Unfortunately, the camshaft bearings on the Duo-Art Steamboat pump are
not adjustable.  If the pump is knocking, it is because it is worn out.
The bearings are supposed to be oiled and will wear out, especially on
the loaded driven side, if this is not done.

It is also possible that the shaft is worn.  The cams are pinned on the
shaft, and it is not a good idea to replace the shaft or remove the
cams for any reason, since the pin holes were drilled in place.  So it
is best to turn the shaft between centers on a lathe, if it is worn.
Replacing the bearing is not a big deal for a good machinist; but you
need a big lathe to resurface the shaft without removing the cams.

The original belts were leather and were tensioned with a roller
running on the back side of the belt. This worked well on leather
belts.  But rubber belts are generally not made with much attention to
their back side (not much attention to the drive side either on many
belts); so it is almost impossible to get proper tension with the
idler.  I have also seen Steamboat pumps with a considerable amount of
runout on the large pulley.  This can also make it difficult or
impossible to get the belts properly tensioned, as they will be tight
and loose alternately as the large pulley moves up and down.

It is also necessary to use matched belts, although there is really no
reason other than aesthetics to use four.  Four belts were helpful when
running leather belts, since they do not have as much grab unless a
belt dressing is used, which is why you often see all sorts of goop on
the old leather belts.

Using a matched pair of good rubber belts might put enough tension on a
worn bearing to make it quiet down.  Use a good synthetic oil to help
reduce further bearing wear. A couple of urethane belts made with a
fair amount of pre-load (they will stretch in time and may need to be
shortened again) also can help to compensate for a worn bearing.

Another possibility would be to use modern bearing material such as a
reinforced PTFE.  That material is much easier to machine and somewhat
forgiving.  If the shaft is not in good condition, the bearing will not
last very long.

Spencer Chase
http://www.spencerserolls.com