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Rotating Assembly Parts Interchange for Small-Block Ford

Your small-block’s master plan depends on how you intend to use the engine. If you’re going racing, special attention is required along with heavy-duty aftermarket parts and building technique. If you’re building a daily driver or boule-vard cruiser, you can save money by choosing only what you need. Too many street enthusiasts overkill with expensive high-end aftermarket parts when proper selection and preparation of Ford parts get the job done for less money. Your first line of defense is knowledge of small-block Ford rotating parts and what works best.


This Tech Tip is From the Full Book, FORD SMALL BLOCK PARTS INTERCHANGE. For a comprehensive guide on this entire subject you can visit this link:


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Ford’s reputation for engineering redundancies cannot be over-estimated. Ford factory parts never remained the same because Ford engineers never rested. These parts are usually better (or worse in some cases) with time. Weaknesses were unearthed and eliminated either in hard-core testing, on the racetrack, or from consumer/dealer feedback. You will find a wide variety of Ford castings and forgings for your small-block.

Choosing the right part means knowing something about how these parts have evolved over time plus eliminating the various myths that go with each of them.



The 221, 260, and 289 engines employ the same basic “1M” castiron 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 some believe the 289 High Performance V-8 had a steel crankshaft or some kind of special nodular iron crank, it actually had the same “1M” cast crank found in the 221, 260, and 289 engines with one exception, Brinell hardness testing. This didn’t make a 289 High Performance crankshaft a better piece, but instead verified its integrity. Also, the Hi-Po’s slide-on steel plate counterweight was used to balance the additional weight of larger 3/8-inch rod bolts.

The 221, 260, and 289 crankshaft is identified by “1M” cast into the first counterweight/journal. A 289 High Performance crankshaft is identified the same way plus having the Brinell test stamp. Sometimes, you find a “K” 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. You don’t have to use a Brinell-tested “1M” crankshaft; Magnafluxing and hardness testing are available via most reputable machine shops. Another form of identification is orange or yellow paint markings on the 289 Hi-Po’s crankshaft counterweights.

The 302 castiron 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 use a custom piston because it employs a slightly shorter (5.090-inch) connecting rod.


The bones of Ford’s 221/260/289 with the cast/nodular  iron “1M” crank- shaft and C3AE  5.1545-inch  rod forging. You have a choice of cast, hypereutectic, or forged pistons depending on how you’re going to use your small-block Ford. (Hypereutectic is a high-silicon cast piston with added strength, which is a nice compromise between forged and cast.) A street-driven restoration does not need a forged or even a hypereutectic piston. 


There are two basic C3AE connecting rods. Early C3AE rods (right) have oil holes for cylinder wall lubrication. Ford deemed this unnecessary, deleting the oil hole in production (left). All your connecting rods must be the same style (all with oil holes or all without oil holes) in the interest of dynamic balance and uniformity.



C3AE and C8OE rods are durable forgings. Shot peen and recondition them, and fit them with ARP bolts so they’re as good as new. What you do with them depends on how you intend to use the vehicle. If you’re going racing, a good aftermarket I- or H-beam rod is the best choice. 


The cast “1M” cast/nodular iron crankshaft is common to the 221/260/289 family with a 2.870-inch stroke, 2.749-inch main journals, and 2.311-inch rod journals. Ford did not offer a steel crank for the 221/260/289. The 289 High Performance V-8 received hardness-tested “1M” cast cranks. 


The crankshaft oil slinger splashes lubrication and keeps heavier amounts of oil away from the crankshaft’s front seal. If you’re going with dual-roller timing chain, this slinger must be deleted because it can interfere with the chain, doing major engine damage.


The 289 High Performance V-8’s crankshaft has this additional stamped steel counterweight, which compensates for the heavier reciprocating mass. The 289 High Performance V-8 has larger 3/8-inch rod bolts, which adds reciprocating weight. 


Here’s the 1963–1967 289 High Performance slide-on crankshaft counterweight. The Hi-Po needs a nar-rower timing sprocket and chain to make room for this counterweight. 


