Had to do it a few times as a 1-11 pilot. Once down route in Tripoli and we were very keen to leave. I seem to remember it was a valve in the pneumatic starting system playing up. There was also one in the sub wing to the engine cowl, and we had a rod thing in the cockpit to give it a twist. As you were locking up the cowl it was a bit noisy!!
All part of the fun in those days.