Cummins ISX In-Frame Overhaul Kits: How to Choose the Right One

If you're rebuilding your Cummins ISX or X15 engine, selecting the correct in-frame kit is not just a detail—it's mission-critical. Mismatched liners, incorrect rod types, or missing shims can cost you thousands in labor, parts, and downtime. In this guide, we’ll walk you through exactly how to identify your liner configuration, understand Cummins’ evolving engine designs, and confidently select the right overhaul kit.

Understanding the Importance of Proper Kit Selection

Cummins ISX/QSX engines have gone through multiple revisions over the years, especially post-2010. These changes affect:

• Cylinder liner outside diameter (OD)

• Liner seat type and use of shims

• Connecting rod type (saw cut vs fractured split)

• Anti-polishing ring design

Because of this, you cannot rely solely on the engine model or CPL number. You must measure and inspect your engine block to determine:

1. The liner OD at the sealing area

2. The presence and number of grooves at the bottom of the liner

3. Whether the engine uses a shim under the liner

4. The type of connecting rod in use

Getting this wrong means the liners won’t seat, the rods won’t install correctly, or the engine will fail prematurely due to oil consumption, blow-by, or cracked components.

Step 1: Measure the Liner Outside Diameter (OD)

Cummins ISX/QSX engines use two primary liner diameters: 150mm (5.906 inches) and 152mm (5.984 inches). This measurement must be taken at the O-ring groove or sealing band area, not the mid-body or top flange.

In 2010, Cummins introduced a revised block casting that supported the larger 152mm liner to improve durability. However, some engines were rebuilt with aftermarket or service parts that complicate identification, so visual inspection is not enough.

Use a micrometer or a bore gauge to measure the outside of the liner where the liner meets the O-rings. If it’s:

• 150mm (5.9060 in) → You need a 150mm liner kit

• 152mm (5.9840 in) → You need a 152mm liner kit

Never mix liner sizes in the same block. All six liners must match in OD and design.

Step 2: Identify Anti-Polishing Ring and Shim Configuration

Cummins implemented an "anti-polishing ring" design to reduce oil consumption and carbon buildup at the top of the cylinder. These rings can be visually identified by the number of grooves machined around the liner:

If your liner has two grooves at the bottom, it originally came with a liner shim. This shim ensures correct liner protrusion height and sealing pressure.

• You must use a new shim if the original is removed.

• Liners with only one groove are no-shim designs and cannot accept shims.

Never reuse a shim from a previous install. Doing so compromises seal integrity and can lead to premature liner failure or head gasket issues.

Step 3: Determine Connecting Rod Type

ISX engines come with two types of connecting rods:

1. Saw Cut Rods

• Older design

• Machined flat surface where cap meets rod

• Typically found in engines built pre-2010

2. Fractured Split Rods

• Newer OEM standard

• Rod and cap are made as one piece, then fractured

• Has a jagged break surface for perfect alignment

• Cannot be swapped with saw-cut styles

Why it matters:

• Fractured rods use different torque specs and bolts

• Replacing fractured rods with saw-cut rods (or vice versa) will cause catastrophic imbalance

• The in-frame kit must include the correct bearing sets and bolts based on rod type

Always visually confirm your rod type before ordering.

Step 4: Use CPL Number for X15 Engines

If you have a Cummins X15, you can often reference the CPL (Control Parts List) number to select the right in-frame kit. Common CPL-to-kit matches include:

Even with CPL numbers, it's always best to confirm physical measurements when possible.

Matching the Right Kit to Your Engine

Here’s a sample breakdown of popular in-frame kits and their application criteria:

All of these must be selected based on physical confirmation. Don’t guess. Don’t assume. Measure and inspect.

Final Thoughts: Get It Right the First Time

When you're 1,000 miles from home and your engine is in pieces, the last thing you want is to realize you ordered the wrong in-frame kit. Avoid costly mistakes by:

• Measuring your liner OD with a micrometer

• Counting the anti-polishing grooves

• Checking for liner shims

• Identifying your rod type

If you're unsure, take clear photos of your liner and rods and call an expert.

Need help? Call Texas Truck Market at 832-867-3345. We specialize in ISX and X15 kits and can walk you through the process. Whether you’re wrenching in the driveway or running a fleet, we’ll make sure you get the right parts, the first time.

Order Your Cummins In-Frame Kit Today

We carry:

• ISX15 and X15 kits (150mm & 152mm)

• Fractured and saw-cut rod configurations

• Shim and no-shim liner styles

• Kits matched to CPL numbers

Backed by warranty, available for same-day shipping, and eligible for financing. Give us a call or shop online to get started.