To better understand steel terminology, as is used by SAE and AISI, we can dissect the steel grade to determine some basic information. For example, the number 4340 can be broken down into two sets of digits. The number 43 represents the primary composition of the crankshaft beyond iron, which in this case includes nickel, chromium and molybdenum. The second set of digits represents the amount of carbon present in the steel in hundredths. Therefore, the number 40 represents a .40% carbon content.

4340 Crankshafts

4340 steel crankshafts contain 1.82% nickel, .50-.80% chromium, .25% molybdenum and .40% carbon. The remaining composition is primarily made up of iron (95-96%). This is one of the most common steels used for both aftermarket crankshafts and connecting rods. 4340 steel has a tensile strength that equals or exceeds 108,000 PSI. Because of the composition of this material, it responds well to heat treating and the final piece is quite durable.

4330 Crankshafts

Similar to the 4340 classification, 4330 steel crankshafts primarily consist of 95-98% iron, 1.82% nickel, .50-.80% chromium and .25% molybdenum. However, 4340 steel does have a lower carbon content of .30%. 4330 crankshafts have a high tensile strength that exceeds 125,000 PSI. Although a high tensile strength is desired in high performance applications, 4330 steel is less resilient to fatigue and is more prone to break if the crankshaft flexes.

4130 Crankshafts

4130 steel crankshafts contain .50-.95% chromium, .12-.30% molybdenum, .40-.60% manganese, .28-.33% carbon and an iron content that ranges from 97-98%. With a 66,700 PSI tensile strength, this is one of the weakest alloy steels used in aftermarket crankshafts. However, 4130 is ideal for light performance applications and often appeals to consumers because the cost is considerably less than higher grade steels.

5140 Crankshafts

Although less popular, 5140 steel crankshafts are used in mild performance applications and are classified in the chromium steel category. These crankshafts are comprised of 97-98% iron, .70-.90% manganese, .70-.90% chromium and .38-.43% carbon. 5140 steel crankshafts also contain lesser amounts of silicon, sulfur and phosphorous. 5140 steel has a tensile strength of 82,700 PSI, making it less brittle when compared to 4330 or 4340 steel crankshafts.

So which type of steel is best for your crankshaft? This determination is based on ones horsepower requirements and budget. Generally speaking, we prefer 4340 steel over all other options, particularly if the existing crankshaft can’t be repaired. There are many 4340 steel crankshafts powering engines that exceed 1,000 HP, which have proven to be quite durable for racing applications. Although many automotive enthusiasts like to compare 4330 –vs- 4340 steel, for example, their material compositions are not that dissimilar. How the crankshaft is hardened is more detrimental in obtaining the benefits from the composition of each crankshaft.

Now that you have learned more about the most popular grades of steel that are used to manufacture crankshafts, please rate this page below.

Those who own performance engines, and want to gain the most horsepower possible, often seek the services of an automotive machine shop that provides a crankshaft knife edging service. Normally reserved for racing applications, a knife edged crankshaft can help the engine produce more horsepower. Below we will look at how the knife edging process is completed and the benefits it offers.

As you can tell by the picture to your left, a knife edged crankshaft refers to the shape of the crankshaft’s counterweights. Removing this material and bringing it to a sharp edge does a couple of things. First, knife edging can often remove pounds of weight from a V8 crankshaft. Even some V6 crankshafts will realize a significant weight reduction when the counterweights have been knife edged. Less weight equates to a rotating assembly that spins with less resistance, and this in itself is responsible for some gains in horsepower. Knife edging also reduces friction, which is explained below.

The counterweights on most crankshafts are flat on the ends. As the crankshaft rotates, these counterweights come into direct contact with the engine’s oil. This contact creates friction and splashes oil all over the bottom end of the engine. A knifed edged crankshaft actually glides through the oil much easier and encounters far less friction. Anytime friction can be reduced in an engine’s rotating assembly or valvetrain, additional horsepower gains are realized.

There are many automotive machine shops that provide crankshaft knife edging services. However, how these shops perform the machining process does vary. Most machine shops will use a Bridgeport milling machine to rough in the counterweights, whereas some shops will simply grind the counterweights to a point. Regardless of which technique is used to perform the knife edge service, there are some steps that the machinist must take to protect the crankshaft prior to the machining operation.

Ideally, it is best to knife edge a crankshaft before any finish machining operations are performed. For example, if the crank needs to be ground or polished, these processes should be performed after the knife edging tasks are completed. The reason for this is that there is the potential for a grinding stone or tool to slip and come into contact with a journal. Although rare, particularly among experienced machinists who have knife edged many crankshafts, it is best to err on the side of caution.

Because of the material being removed from the crankshaft’s counterweights during a knife edging process, the rotating assembly will need to be balanced when the crankshaft is finished. Often lighter rods or pistons can help compensate for the crankshaft’s reduced weight. By properly planning for the reduced weight of a knife edged crankshaft, these variables can be considered first so that the need for heavy metal during balancing is greatly reduced.

Now that you have learned more about how the knife edging process can help to reduce a crankshaft’s weight and friction, please consider rating this page below so that we can further improve upon the information that we present to our valued visitors.