hammer blow

hammer blow (plural hammer blows)

1. A blow with a hammer.
2. (rail transport) A pounding of the rails by the driving wheels of a steam locomotive caused by the inertia of unbalanced parts.
   • 1959 September, P. Ransome-Wallis, “The British Railways Class "9" 2-10-0s”, in Trains Illustrated, page 419:

     The balancing of the engine is unusual, with the rotating masses fully balanced and 40 per cent of the reciprocating masses statically balanced by lead weights in the coupled wheels; the reciprocrating balance weights are in the same phase on both sides of the engine. This system saves balance weight and reduces the wheel hammer-blow.

• hammerblow

• “hammer blow”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.
• “hammerblow”, in Merriam-Webster Online Dictionary, Springfield, Mass.: Merriam-Webster, 1996–present.