connecting rods. There’s little point in building a 351M when you can have 400 ci with the same amount of weight. Think of the 400M as a 351M stroker, where you get to maximize displacement for dollar spent. And although you think of the 351/400M as a small-block, Ford thought of it as a big-block replacement for the FE-Series 390 and 428.



Every bit of engine power passes through the crankshaft on its way to the tires. In high performance applications, higher quality crankshaft material and manufacturing methods make for stronger components. Everything you should need to know about choosing and spotting the best-possible crankshaft follows.



All 221, 260, and 289 engines used the same basic 1M cast-iron crankshaft with a 2.870-inch stroke and 2.249-inch main journals. The 1M crank isn’t as widely available as it used to be. Although it is easy to assume the 289 High Performance V-8 had a steel crankshaft or some kind of special nodular-iron crank, it had the same cast-iron crank found in the 221, 260, and 289 engines with one exception: Brinell hardness testing and the appropriate Brinell test mark on the crankshaft. This didn’t necessarily make a 289 High Performance crank a better piece, but verified its integrity. The 289 High Performance V-8 had a handpicked cast-iron crankshaft, which was tested for hardness. Another difference is the Hi- Po’s slide-on steel plate counterweight used to counter the additional weight created by larger 3/8-inch rod bolts.

The 221/ 260/ 289 crankshaft is identified by the 1M cast into the first counterweight/ journal. A 289 High Performance crankshaft is identified the same way, plus the Brinell test stamp I’ve mentioned. Sometimes there’s a “K” nearby on the Hi- Po crankshaft, but not always. When you’re shopping for a crankshaft, be sure you haven’t found a bogus Hi-Po crank with a fake Brinell test mark. They’re out there waiting for unsuspecting buyers. And besides, you don’t have to use a Brinell tested 1M crankshaft in a 289 High Performance engine when Magnafluxing and hardness testing are available at most reputable machine shops.



The 302 cast-iron crankshaft with a 3.000-inch stroke and 2.249-inch main journals is identified by a 2M on the first counterweight/journal. It is not interchangeable with 221, 260, or 289 rods, unless you’re planning to use a custom piston, because it uses a shorter 5.090- inch connecting rod.

Later on in the 302’s production life, Ford made changes to the 2M crankshaft to improve fuel economy and reliability. Other changes came of environmental law and plant closings. Crankshaft production shifted from Ford’s North American foundries around Detroit, which were shut down, to those in Canada across the Detroit River in Windsor. You must be mindful of these changes when you’re shopping for a 302 crankshaft. The most rugged 2M 302 crankshaft you can get is what Ford used in 5.0L High Output V-8s from 1982 to 2000.


Rotating Assembly Interchange for Small-Block Ford Engines 1

All 221/260/289/302/351W cranks are marked for identification purposes. This is a 1M cast-iron crankshaft with 2.870-inch stroke for the 221/260/ 289-ci engines.

Rotating Assembly Interchange for Small-Block Ford Engines 2

Here’s the 1M package with 2.870- inch stroke with C3AE connecting rod forging.

When 302/5.0L crankshaft manufacture shifted to Canada, these cranks got better, which is one reason why the 5.0L High Output engine is so durable and dependable. You can thrash on these engines hard and they just keep coming back for more. In your search for a good 5.0L 2MA crankshaft, don’t mistakenly pick up one for the 255-ci (4.2-liter) engine. It looks the same externally with the same 3.000-inch stroke but has hollow rod journals for reduced weight, which also compromises strength and makes the balancing process more involved.



The 351 Windsor’s cast-iron crankshaft has a 3.500-inch stroke with 3.000- inch main journals and a 3M in the forward-most counterweight/journal. A forged steel crankshaft was never factory installed in the 351W. And Ford’s 351W crankshaft story is much the same as I just told you with the 302 2M crankshaft. The 3M cranks are extremely durable and can take a lot of punishment given ample oil supply and common sense engine tuning.


