The Rear Inlet Valve No.A2 Cylinder
from Rolls Royce Merlin XX.37673

This photograph was taken by Rolls Royce on 18 June 1942, Ref No.G628.

This image, is the broken rear inlet valve from Merlin type XX engine No.37673, it 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.

Rolls-Royce determined then that a single nut left un-tightened had caused the crash and recommended
that in future a senior Non Commissioned Officer should be responsible for checking that all
tappet locking nuts were tightened after the fitter had worked on them. The report also, sadly, highlighted the fact
that the loss of an aircraft due to a single tappet nut being left unscrewed was known to them,
but the contingency plans that were designed to alleviate this problem had not yet been put into
operation and Rolls-Royce had not seen fit to warn the fitters.

This photograph has NEVER been published before and has been missing for the last 61 years.

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