Here are two small-block Ford nodular iron crank-shafts. On the left is a “2ME” crank for the 5.0L engine with a one-piece rear main seal. Notice the absence of a seal lip. The 302 “2M” crank on the right has a seal lip for the two-piece rear main seal, which was common prior to December 1982. Also remember that there is a 28-ounce offset balance prior to 1982 and a 50-ounce offset from 1982-up. 


Later in 302 production, in the 1980s, Ford made changes to the “2M” crankshaft to improve fuel economy via weight reduction, a lighter crank-shaft. Other changes came because of environmental laws 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 should be mindful of these changes when you’re shopping for a 302 crankshaft. The most rugged “2M” 302 crank-shaft was used by Ford in 5.0L High Output V-8s from 1982 to 2000. It can be identified by “2MA” or “2ME” markings. It is clearly a different crank than earlier “2M” castings.

When 302 crankshaft manufacture shifted to Canada, these cranks actually became stronger, which is one reason that the 5.0L High Out-put engine is so rugged 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” or “2ME” crankshaft, don’t mistakenly buy one for the 255-ci (4.2L) engine, which looks the same externally with the same 3.000-inch stroke, but has hollow rod journals for reduced weight, which also compromises strength. The 255 crankshaft is approximately 9 pounds lighter than the 302 crank. The 255 crank tips the scales at 35 pounds, considerably lighter than the 44-pound 302 crank. For some, the 255 crank is very effective performance-wise due to its reduced weight. However, you can also wind up with a broken crank-shaft, which means that if you use the 255 crank you take your chances. Some racers have used the 255 crank with great success, however risky. 


Connecting Rods: 221/260/289/302

Ford didn’t spare much when it came to engineering, hence all the revisions over the small-block Ford V-8’s production life. The 221, 260, 289, and 302 engines employ strong forged steel connecting rods, which experienced very few changes over their long production life. The 289 High Performance connecting rod is the same C3AE forging as the standard 289 with the exception of the larger broached-head 3/8-inch rod bolts being pressed into a broached seat. Larger 3/8-inch bolts provide the integrity needed for high-RPM use. When you recondition standard 289 rods, you have a choice of 5/16- or 3/8-inch ARP rod bolts. Go with 3/8-inch ARP bolts and shot-peened C3AE rods for strength and durability.


This 5.0L (302-ci) nodular iron “2ME” crankshaft has a 50-ounce offset balance. Probably the quickest way to identify this crank (aside from the “2ME”) is the balance bosses located throughout the crank. 


Here’s a 289 High Performance crankshaft with orange paint markings. Although you should look for the Brinell test mark, which means the crank has been tested for hardness, this mark is difficult to see and is little more than a small dent. These cranks were dabbed with orange paint at the factory for quick identification. Hi-Po rods received 3/8-inch broached bolts and an orange or yellow paint mark.


Both of these connecting rods are C3AE forgings. On the left is the Hi-Po/Boss 302 forging machined for broached 3/8-inch bolts. On the right is the C3AE-D rod with the cylinder wall oil hole and standard 5/16-inch bolt holes. 


The 289 High Performance/Boss 302 rod (left) has been machined for a broached 3/8-inch bolt. The standard 221/260/289 rod (right) has been sized for a 5/16-inch bolt. Aside from using larger rod bolts, the Hi-Po/Boss rod is the same C3AE forging as standard. 


Three small-block Ford connecting rods from left to right: C3AE rod for the 221/260/289, C8OE rod for the 302, and C3AE 289 Hi-Po/Boss 302 rod with 3/8-inch broached bolts. If you recondition and shot peen a C3AE rod and fit it with 3/8-inch ARP bolts, you have the equivalent of a 289 High Performance or Boss 302 rod. Aside from machining differences, the C3AE rod forging is the same.


