engines other than those in the late RMFs and RMHs (Pathfinders) have
white metal bearings instead of more modern replaceable shell bearings.
As many owners have found over the years these can fail and the first
thing the driver notices is a loud knocking from the engine.
In almost all cases where an engine has covered a high mileage
caused by a lubrication failure due to blocked oil ways within the
crankshaft. In some cases it can be due to a previous poor repair
leading to failure of the white metal to adhere properly to the
connecting rod. If this happens the failure may look like the
one shown below where part of the white metal has pulled away from the
connecting rod cap. If this happens in a recently rebuilt engine
take it back to whoever did it and complain. It was probably due
to either the connecting rod not being preheated correctly before the
white metal was poured or the surface of the connecting rod not being
Handbook says under
routine maintenance that the sump should be removed for cleaning every
10,000 to 12,000 miles but how many owners actually do this?
owners change the oil and oil filter believing this is all that is
really necessary. Unfortunately neither the Driver's Handbook
the Workshop Manual makes any mention of the need to clean out the
sludge traps in the crankshaft so even those owners who do clean the
are not immune to disaster.
Workshop Manual shows the lubrication system for the 2½
engine. Unfortunately it is not a very clear diagram but it
be seen that the big ends are fed with oil from the main bearings.
Oil from the main bearings passes through drillings in the
crankshaft into a chamber within the crankpin journal which is the
sludge trap. From here it is fed to the big end bearing
When the Riley 9 was introduced in 1927 it
did not have an oil filter. To keep the oil clean it was
centrifuged by the crankshaft and the heavy particles were retained in
the sludge traps in the big end journals. Cleaning out these
traps was part of the maintenance schedule. Later engines based on the
Riley 9 design such as the RM engines were fitted with oil filters but
the sludge traps remained although no mention was made in the
documentation of the need to clean them out regularly.
Presumably it was thought that the oil filter would trap all
the sludge so cleaning out the sludge traps would not be necessary -
how wrong this has proven to be. As the RM crankshaft spins
the sludge within the sludge traps gets compacted into a solid lump.
Eventually there is so much compacted sludge in the trap that
it covers the feed hole to the bearing and starves it of oil leading to
big end bearing failure and the dreaded big end knock.
diagram of the RMB crankshaft shows the big end plug as fitted to No. 1
big end journal. It can be unscrewed with a large hexagon key
and the trap behind it can be cleaned out. After being
undisturbed for many years it is often found
impossible to unscrew the plug and it has to be drilled out. This
cannot be done with the crankshaft in place so it has to be removed
from the engine which in turn means that the engine has to be removed
from the chassis. Although this can involve a lot of work the
need to clean out these sludge traps cannot be over stressed and there
is no point in repairing the bearings if this is not done as the new
bearings will fail very quickly for the same reason that the previous
picture we can see No. 4 big end journal with the big end plug removed
and resting on the crankshaft. Next to it is a slug of
compacted sludge (arrowed) removed from one of the other journals.
compacted sludge remains within No. 4 journal and is compacted
sufficiently to support a length of welding rod pushed into it.
This is an RMF crankshaft so the claim that the problem was
overcome by a modification to the to the big end
oil ways in the RMF crankshaft is clearly not true.
how can the big end bearings be repaired? There are two
possible solutions. The first is to have the connecting rods
remetalled by a specialist workshop. The workshop will need
to regrind the crankshaft journals to remove any scoring and to ensure
that they circular. Wear to the journals will result in them
being slightly oval. The remetalled connecting rods will have
to be machined to fit the reground journals. An advantage of
this method is that very little metal will need to be removed from the
crankshaft. Finding a workshop which can recast white metal
bearings is becoming increasingly difficult as it is a skilled
operation. An Internet search is a good place to look for a
workshop near to you but be sure to check their reputation and how long
they have been in business. If possible talk to someone who
has had work done there. In the past there have been
workshops who have produced poor quality work resulting in the new
bearings breaking up quickly.
solution is to convert the connecting rods to accept shell bearings and
regrinding the crankpins to suit the new shell.
Before doing this check that shells will be available to fit
the reground crankshaft. A disadvantage of this method is
that each time new shells are fitted and the crankshaft is reground, 10
thou. will need to be removed from the journals and there are a limited
of shell sizes available. A workshop repairing
should be able to do this repair as no white metal casting is needed.
information on this subject and for details of the repair procedures
please see our Maintenance
This gives a full description of the lubrication system
oil pump, details of the crankshaft and its suitability to accept shell
bearings, the bearings themselves, engine removal, engine dismantling,
checking for wear and damage, journal and bearing repair and
refurbishment, how to convert to shell bearings and finally how to
prevent the sludge traps filling up in future.