The ATC-8321 / PT-8321 Lower Repair Ring Finished Bore Bushing (+.30 OD) is a precision-engineered oversized repair insert designed specifically for heavy-duty Caterpillar 3400, 3406, and 3408 diesel engine blocks. This finish-machined bushing restores a worn or damaged lower repair ring bore by providing a uniform, hardened surface that accepts repair rings with factory-level sealing integrity. Unlike standard size inserts, the +.30 OD oversize version is intended for conditions where the original bore has experienced greater wear or damage and requires a larger calibrated insert to bring the bore back to correct dimensions.
In high-hour engines such as Cat 3406 and 3408 powerplants, bore wear, corrosion, or over-machining can compromise lower ring support surfaces, resulting in reduced sealing performance, uneven ring seating, and accelerated wear. Installing an oversized, finished bore bushing like the ATC-8321/ PT-8321 allows rebuilders to salvage the block, avoid costly casting replacement, and restore dimensional control, concentricity, and long service life without additional machining.
This oversized bushing is ideal for engine rebuild shops, remanufacturing facilities, and fleet maintenance operations that demand precision and durability in heavy-duty engine repairs. Because the bore is finished at the factory, it typically requires no further honing or machining after installation, accelerating turnaround time on overhauls.
Key Features & Benefits
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Oversized +.30 OD design for addressing significant lower ring bore wear beyond standard insert correction.
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Precision finished bore — ready for immediate use without additional machining.
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Engineered for Caterpillar 3400, 3406, and 3408 engine groups.
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Restores bore concentricity and improves lower repair ring sealing integrity.
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Saves time and cost compared to full block replacement or extensive re-machining.
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Durable insert suitable for professional rebuilders and diesel machine shops.
Applications
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Lower repair ring bore restoration on Cat 3400, 3406, and 3408 engine blocks
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Heavy-duty diesel engine rebuilds and overhauls
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Block reconditioning in fleet maintenance, remanufacturing, and professional diesel shops
