Integrated drilling rigs on modified chassis fall under Heading 84.30, not special purpose motor vehicles under Heading 87.05.

Water well drilling rigs mounted on motor vehicle chassis were held classifiable under Heading 84.30 where the evidence showed permanent and substantial integration of the modified chassis with the drilling machinery. Extensive fabrication, welding, strengthening, and replacement of parts meant the chassis lost its original transport function and became an inseparable part of an integral mechanical unit specially designed with the rig. The earlier Supreme Court decision was distinguished on facts because it lacked proof of such integration. On that basis, the goods were not treated as special purpose motor vehicles under Heading 87.05, and the consequential duty demand failed.

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Issues: Whether water well drilling rigs mounted on motor vehicle chassis were classifiable under Heading 84.30 as self-propelled wheeled machines forming an integral mechanical unit, or under Heading 87.05 as special purpose motor vehicles, and whether the resulting classification entitled the assessees to the consequential duty relief.

Analysis: The classification dispute turned on whether the chassis and drilling rig were merely mounted together or whether the chassis underwent permanent and substantial modification so that both elements were specially designed for each other and formed a single integrated unit. The earlier Supreme Court ruling on drilling rigs mounted on chassis was distinguished on facts because that case proceeded on the absence of evidence showing such integration. Here, the record showed extensive fabrication, welding, strengthening, replacement of parts, and permanent alteration of the chassis so that it could no longer serve its original transport function and became an inseparable part of the drilling rig. On that factual basis, the goods answered the description of self-propelled wheeled machinery under Heading 84.30 rather than special purpose motor vehicles under Heading 87.05.

Conclusion: Classification under Heading 84.30 was upheld, the demand for differential duty failed, and the Revenue's appeals were rejected.

Final Conclusion: The orders in appeal were sustained because the drilling rigs were found to be completely integrated with the modified chassis and therefore outside the Revenue's proposed classification.

Ratio Decidendi: Where the evidence shows permanent and substantial integration of a modified chassis with the working machine so that both are specially designed for each other and form an integral mechanical unit, the goods fall for classification under Heading 84.30 and not under Heading 87.05.

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