King CR4668SM0.25 Connecting Rod Bearing Set 0.25mm Undersize Hyundai Kia 2.4L G4KC G4KE

The King CR4668SM0.25 is a connecting rod bearing set engineered specifically for the Hyundai/Kia 2.4L G4KC and G4KE (Theta/Theta II) four-cylinder engine. CR4668SM0.25 is the 0.25mm undersize (0.010") variant, designed for engines whose crankshaft connecting rod journals have been reground to the first standard undersize during an engine rebuild. This set fits a wide range of vehicles including the Hyundai Sonata, Hyundai Santa Fe, Hyundai Tucson, Kia Optima, Kia Sorento, and Kia Sportage from 2006 through 2022. If your machinist has taken 0.25mm off the rod journals, CR4668SM0.25 is the correct bearing size to restore proper oil clearance and protect your rebuild.

King SM-Series Technology and Construction

The SM-Series designation stands for Strengthened Manganese aluminum alloy, King's strongest aluminum-based bimetal material for high-load and performance street applications. Every CR4668SM0.25 half-shell is built to exacting tolerances using a precision three-layer bimetal construction process.

• Steel backing: High-strength steel substrate provides dimensional stability and resists deformation under peak connecting rod loads.
• Aluminum bonding layer: Intermediate bonding layer ensures metallurgical adhesion between the steel backing and the bearing alloy for long-term durability.
• Strengthened Aluminum alloy face: The bearing surface uses an aluminum alloy strengthened with manganese and chromium additions, delivering higher fatigue strength than standard aluminum bearings while retaining excellent conformability and embeddability.
• Precision eccentricity: King machines a controlled eccentric profile into the bearing bore, promoting hydrodynamic oil film formation at startup and under load.
• Tight tolerance manufacturing: Each shell is manufactured in Kiryat Gat, Israel, on precision grinding equipment to meet or exceed OEM clearance specifications for the G4KC/G4KE engine family.
• High-load street application: The SM-Series is rated for high-load street and performance use, making it appropriate for rebuilt daily drivers, sport compacts, and moderately tuned Hyundai/Kia 2.4L engines.
• Locating lug included: CR4668SM0.25 features a locating lug that indexes the shell into the connecting rod bore, preventing rotation during installation and operation.

Understanding Bearing Undersizes: When to Use CR4668SM0.25

Connecting rod bearings are sized to match the diameter of the crankshaft's rod journals. Over time, journal surfaces develop wear, scoring, or out-of-round condition. During an engine rebuild, a machinist will measure the journals and, if needed, grind them to a smaller, perfectly round diameter. A new, thicker bearing is then installed to restore the correct oil clearance.

The 0.25mm undersize designation on CR4668SM0.25 means the bearing is sized for crankshaft rod journals that have been ground 0.25mm (approximately 0.010") smaller than the original factory specification. This is the first standard undergrind, often called "10 over" in traditional rebuilding terminology, and it is the most commonly needed undersize when journals show minor wear.

How to determine which size you need:

• Have your machinist measure each rod journal with a micrometer. Compare the reading to the factory specification for the G4KC or G4KE engine.
• If journals are within 0.001" of standard, use CR4668SM (STD).
• If journals have been ground to -0.010" (0.25mm under factory spec), use CR4668SM0.25 (this part).
• If journals have been ground to -0.020" (0.50mm under), use CR4668SM0.5.
• If journals have been ground to -0.030" (0.75mm under), use CR4668SM0.75.
• Never mix undersize bearings. Install the same undersize on all four connecting rods.
• Always verify the final bearing clearance with Plastigage after installation before assembling the engine.

CR4668 Size Family: SM-Series and XP Race-Grade Comparison

King offers the CR4668 connecting rod bearing for the Hyundai/Kia 2.4L G4KC/G4KE engine in multiple sizes and material grades. The SM-Series covers standard and undersize street/performance applications. The XP-Series steps up to tri-metal construction with pMax Black DLC coating for race and high-boost use.

What's Included

The CR4668SM0.25 ships as a complete connecting rod bearing set for one four-cylinder engine. The set contains:

• 8 individual half-shells (4 pairs, also described as 4 upper shells and 4 lower shells)
• Each connecting rod journal requires one upper half-shell and one lower half-shell, totaling 2 shells per cylinder
• 4 cylinders x 2 shells = 8 pieces total for a complete connecting rod bearing replacement on the Hyundai/Kia 2.4L G4KC/G4KE four-cylinder engine
• All shells include the factory-style locating lug for correct indexing in the connecting rod bore
• No additional hardware or separate shell purchases required for a complete rod bearing replacement

Note: This set covers connecting rod bearings only. If you are performing a complete engine rebuild, you will also need a separate main bearing set for the G4KC/G4KE crankshaft main journals.

Vehicle Fitment

CR4668SM0.25 fits the Hyundai/Kia 2.4L G4KC and G4KE (Theta/Theta II) inline four-cylinder engine. Confirm your engine code before ordering. This bearing set is for the 2.4L G4KC/G4KE only and does not fit the 2.0L G4KA, the 2.4L G4KJ, or any turbocharged 2.0T variants.

Full Specifications

Warranty and California Prop 65 Notice

King Engine Bearings supports all manufacturer warranty claims through their i-King online registration portal. Register your CR4668SM0.25 set at kingbearings.com after installation to track your warranty information. Warranty claims are available to the original purchaser only. Specific warranty duration should be confirmed directly with King Bearings or an authorized US distributor at time of purchase.

