be Dragons.

changed the inner engine oiling systems on nines many times, which
has lead to many an engine being built to fail. If you mix parts from
different years you can easily end up with loss of oil pressure and
failed bearings….even seen one with just the wrong front cam bushes
and that lead to disaster.

pit falls are the differences between internal and external rocker
feed engines.
were made with external feed via a small pipe from the blow off valve
or top of pump take off to the rockers through the top of the timing
chest. The head has drain back at the front and this runs down
through the block to holes in the cam bushes.
Riley changed to internal oil feed the drain back became the feed and
the casting covered more of the cam bush. Oil was passed from the top
of the inner pump take off via a larger pipe to a cross drilling that
feeds the idler gear spindle and both cam bushes. These bushes have a
grove around them and oil carries on up through the block and head
into the rocker boxes. These parts are all different to the earlier
and later external feed which was reintroduced in later 1934 and
carried on into the Merlin range.
the later external type oil feed to the same cross drilling, these
cam bushes have no grove, and a banjo bolt allow for oil to the
rocker externally. Oil drain back at the front of the head again.
have seen external pipes fitted on to internal rocker boxes that then
allowed oil out of the feed holes to atmosphere, and internal with
the wrong shaft so on oil can get into it at all….maybe should not
say Dragons…should
be Clowns.
is the design changes to the internal air bell, some years have a
long thin one that sockets into a small hole in a casting rib that is
not drilled if it had the lager air bell. The thin one is directly
off the blow off valve, the lager is on the pipe between the pump and
valve casting.
solution to building an engine from parts is to seek expert
help…..having said that beware some experts, and worse to assume
that a complete engine is built with all the correct parts.