Rotating Assembly Interchange for Small-Block Ford Engines 3

This is the large end of the 289 High Performance C3AE connecting rod. The only difference between the Hi-Po rod and a standard 221/260/289 rod is larger 3/8-inch rod bolts. Standard rods had a 5/16-inch bolt. You can improve the standard rod with an ARP 5/16-inch bolt, which is much stronger.

Rotating Assembly Interchange for Small-Block Ford Engines 4

The 289 High Performance 1M crankshaft not only received Brinell hardness testing, it had to have a slide-on stamped-steel counterweight to add mass in front to counter heavier 3/8-inch rods bolts.

Boss 302

The 1969–1970 Boss 302 engine was the only small-block Ford ever to get a forged-steel crankshaft from the factory. Boss 302 had a 3.000-inch stroke and 2.249-inch main journals from the factory identified by “D0ZE-A” or “7FE-8” on the forward-most counterweight/journal. Only 1969 Boss 302 crankshafts had cross-drilled oil passages. If you need a DOZE-A/7FE-8 steel crankshaft for your Boss 302 engine, good luck because they’re scarce and darned expensive should you find one. Aftermarket crank grinders like Eagle, Scat, and Probe Industries manufacture forged steel crankshafts with 3.000-inch stroke for the Boss 302, which works well for less money than a factory crank and only you know it’s there. Remember if you go with one of these aftermarket steel cranks, most are designed for a one-piece seal, which means you have to machine your Boss block for the one-piece seal. Again, no one knows it’s there, and rear main seal leaks become a thing of your past.


Rotating Assembly Interchange for Small-Block Ford Engines 5

This is a 351W crankshaft with 3.500- inch stroke, 3.000-inch mains, and a 3M mark for identification.


The 335-Series engine family uses a nodular iron crankshaft in all applications. Ford never installed a steel crank in any 335-series engine—not even the Boss 351 and 351 High Output, which had Brinell hardness testing. Standard 351C crankshafts have 4M cast into the forward most counterweight/journal. Boss 351 (1971) and 351 high-output (1972) cranks had 4MA cast into the forwardmost counterweight/journal along with a Brinell test mark.


Rotating Assembly Interchange for Small-Block Ford Engines 6

Although the 351C has the same 3.500-inch stroke as the 351W, it employs a different 4M crankshaft with 2.749-inch main journals.



Because the 400M was equipped with a 5M crankshaft with 3.000-inch main journals, it is not interchangeable into the 351C, which has smaller 2.740-inch main journals. The de-stroked 351M has a 1K nodular-iron crankshaft with 3.500- inch stroke and the 400’s 3.000-inch main journals. It can easily be identified by its smaller counterweights.


Ford Racing Crankshafts

Much has changed at Ford since we first published this book in 1998. Ford Motorsport SVO is now Ford Racing Performance Parts, with a substantially different product line. I’m discussing old and new parts because both are out there. Ford Racing Performance Parts has stopped doing small-block crankshafts, connecting rods, and stroker kits. However, there are a lot of Ford Motorsport SVO crankshafts and connecting rods available used and sometimes still in their factory packaging. These cranks are covered in the accompanying sidebar.


Rotating Assembly Interchange for Small-Block Ford Engines 7

Side by side are two types of small-block Ford crankshafts. On top is a latemodel 302/5.0L 2MA crankshaft designed for one-piece seal. Bottom is a 1M crankshaft with a rear mail seal lip designed for a two-piece seal. Note the differences in these two castings in terms of counterweights and journals.

The good news is there are many crankshafts out there from when Ford Motorsport SVO was doing them. These cranks are machined from AMS 6415 raw steel forgings, making them indestructible if you know how to put an engine together properly. This means using highspeed oiling systems, precision-ground rod and main journals, and large-fillet radii. Some 351W cranks have knifeedged counterweights and pin-lightening holes. Journals are polished and nitratehardened. These modifications reduce friction and corresponding heat. The 351W journals are machined to accept 0.940-inch-wide steel connecting rods.

