Possible Clues:

• Valved pipe — favourite part of 13 part 2, perhaps
• 'Knock it into the engine, by the sound of it (6)'
• That hospital avoided getting medical gear caught in part of machine
• Knock it, by the sound of it, in the engine
• Sliding rod in an engine
• Give the little dear a little knock in the engine
• Little blow to the little dear in the engine
• Sounds like what to do for a knock in the engine
• Click and Clack, the ___ Brothers
• Give it a knock in the engine, by the sound of it