Small-block crankshafts received Ford casting numbers later in the 1980s. This is a 351W crankshaft (E4AE-BA) with the one-piece seal. It can also be identified by a “7M” or “7MA.” The 351W crank has a 3.500-inch stroke with 3.000-inch mains and 2.311-inch-diameter rod journals. 


The 221/260/289 rod is a 5.1545-inch (center-to-center) C3AE forging; the 302 has a shorter, 5.090-inch, C8OE rod. You may be baffled by the Boss 302 rod, which is the same 5.1545-inch C3AE forging used in the 221/260/289 engines except for 3/8-inch broached rod bolts. The C3AE rod is slightly longer than a C8OE 302 rod, offering increased piston dwell time. It is not known why Ford used this rod instead of a C8OE 302 rod in the Boss 302 engine. 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.

Because the 302 has longer stroke dimensions than the 221/260/289, it also has a different C8OE rod forging. This shorter rod forging is also common to 5.0L High Output engines. Aside from subtle changes to this rod 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 for balance and consistency.

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 before making this modification. Closely inspect each rod before pressing it into use.


Boss 302

The Boss 302 has the same 4.000-inch bore and 3.000-inch stroke as the 302 except it has a Boss 302-specific forged steel crank-shaft with what is basically the 289’s 5.1545-inch C3AE connecting rod with 3/8-inch bolts. The main journal size is the same as you find in the 221/260/289/302, 2.249 inches. The 289 High Performance connecting rod and Boss 302 rod are the same forging. The Boss 302 has a different piston than a 289 to achieve 302 ci and work with the Boss 302’s poly-angle-valve 351C cylinder head with a high dome chamber match.

There’s also a hard-to-find Boss 302 Trans Am rod available with cap-screw bolts and the C9ZE-G rod, which is on 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 because the aftermarket offers a wealth of more affordable hardware for Boss 302 and 289 High Performance engines.


Flywheels and Flexplates: 221/260/289/302/Boss 302

Throughout the small-block Ford’s production life, which spanned nearly four decades, many flywheels and flexplates were available for different applications. Careful selection is important to success. Choose the incorrect flywheel or flexplate and you may have problems with starter engagement or torque converter/clutch fitment, or find yourself with a balance issue and unwanted vibration.

All 221, 260, 289, and 302 engines prior to December 1982 were 28-ounce offset balanced, which means you need a 28-ounce offset balance flywheel or flexplate before you go to dynamic balancing. Since December 1982, 5.0L engines have a 50-ounce offset balance flywheel or flexplate. Harmonic balancers must have the corresponding 28- or 50-ounce offset balance.

There are three basic flywheel/flexplate sizes for the small-block Ford: 141/148-, 157-, 160-, and 164-tooth. The 148-tooth flywheel was conceived for the 1975–1978 Mustang II with 302-ci V-8. The 141-tooth flexplate was also con-ceived for the 1975–1978 Mustang II with the C4 Select-Shift. The 157-tooth flywheel/flexplate is the most common size; it is found in vintage Mustangs, Falcons, Fairlanes, and the like. The 164-tooth is for high-performance and heavy-duty applications such as full-size passen-ger cars and trucks.


This is a C9OE 351W connecting rod forging, 5.596 inches center-to-center, which was the same basic rod forging throughout the 351W’s production life. Expect to find a variety of forging numbers; however, the basic forging never changed. Treat this rod to a reconditioning and shot peening along with ARP 3/8-inch bolts for strength on the street and weekend racing. 


The three-bolt harmonic dampener (left) was used prior to 1970. Beginning in 1970, Ford went to a four-bolt dampener (right) on all V-8 engines. Small-block balancers vary in width  and markings depending on the  engine they’re intended for. Beginning  in December 1982, the 28-ounce offset balance was changed to 50 ounces to accommodate greater reciprocating weight in the 5.0L High Output engine. 



 Here are a 302 rod (left, C8OE) and a 351W rod (right, C9OE). The 302 is 5.090 inches center-to-center; the 351W is 5.596 inches center-to-center. The 221/260/289 rod (not pictured) is longer than the 302 rod at 5.155 inches center-to-center. 


