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Re-building a high-horsepower Cummins N14, Cat C15, or Detroit Series 60 engine with pitted, worn, or uneven liner counterbore ledges? Installing fresh wet cylinder liners onto damaged counterbores is an absolute financial trap. The M50133 / PT2250-B Upper Deck Counterbore Tool machines counterbore ledges down to absolute flat concentricity, restoring exact factory liner protrusion and stopping head gasket blowouts before they start.

The Critical Physics of Cylinder Liner Protrusion and Ledge Fretting

On heavy-duty wet-sleeve diesel platforms like the Cummins 855/N14, Caterpillar 3406E/C15, Detroit Diesel Series 60, and Navistar DT466, the upper cylinder deck ledge supports the entire clamping force of the liner flange. Under continuous high-load thermal expansion and firing pressure, the metal-on-metal interface between the liner flange and the block counterbore suffers from micro-movement—a condition known as counterbore fretting. Over time, fretting carves deep ridges, rust pits, and uneven low spots into the cast-iron ledge. When a technician drops a new cylinder sleeve into an un-machined, fretted counterbore, the sleeve sits unevenly or below the block deck face. This incorrect liner protrusion leaves the cylinder head gasket fire-ring with insufficient clamping pressure. Within miles of highway operation, peak combustion pressures blow past the fire-ring, scouring the deck, contaminating the cooling system, and dropping cylinder compression. The M50133 upper deck counterbore cutter solves this structural defect completely. Featuring a self-centering base housing that accepts application-specific cutter plates, it allows machinists and engine builders to resurface counterbore ledges back to absolute parallel levelness right on the block—setting a perfect foundation for correction shims and fresh liner flanges.

• Universal Multi-Engine Versatility – Modular base housing accepts interchangeable cutter plates to machine upper deck ledges on Cummins 855/N14/NH, Cat 3406/C15, Detroit Series 60, and Navistar DT466 blocks.
• Direct OEM Factory Tool Interchange – Direct high-strength replacement for legacy Kent-Moore / Porta-Tool models **PT-2250-B**, **PT2250**, and **PT2200**.
• Self-Centering Precision Drive – Automatically centers itself over the cylinder bore to ensure uniform, concentric depth cuts across every cylinder deck ledge.
• Standardized Replacement Carbide Bits – Utilizes standard industry **PT2200-93-6** cutter bits for clean, chatter-free machining passes in tough cast iron.
• Heavy-Duty Industrial Machining Mass – Weighing a solid 56.00 lbs, this industrial-grade steel fixture absorbs vibration to produce smooth, mirror-like counterbore surfaces.

Stop Gambling on Uneven Counterbores. Command Absolute Block Authority.

The M50133 / PT2250-B Upper Deck Counterbore Tool is an essential capital asset for commercial diesel machine shops, heavy equipment rebuild facilities, engine remanufacturers, and fleet overhaul bays. Protect your engine rebuilds, eliminate recurring head gasket failures, and machine with absolute mechanical precision with Apex.

Technical Specifications

Technical Metric	Value / Fitment Reference Guidelines
Engine Compatibility Profile	Cummins 855/N14/NH, CAT 3406/C15, Detroit Series 60, Navistar DT466
Primary Machining Function	Upper deck counterbore ledge machining, fretting repair, shim ledge correction
OEM / Porta-Tool Cross Reference	Kent-Moore Porta-Tool PT-2250-B, PT2250, PT2200
Replacement Cutter Bit Standard	PT2200-93-6 Carbide Cutting Bit
Plate Attachment System	Interchangeable application-specific cutter plates (sold separately)
Total Shipping Weight	56.00 lbs (Heavy-duty vibration-damping shop fixture)

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