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Rebuilding or re-lining a Detroit Diesel DD15 or DD16 engine suffering from counterbore fretting, erosion, or uneven liner protrusion? Attempting to install fresh cylinder liners over fretted or pitted upper counterbore ledges without precision machining leads directly to crushed liner flanges, uneven deck clamping, and blown head gaskets. Scraping an entire engine block over minor counterbore damage burns thousands of dollars in shop capital. Engineered for precision machine shops and commercial engine rebuild stalls, the M50166 Counterbore Shim Cutting Tool provides a rigid, plate-guided machining fixture and micro-adjustable carbide cutter bit to cut counterbore ledges dead-flat and true, enabling exact liner shim installation to restore factory protrusion specifications.

The Critical Physics of DD15/DD16 Counterbore Fretting & Liner Protrusion Stability

Heavy-duty Detroit Diesel DD15 and DD16 14.8L/15.6L engines operate under extreme cylinder firing pressures exceeding 2,700 PSI. The top flange of each wet cylinder liner rests directly upon a narrow counterbore ledge machined into the cast-iron cylinder block deck. Over hundreds of thousands of heavy haul miles, continuous combustion shock loads and microscopic liner movement cause severe fretting corrosion, pitting, and depth variations around the counterbore landing. When counterbore depth becomes uneven across a cylinder, installing a new liner without machining creates a disastrous mechanical condition. The uneven landing tilts the liner flange, causing high-point stress concentrations that crack the liner lip or allow high-pressure combustion gas to scour past the head gasket. Furthermore, uneven liner protrusion across adjacent cylinders ruins cylinder head clamping torque. The M50166 Counterbore Shim Cutting Tool completely solves this short-block machining challenge. Featuring a precision-ground cutter plate that bolts directly to adjacent head bolt holes on the DD15/DD16 block deck, the tool aligns its carbide cutting bit perfectly perpendicular to the cylinder bore axis. Turning the micro-adjustable feed shaft shaves away damaged, fretted metal in controlled thousandths-of-an-inch increments, producing a glass-smooth, perfectly flat counterbore landing. Technicians can then insert stainless steel counterbore shims to bring liner protrusion back to exact Detroit OEM factory tolerances, saving high-value engine blocks from the scrap heap.

• Dedicated Detroit DD15 & DD16 Application Coverage – Purpose-built specifically for machining upper deck liner counterbores on Detroit Diesel DD15 (14.8L) and DD16 (15.6L) engine blocks.
• Complete In-Frame Machining Assembly – Includes heavy-duty base cutter plate, precision feed arbor, and carbide cutting bit (compatible with replacement bit part **M50167-3**).
• Saves Damaged Engine Blocks – Restores fretted, pitted, or uneven counterbores back to true flat spec, allowing precise liner shim installation instead of block replacement.
• Guarantees OEM Liner Protrusion & Deck Sealing – Eliminates uneven flange clamping and liner lip cracking to ensure leak-free head gasket sealing.
• Industrial Heavy-Duty Machine Shop Tooling – Substantial 58.00 lbs solid alloy steel construction built for daily continuous service in commercial engine remanufacturing plants and repair stalls.

Stop Scrapping DD15 Blocks. Command Total Detroit Counterbore Machining Precision.

The M50166 Counterbore Shim Cutting Tool – Detroit Diesel DD15 / DD16 is an essential capital asset for commercial truck overhaul centers, Detroit Diesel dealership service bays, engine remanufacturers, and heavy diesel machine shops. Recover fretted engine blocks, guarantee exact liner protrusion, and machine DD15/DD16 counterbores with complete mechanical authority using Apex tools.

Technical Specifications

Technical Metric	Value / Fitment Reference Guidelines
Target Engine Platforms	Detroit Diesel DD15 (14.8L) and DD16 (15.6L) Heavy-Duty Engines
Primary Operational Function	Precision machining and resurfacing of upper deck cylinder liner counterbores
Included Hardware Components	Main cutter plate, drive arbor assembly, feed mechanism, & carbide cutting bit
Replacement Cutter Bit Part Number	M50167-3 (Replacement Carbide Cutter Bit)
Part / Model Reference Number	M50166 (M50166 / 50166)
Total Package Shipping Weight	58.00 lbs (Substantial, professional machine shop grade service tool)

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