If your game plan is to increase displacement, there are stroker kits out there from not just the old Ford Motorsport SVO program, but from reputable companies like Scat Enterprises, Eagle, and Probe Industries. Some of these kits enable you to take a 302 to 347 ci or a 351W or 351C to as high as 427 ci.


Crankshaft Modifications

Crankshaft modifications are universal for all types of engines, and the smallblock Ford is no exception. The objective is to improve oil flow and control to main and rod bearings. You should chamfer the oil holes to improve flow. It is always a good idea to Tuffride a crankshaft to ensure durability. While addressing durability, always think about dynamic balancing. If your small-block will be running a lot of accessories, include the crankshaft pulley in your balancing program. Check the pulley for runout and other flaws before balancing.

While grinding a crankshaft, it’s important to limit undersize to .020 inch maximum. While it may not seem like much, but, for each .010 inch you go undersize, you compromise the crank’s integrity. If you have to go beyond .020- inch undersize, find another crankshaft.


Connecting Rods

Small-block Ford V-8s are blessed with rock-solid integrity right from the factory. Ford never spared anything when it came to engineering; hence all the revisions over an engine’s production life. The 221, 260, 289, and 302 engines enjoy strong forged-steel connecting rods, which changed little in their 38 years of production. The 289 High Performance connecting rod is the same forging as the standard 289’s, with the exception of larger 3/8-inch rod bolts mashed into a broached seat. Larger 3/8-inch bolts provide the integrity needed for high RPM use. And when you recondition standard 289 rods, you have a choice between 5/16- or 3/8-inch ARP rod bolts.

The 221/260/289 rod is a 5.1545- inch (center-to-center) C3AE forging, while the 302’s is a shorter 5.090-inch C8OE rod as a means to quick identification. What may baffle you is the Boss 302 rod, which is the same 5.1545-inch C3AE forging used in the 221/260/289 engines with the exception of having 3/8-inch broached rod bolts. The C3AE rod is a pinch longer than a C8OE 302 rod, offering more dwell time. I’m not sure why Ford elected to use this rod instead of a C8OE 302 rod. The C3AE Boss 302 rod was also used in 2.3L overhead-cam turbo fours used in the Mustang SVO, Mustang GT Turbo, Capri RS Turbo, Thunderbird Turbo Coupe, and Cougar XR-7 Turbo during the 1980s.


Rotating Assembly Interchange for Small-Block Ford Engines 8

This is the C3AE rod forging for 221, 260, 289 engines. Early C3AE forgings have an oil splash hole, which was deleted as a running production change.

Rotating Assembly Interchange for Small-Block Ford Engines 9

The Crower Sportsman connecting rod for small-block Fords is an excellent choice if you’re planning weekend racing. This is an affordably priced connecting rod for any budget project.

Because the 302 has different bottomend stroke dimensions than the 221/260/289, it has a different rod—a C8OE forging (C8OZ-A part number). This rod forging is also common to 5.0L high-output engines. Aside from subtle changes to this rod forging at the large end (thicker rod cap) to make it stronger for high-performance use, it is virtually the same rod. Always opt for a matched set of rods when you find them. One basic modification you should make to both the C3AE and C8OE rods is an upgrade to 3/8-inch ARP bolts for improved durability. Make sure you have plenty of material around these bolts when this modification is made. Closely inspect each rod before pressing it into use.

The same can be said for the 351W C9OE connecting rod forging, which came from the factory with 3/8-inch bolts. This is a good strong rod from the factory. All you need to do with this rod is fit it with ARP bolts to improve durability. I also suggest Magnafluxing and shot peening for maximum durability.