This is a typical 1-inch-wide 221/260/289 harmonic dampener with a two-rung pulley prior to 1968. The dampener width directly affects pulley width and belt alignment.  The exception to this rule is when the pulley mounting face is positioned on a wider dampener. 


During a tear-down, be sure to check harmonic dampener condition and indexing. A harmonic dampener consists of a hub, rubber insulator, and an outer ring, which makes it a “dampener,” not a balancer. The harmonic dampener “dampens” combustion pulses around a crankshaft’s centerline. It acts as a shock absorber, limiting crank twist and rebound. 


Each flywheel/flexplate size calls for a matching bellhousing without exception. A 157-tooth flywheel/flexplate in a 164-tooth bellhousing means the starter won’t engage. A 157-tooth bell does not fit over a 164-tooth flywheel/flexplate. Bell and flywheel must match size-wise.

An even more confusing matter is the odd-duck flywheels and flex-plates you don’t hear about very often. Early small-block production from 1962 to 1966 consisted of the 160-tooth flywheel/flexplate, which was replaced by the 157-tooth conceived to improve starter engagement.

You can replace the 160-tooth flywheel/flexplate with a 157-tooth without consequence. It can get tricky with torque converter size and bolt pattern, which have been known to create conflict. Not all 160-tooth flex-plates interchange with a 157-tooth due to variations in torque converter bolt patterns. Also available was the heavy-duty 168-tooth flywheel/flex-plate, which was replaced by the 164-tooth for the same reason: to improve starter engagement.


This Tech Tip is From the Full Book, FORD SMALL BLOCK PARTS INTERCHANGE. For a comprehensive guide on this entire subject you can visit this link:


SHARE THIS ARTICLE: Please feel free to share this post on Facebook Groups or Forums/Blogs you read. You can use the social sharing buttons to the left, or copy and paste the website link:


Harmonic Balancers: 221/260/289/302/Boss 302

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. Pulley runout must be checked first. Ideally, you balance a large pulley right along with the harmonic balancer and flywheel/flexplate because all small-block Fords are externally balanced. However, if you ever need to change the pulley, you can run into balance issues there too.


This is the 113⁄16-inch 289 High Performance harmonic dampener. It is different than the nearly identical Boss 302 dampener because of its counter-weighting. The 289 High Performance engine has a stamped steel crankshaft counterweight behind the timing set. The Boss 302’s harmonic dampener has this counterweight incorporated into the dampener.


The standard 221/260/289 harmonic dampener is 1-inch wide. This is an aftermarket 221/260/289 dampener, which is clearly marked and easy to read. The factory dampener has smaller markings. 


On the left is a 1970 vintage 302 harmonic dampener with a 28-ounce offset balance. In 1968, small-block Ford dampeners became wider as a means of absorbing more harmonics in Ford’s quest for a smoother engine. On the right is a 5.0L dampener with a 50-ounce offset balance. 


This is a high-performance SFI-rated harmonic dampener from Ford Racing. When you order a dampener, keep engine’s offset balance in mind because these engines are externally balanced. Also consider dampener diameter and clearances, which can affect pulley alignment. 


Flexplates and flywheels are part of the external balancing common to small-block Fords. On the left is a 28-ounce offset balance flexplate for 221/260/289/302 prior to the 1982 model year. On the right is a 50-ounce offset balance flexplate for the late-model 1982–2001 5.0L High Output engines. Note the difference in balance weight sizing.


This is a 289 High Performance 157-tooth flywheel, which is unique to the Hi-Po engine because it is weighted differently than the 221/260/289 2V and 4V engines. Although it has a 28-ounce offset, it is counterweighted differently for the same reason it has a slide-on crankshaft counterweight. Note the orange paint mark indicating its 289 High Performance status.


