On one of my early (constituted) crews, we had a Flight Engineer who always brought with him a long metal pole when we went on detachment/land-aways. He would never say what it was for until one day when one of the inboard engines would not start. HAving already been introduced to the 'kick start' procedure by another crew (rushing down the runway on 3 then unfeathering the recalcitrant engine at about 80kts!) I assumed that's what would come next. In fact, all the Eng did was climb out on the wing through the overwing hatch, open up the top panels and thread his long pole through the innards, before taking the big mallet from the tool kit and giving it an almighty wack - again felt throught the whole airframe. He then reassembled everything, pressed the start button and everything worked as advertised.
He subsequently showed me that it was the easiest way of getting the start solenoid to work as they had a propensity to stick, and he had been shown the trick (he said) on Lancasters.