Ford built the 351C for increased performance from the beginning. As a result, it has a super-durable D0AE-A connecting rod with 3/8-inch bolts. All you have to do is recondition them with Magnafluxing, shot peening, and ARP bolts. The Boss 351 and 351 High Output have a special D1ZX-AA connecting rod, which was Magnafluxed and shot peened from the factory for added strength. The 400M and de-stroked 351M have a D1AZ-A rod, which was used throughout their entire production life.


Ford Motorsport SVO

When this book was first published in 1998, Ford Motorsport SVO (now Ford Racing Performance Parts) offered a variety of connecting rods for small-block Fords. Such is not the case today. Ford Racing Performance Parts has gotten away from bottom-end performance components because the market is extremely competitive. However, there are plenty of used and new-old-stock Ford Motorsport SVO bottom end parts out there. The aftermarket also offers a wealth of engine kits that work well for your project. The Crower Sportsman connecting rod, as just one example, is an affordable, yet outstanding connecting rod for small-block Fords because it is more rod than you ever need for a street or weekend bracket racing engine. Because this book’s focus isn’t aftermarket parts, I focus more on what’s available from Ford.

The Ford Motorsport SVO M-6200- B351 “cracked” connecting rod was made from the latest technology available at the time when it was introduced in the late 1990s. With a center-to-center of 6.120 inches, this is an exceptional connecting rod for a small-block Ford build. The small end is bronze bushed and machined for a .912-inch pin. The big end is set up for a 351W at 2.310 inches. For added reliability, you can fit this rod with the M-6214-B351 bolt or an equivalent from ARP. Four other highperformance connecting rods were available from Ford Motorsport SVO for small-block Fords. If you go out there and cruise the Internet searching for Ford Motorsport SVO connecting rods, there are plenty of choices out there, especially on eBay and speed-equipment websites.



It has been a long time since you could buy original-equipment factory pistons for small-block Fords. But, unless it is important to you to have NOS pistons, the aftermarket offers cast, hypereutectic, and forged pistons in all shapes and sizes for small-block Fords. What type of piston you use depends on your engine’s mission. Cast and hypereutectic pistons are your best bet for street use; even a stock 289 High Performance V-8 can get by with these. Flat-top pistons in a Hi-Po net you 10.0:1 compression, depending upon compression height. But 10.0:1 can be risky, depending on your cam profile. If you desire compression around 9.0:1 in order to keep things safer, opt for dished Speed-Pro pistons available in cast or hypereutectic in standard, 4.020-, 4.030-, or 4.040-inch bore sizes. And remember: As you increase bore size, you increase compression.


Rotating Assembly Interchange for Small-Block Ford Engines 10

This is a hypereutectic flat-top piston for 289/302 with valve reliefs.

Rotating Assembly Interchange for Small-Block Ford Engines 11

This is a Federal-Mogul hypereutectic flat-top piston for 289/302. Piston oversize is normally inscribed into the piston crown.

Rotating Assembly Interchange for Small-Block Ford Engines 12

These are dished flat-top cast pistons in a 289 short-block.

Rotating Assembly Interchange for Small-Block Ford Engines 13

Boss 302/351C piston at top dead center. Notice the high dome for 11.0:1 compression.

Rotating Assembly Interchange for Small-Block Ford Engines 14

This is a 351C-2V forged piston with valve reliefs.

Rotating Assembly Interchange for Small-Block Ford Engines 15

Two 157-tooth flexplates for smallblock Fords. On the left is a 28-ounce offset flexplate for a 1962–1981 221/260/289/302 small-block. On the right is a 50-ounce offset flexplate for a 1982+ 5.0L High Output small-block. It is very important to get this right. Note the difference in weight size here. Smallblock Fords are externally balanced, which means you must get this right or face serious vibration issues.