Magnuson-Moss Warranty Act: Installing aftermarket engine bearings during an engine rebuild does not automatically void your vehicle's remaining factory warranty. Under the federal Magnuson-Moss Warranty Act, a dealer or manufacturer cannot void your powertrain warranty simply because you used an aftermarket bearing unless they can demonstrate that the aftermarket part directly caused the failure being claimed.

California Proposition 65 Warning: This product can expose you to Nickel, which is known to the State of California to cause cancer, birth defects, or other reproductive harm. For more information, go to www.p65warnings.ca.gov.

About King Engine Bearings

King Engine Bearings Manufacturing and Marketing Ltd. is headquartered in Kiryat Gat, Israel, where all King bearings are engineered and manufactured. Founded on precision bearing technology developed for motorsport applications, King has grown into one of the most trusted names in OEM-replacement and performance engine bearings worldwide. Their product line covers thousands of passenger car and light truck applications, with dedicated race-grade XP-Series bearings for high-boost and high-RPM competition engines.

King's manufacturing process emphasizes tight dimensional tolerances, controlled eccentricity profiles, and rigorous material selection. The SM-Series, represented by CR4668SM0.25, is King's premium aluminum-based bimetal product, designed for demanding street and performance applications where a standard aluminum bearing would not provide adequate fatigue resistance. King bearings are distributed globally through authorized channels including major US retailers such as AutoZone and RockAuto.

Frequently Asked Questions

What does the 0.25mm undersize mean on the CR4668SM0.25?
It means the bearing is designed for a crankshaft whose connecting rod journals have been precision-ground 0.25mm (0.010") smaller than the original factory diameter. This is the first standard undergrind in engine rebuilding. If your crankshaft has not been ground and is still at factory specification, you need the standard-size CR4668SM instead.

How do I know if I need the 0.25mm, 0.50mm, or 0.75mm undersize?
Your engine machinist will measure each connecting rod journal with a micrometer and compare it to the factory specification for the G4KC or G4KE engine. The difference between the measured diameter and the factory spec tells you which undersize bearing to order. Never guess the undersize: installing the wrong size bearing will result in incorrect oil clearance, premature bearing failure, or immediate engine damage.

Will the CR4668SM0.25 work if my crank has not been reground?
No. The CR4668SM0.25 is thicker than a standard bearing to compensate for the smaller journal diameter after grinding. Installing a 0.25mm undersize bearing on a standard, unground crankshaft will result in zero oil clearance and immediate bearing seizure. Use the standard CR4668SM for an unground crank.

What engine codes does this bearing fit?
CR4668SM0.25 is engineered for the Hyundai/Kia 2.4L G4KC and G4KE (Theta and Theta II) inline four-cylinder engines. These engines appear in the Hyundai Sonata, Santa Fe, and Tucson, as well as the Kia Optima, Sorento, Sportage, Forte, and Rondo across various model years. It does not fit the 2.0L G4KA, the 2.4L G4KJ, or any turbocharged engine variant. Always confirm your engine code before ordering.

How do I install connecting rod bearings correctly?
Connecting rod bearings require a complete engine teardown to the short block. Clean the rod bore and cap thoroughly, check for scoring or damage in the bore, and apply a light coat of clean engine assembly lubricant or oil to the bearing face before installation. Install the shell with the locating lug aligned to the notch in the rod bore. Torque the rod cap to the G4KC/G4KE factory specification. Always check final oil clearance with Plastigage before final assembly. This is a job for someone with engine rebuild experience or a qualified machine shop.

Is the CR4668SM0.25 the same as the CR4668XP0.25?
No. Both fit the same application at 0.25mm undersize, but they use different materials and are suited to different use cases. The CR4668SM0.25 (this part) is a bimetal bearing with a strengthened aluminum alloy face, ideal for street rebuilds, daily drivers, and lightly modified engines. The CR4668XP0.25 is a tri-metal race-grade bearing with a steel backing, bronze intermediate layer, and pMax Black DLC coating, designed for high-boost, high-RPM competition engines. For a stock or mildly tuned street rebuild, the SM-Series is the appropriate choice and is more cost-effective.

Does this product carry a Prop 65 warning?
Yes. The CR4668SM0.25 carries a California Proposition 65 warning for Nickel, which is known to the State of California to cause cancer, birth defects, or other reproductive harm. This warning applies to the metallic alloy construction of the bearing. For more information, visit www.p65warnings.ca.gov.

How many bearings come in the set? Do I need to buy more than one set?
One set of CR4668SM0.25 contains 8 half-shells (4 pairs), which is exactly the correct quantity for a complete connecting rod bearing replacement on a four-cylinder G4KC/G4KE engine. You do not need to purchase multiple sets. One set replaces all four connecting rod bearings in the engine.

Will installing these bearings void my Hyundai or Kia warranty?
Under the federal Magnuson-Moss Warranty Act, a manufacturer or dealer cannot void your factory powertrain warranty simply because you installed an aftermarket part. They would need to demonstrate that the aftermarket bearing directly caused the specific failure being claimed. If your vehicle is still under an active factory warranty, consult with your dealer before performing engine work.

Where are King Engine Bearings manufactured?
All King Engine Bearings products, including the CR4668SM0.25, are manufactured in Kiryat Gat, Israel, at King Engine Bearings' own production facility. King bearings are not manufactured in China or through a third-party contract manufacturer.