When the engine
was first overhauled, i.e. post-Barry scrapyard, it was known
that the cam unit was a loose fit onto the axle and, in order
to allow the overhaul to proceed without further delay and expense,
a shim was wrapped around the axle to allow the cams to be correctly
clamped down. This apparent "bodge" (see note 2 below) was known about and has lasted for 15 years of
quite heavy service. Unfortunately the shim had literally been
pounded into pieces so that the eccentrics were being driven
solely by the key which resulted in the knocking that was heard.
Using the key to drive put undue wear onto the keyway in the
bore which consequently increased its width, whereas the axle
keyway suffered less. Thus the new key had to be stepped to accommodate
the two widths. The shimming process will have to be repeated
to bring the engine back into service and the eccentric unit
is, effectively, scrap and will ultimately have to be replaced.