[SEL] Engine bearings

Curt curt at imc-group.com
Thu Aug 16 13:00:29 PDT 2007


William Young wrote:
> I have acquired a medium power single cylinder American engine with bad bearings.  I will probably have babbitt con rod bearing made in USA.  My Japanese friend says aluminum bearings would be ok for mains.
>      What say you?  Anyone running an engine with aluminum main bearings? .
>
>
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William,
I would ditto Rob's comments and add a few too. Considerable effort was 
invested by the inventors of Babbitt to find just the right combination 
of the 3 soft metals (Cu, Sn, Sb) that would provide the necessary 
lubricity of the occasionally dry run bearing. Aluminum seem to loves to 
gaul (sp?) at the slightest provocation. Had aluminum been a decent 
bearing material, Babbitt likely would never have been invented. Once 
the TVA projects were in full swing and the like of Alcoa were going, 
their sales staff would have promoted aluminum for bearing material if 
it were a decent material for such.

I gather from your post that this small engine has replaceable inserted 
mains rather than poured ones. That said, aren't replacements available 
from Starbolt or other?

That said......

As a added point of discussion, aluminum case dengines (like Briggs and 
Stratton) appear to have the crankshaft running in direct contact with 
the aluminum case. They are always flooded in oil, different than our 
hit and miss engines. But none the less, why do these bearing last so 
well? I wonder if it could be related to a large cast grain structure as 
opposed to a fine grain structure the result of extruding or rolling of 
aluminum shapes.

Curt Holland
Gastonia, NC  boo hoo, wishing I were in Baraboo.



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