The 221, 260, and 289 sharethe same basic harmonic balancer dimensionally with a 28-ounce off-set balance. However, the 289’s balancer is different from a part number standpoint. The 221 and 260 employ a C4OE-6316-A balancer instead of 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 larger in width at 337⁄64 inches wide. It is wider and heavier to compensate for the high revs and larger/heavier 3/8-inch rod bolts. The 1969–1970 Boss 302 balancer is also wider and on par with the 289 High Performance balancer.




The 351 Windsor’s nodular iron crankshaft has a 3.500-inch stroke and 3.000-inch main journals with a “3M” in the forwardmost counter-weight/journal. A forged steel crank-shaft was never available from the factory for the 351W. The 351W’s “3M” cranks are extremely durable and can take a lot of punishment given ample oil supply and commonsense engine tuning. When the 351W engine was upgraded to a onepiece rear main seal in 1985, its revised nodular iron crankshaft received a revised “7M” identification code. Later in production, it was identified as “7MA.”


Connecting Rods: 351W

The 351W connecting rod is 5.956 inches center-to-center regard-less of block deck height. Through-out the 351W’s long production life spanning 1969–1996, it employed the same basic connecting rod forging with 3/8-inch bolts. You can recondition and shot peen this rod, then fit it with 3/8-inch ARP bolts and wind up with a rod good for up to 500 hp. What’s more, you can do it with the stock “3M” or “7M” nodular iron crankshaft.


Three flywheel/flexplate sizes are available for small-block Fords: 157-, 164-, and 148-tooth. The 157-tooth is most common for vintage Ford applications. The 164-tooth is for high-performance/heavy-duty applications and is also used for the late-model 5.0L High Output with 5-speed. The petite 148-tooth is for the 1974–1978 Mustang II only. Each has its own bellhousing. 


The aftermarket offers a wealth of stroker kits for small-block Fords, including the 351C, 400, and 351M. If you choose to go with a stroker kit, keep block clearances in mind along with modifications that must be made to the block to clear rod bolts and crankshaft counter-weights. A good budget stroker kit includes a modular iron (cast steel) crankshaft, rugged I-beam rods, and forged pistons. You can build torque into your small-block with an economic stroker kit and complete the engine for less than $5,000.


Beginning in December 1982, Ford went to a one-piece rear main seal on the 5.0L engine, which is a better sealing system than the two-piece. The one-piece seal is a large-diameter seal with a garter spring reinforced lip. When installed properly, the one-piece seal is virtually leak-free for the life of the engine.


Chapter 2 discussed how to convert a two-piece main seal block to a one-piece. Any qualified machine shop can perform a one-piece seal conversion with a boring bar and a lathe. One-piece seal conversion should be a part of every engine build because it is very effective and not visible.


The 351C, including the Boss 351 and High Output, was never fitted with a forged-steel crankshaft. All were fitted with the “4M” nodular iron crankshaft with 3.500-inch stroke, 2.750-inch main, and 2.320-inch rod journals.



Although other Ford V-8 engine families had both cast and steel crankshafts, the 335-series engines were produced in cast only. Ford never produced a mass-production steel crankshaft for the 351C, 400, or 351M aside from perhaps racing and rare factory experimental “XE” pieces. Hank the Crank began producing steel Cleveland cranks in 1974 for drag racers. The aftermarket has followed suit with a great selection of cast, steel, and steel billet Cleveland cranks.

The 335-series factory nodular iron crankshaft is fully capable for use in high-performance applications up to 7,500 rpm and hasn’t exhibited extensive failure issues. Thousands of 351C engines have been raced over the past 40 years with cast cranks without consequence. The same can be said for the Cleveland’s connecting rods, which are very durable pieces with beefy large ends and 3/8-inch rod bolts.



From left to right are three 335-series Cleveland engine crankshafts: 351M with a 3.000-inch main and 3.500-inch stroke, 351C with a 2.750-inch main and 3.500-inch stroke, and 400 with a 3.000-inch main and 4.000-inch stroke. The 351M is identified with a “1K” casting mark. The 351C has “4M.” The 400 has “5M.” (Photo Courtesy Tim Meyer)


Here’s a typical 335-series connecting rod forging marked D0AE-A with 3/8-inch bolts. These are extraordinarily strong rods for a healthy street engine. All these rods require is shot peening, reconditioning, and ARP bolts. 


