The Rocker Arm with Tappet
This photograph is believed to have been taken by Rolls Royce between 18-23 June 1942.
This image, believed to be one of the rocker arms from Merlin type XX engine
No.37673, was eventually
concluded to have been the part-cause of the crash of Halifax V9977 on 7 June 1942.
It seems that during the last 30-hour inspection carried out at Defford between
25 May, and 1 June 1942,
a fitter had not sufficiently tightened one of the locking nuts that held the rear inlet valve in place.
With this locking nut loose, the vibration of the aircraft in flight eventually caused it
to unscrew allowing the inlet valve to travel far more than normal. Under enormous pressure,
the stem of the valve finally broke causing the charge of incoming fuel to have free access
to the outside of the rocker cover of the engine. As the fuel was pumped into the valve space
and ignited by the spark plugs it would be able to freely spread past the engine cover
and out into the space around the engine itself. All of this would have happened in a matter of seconds
after the initial failure of the inlet valve stem.
This photograph has NEVER been published before and has been missing for the last 61 years.