What piston material you use depends on how you’re going to use your engine. Cast and hypereutectic pistons have a more conservative expansion rate, which makes them ideal for street use. Tolerances can be tighter without concern for excessive expansion. Forged pistons are more appropriate for racing and especially for those who intend to use nitrous, supercharging, or turbocharging. Forged pistons, however, have a much greater rate of expansion, which calls for looser tolerances. This could mean excessive piston noise (skirt slap) during cold startups. A common rule is to use press-fit piston pins on cast and hypereutectic and floating pins on forged pistons. In any case, it’s a matter of personal preference.

Ford utilized two basic ways to control compression ratio in small-block Fords: combustion chamber size and piston dome configuration. Most of the time, compression was controlled by the amount of dish, if any, in a piston. The 221, 260, 289, 302, and 351W had their compression controlled by the amount of piston dish. Flat-top pistons were good for higher compression, especially with 52- to 57-cc wedge chambers. Ford used dished pistons to reduce compression.

Compression depended upon how much dish volume there was. In 1968, combustion chambers got larger and gained more of a shovel shape, which helped reduce compression and corresponding emission levels. In all cases except the 351C, 351M/400M, pistons had valve reliefs.


Flywheels and Flexplates

For the small-block Ford’s production life, which spanned nearly four decades, there were a lot of flywheels and flexplates. Careful selection is important because, as most of you know, Ford had many variations. Choose the incorrect flywheel or flexplate and you may have problems with starter engagement, torque converter/clutch fitment, or a balance issue and unwanted vibration. All 221, 260, 289, and 302 engines prior to 1982 had 28-ounce offset balance, which means you need a 28-ounce offset balance flywheel or flexplate before you go to dynamic balancing. From 1982 on, 5.0L engines must have a 50-ounce offset balance flywheel or flexplate. The same can be said for harmonic balancers, which must also be the corresponding 28- or 50-ounce offset balance.


Rotating Assembly Interchange for Small-Block Ford Engines 16

This is the narrow C4AE-6316-C or D harmonic balancer for 289 engines prior to 1968. The C4OE-6316-A balancer for 221 and 260 looks identical at first glance.

Rotating Assembly Interchange for Small-Block Ford Engines 17

For 1968, the 289/302 received a wider harmonic balancer and bolt-on stamped-steel timing pointer.

Rotating Assembly Interchange for Small-Block Ford Engines 18

The 289 High Performance V-8 was fitted with a much wider harmonic balancer to compensate for heavier connecting rods (due to larger 3/8-inch bolts). This balancer is similar to 1969–1970 Boss 302.

Rotating Assembly Interchange for Small-Block Ford Engines 19

Here’s the 351C/351M/400M balancer with right-hand bolt-on timing pointer. All were right-hand pointers due to left-hand water pump inlet.

Rotating Assembly Interchange for Small-Block Ford Engines 20

Two small-block Ford harmonic balancers side by side. On the left is an early 289/302 balancer with 28-ounce offset balance. On the right is a late-model 5.0L High Output balancer with 50-ounce offset.

Harmonic Balancers

As with flywheels and flexplates, proper selection of a harmonic balancer and even the accessory drive crank pulley is crucial to smooth operation. If you’re going with a large accessory drive pulley, proper selection is critical to balance, believe it or not. Pulley runout must be checked first. Ideally, you balance this pulley right along with the harmonic balancer and flywheel/flexplate because all small-block Fords are externally balanced.

The 221, 260, and 289 dimensionally share the same basic harmonic balancer with a 28-ounce offset balance. However, the 289’s balancer is different from a part-number standpoint. The 221 and 260 employ a C4OE-6316-A balancer versus the C4AE-6316-C or D balancer common to the 289. Both balancers are 1 inch in width and 63⁄8 inches in diameter.

The 289 High Performance balancer is much wider (337⁄64 inches) and is easy to identify. It is wider and heavier to compensate for the high revs and larger/heavier 3/8-inch rod bolts. A similar story exists for the 1969–1970 Boss 302 balancer, which is also wider.

Written by George Reid and Republished with Permission of CarTech Inc





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