37 repairing, maintaining, and servicing engines, tractors, motor graders, loaders, tractor-scrapers, off-highway trucks, fork lift trucks, straddle carriers, log skidders, pipe layers, electrical generating sets, compressed air equipment, cranes, excavators, and parts therefor, designing, laying out, and supervising and installation of shelving and storage facilities; repairing, maintaining, and servicing air-driven tools, backhoe loaders, articulated dump trucks, paving equipment, compactors, wheel dozers, mechanized tree harvesters, mechanized tree processors, and parts, attachments, and accessories therefor