The 351C, 351M, and 400 have the same basic harmonic dampener, which is wider and four-bolt-only with the timing pointer on the passenger’s side of the engine. 


A closer look at the 351C connecting rod reveals broached-head 3/8-inch bolts and plenty of steel as a support system. 



Three factory nodular iron crank-shafts are identifiable by markings, stroke, and main journal dimensions. The 351C crank is marked with an identification of “4M” or “4MA.” You must be attentive regarding main journal size because it’s easy to unknowingly pick up a 351M crank, which has the 400’s larger 3.000-inch main journals along with the 351C’s 3.000-inch stroke and rod journals. The 351C has smaller 2.750-inch  main journals, which means you need the journals to be turned down by a competent machinist.

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


Pistons: 221/260/289/302

The aftermarket offers cast, hypereutectic, and forged pistons in all shapes and sizes for small-block Fords. The type of piston you use depends on your engine’s use. Cast and hypereutectic pistons are best for street use. Even a mild street 289 High Performance V-8 can get by with cast or hypereutectic pis-tons. Flat-top pistons in a Hi-Po net you 10.0:1 compression, depending upon compression height. Thing is, 10.0:1 can be risky depending on cam profile. For safety with compression around 9.0:1, 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 also increase compression.

Cast and hypereutectic pistons have a more conservative expansion rate, which makes them ideal for street use. They run quieter because they have tighter tolerances. Forged pistons are appropriate for racing and especially with nitrous, supercharging, or turbo-charging. Forged pistons, however, have a much greater rate of expansion, which calls for more generous tolerances. This means piston noise (rattle) during cold start and the need for careful treatment when cold. The rule is to use press-fit piston pins on cast and hypereutectic pistons and floating pins on forged pistons. But it’s a matter of personal preference.


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


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


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


Ford had 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 dished pistons to control and reduce compression. Compression depended upon the amount of dish volume. In 1968, combustion chambers became larger and more shovel shaped, which helped reduce compression and the corresponding emissions levels.


Piston Rings

Choosing the right piston ring for the job is actually more important than selecting the right piston. Conventional wisdom has long been 5/64-, 5/64-, and 3/16-inch ring packages. But that was back in the day when you could tolerate frictional losses and ring technology was less advanced.

Then, castiron rings were popular. Today, we have better ring materials such as premium-grade cast iron, ductile iron, and steel. Plasmamoly, chromemoly, and black-nitride coatings have made compression rings more durable. Nitrided steel seems to be the most popular for high-revving engines and high operating temperatures. Chromemoly is popular more for industrial applications.



To choose the correct piston ring package, it is important to understand how piston rings work. They contain compression and combustion gases, carry oil up the cylinder wall, and transfer heat from the piston to the cylinder wall and water jacket.

The top compression ring has the toughest job. It faces the extreme heat of combustion and seals the combustion chamber. You want the top compression ring to wear into the cylinder wall to form a perfect seal. This happens thanks to the bevel, or offset, around the inside circumference of the ring. Hot gases press against the bevel, or offset, forcing the ring against the cylinder wall to form a gas-tight seal.

The second compression ring, also known as an oil control ring, both seals the combustion chamber and carries oil up the cylinder wall. The second compression ring is a backup ring for the top compression ring and helps wipe excess oil from the wall.



The bottom oil rings carry oil down the cylinder wall and back to the sump. The expander between the two oil rings helps rings maintain tension throughout the life of the rings.

If you’re building a mild street engine, a good ductile iron ring is your best choice. If you’re going to run the engine hard, you want a steel ring with plasma-moly or black nitride, which perform well under demanding conditions. Chrome-moly is very hard, but it does not have the oil-carrying qualities of molybdenum. And because chrome-moly is hard, it can cause excessive cylinder wall wear. 


Written by George Reid and Posted with Permission of CarTechBooks


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