"Nick Müller" wrote in message
...
Snag wrote:

Just to be pedantic: ;-)

My cue was that the originals were steel alloy . H-D had a reason
for that ...

There was a reason. Maybe without reason.


BTW , crank bearings are usually at least 2" diameter , and run with
an
oil film .

My example was only to show, that the bearing material itself doesn't
have to be thick-walled.

These are .674 and .699 diameter , and are greased . They also
only rotate about 10 degrees max , so the load is very concentrated .

The same is valid for bronce and steel bushings. :-)
Generaly, steel (gliding) on steel without _pressurized_ oiling is
deemed to fail. One exception coming to my mind is a CI-bushing.

Nick

There are tribology tables available that will show you which journal
materials work with which bearings, at which loads and which speeds; wear
ratios; performance with and without lubrication, etc.

From my diminishing memory, what I learned when I was reporting on this
subject is this: Mild steel on mild steel is one of the worst bearings
imaginable, at all but the lowest loads and speeds. OTOH, hardened steel on
hardened steel is one of the best. Before rolling bearings were available
for reasonable prices, hardened steel on hardened steel was used for the
most demanding instrument and machinery applications, including
ultra-precision grinders, at the highest speeds (then around 10,000 rpm for
an internal grinder, for example).

The bronzes are next, and work-hardening bronzes that get really hard from
work are the best of the bronzes. Aluminum bronzes and phosphor bronzes are
tops; phosphor bronzes being the older ones. Manganese bronze is next.

Aluminum and brass are actually quite good at low loads. Cast iron is an
excellent general-purpose bearing (bushing) material, handling quite high
loads, but all bearing manuals I remember reading say that it requires twice
the clearance of bronze. In applications where lubrication may fail, it is
the preferred material.

Where dirt is a problem or where the bearing may have to comply with a
less-that-rigid shaft, babbitt is the traditional favorite. It embeds dirt
and, given a thick film of lubrication, it has little tendency to gall (it
smears, but rather smoothly). Its specific wear ratio is poor, but that's
the tradeoff.

Galling is what kills mild steel and yellow brass. Hardened steel journals
running in mild steel bushings actually aren't bad if the loads are light
and the lubrication is good. The best hardened steel on hardened steel
bearings used no lubrication -- or, more accurately, they ran with dynamic
air bearings, with about a 0.001" clearance or less, down to 0.0002", and
had to run at high speeds because they dragged with air film around with
them ("dynamic" and "static" lubrication mean the opposite of what we
usually think).

Big breakthroughs occurred in bearings with, first, the Thinwall automotive
bearings introduced by a British company in the early '50s; then with
tri-layer bearings in the late '50s, and then with Honda's refinement of
tri-layer tribology, which they introduced on their 4-cyl. 750. It actually
had less friction than their earlier roller bearings.

It ain't sexy, but tribology can be really interesting. A lot of the
information about plain bearings that was gained at great expense,
empirically, is lost in the general literature and has to be dug up from old
engineering texts. But automotive bearing technology is very refined and
makes a good jumping-off point for understanding these bearings, and it is
the subject of continuing research and reporting.

--
Ed Huntress