[TheForge] Re: A&O

[theforge@mailman.qth.net]

Harley's use a needle bearing in the bottom end ( very similar dynamics 
to a compressor).  At least the Shovel heads and earlier models.   I 
have never worked on a Evo or Dyna.  Needle bearings can be pounded out 
of round, at which point they wear quickly.    It is interesting to note 
that almost all piston engines use shell bearings rather than needle or 
ball bearings.    Out of curiosity, I looked it up in a few of my 
Internal Combustion Engineering texts and it seems that the primary 
reasons shell bearings are prefered are because: 
 
A) They are perfectly adequate
B) They are simpler to install ( a harley require dissassembling the 
entire crankshaft to replace the bearing.  doable since it has only one 
crankpin)
C) They are cheaper to manufacture and install.  

For antifriction bearings(ball,roller and needle), it lists the 
following advantages:

A)  Require less lubrication
B)  Less axial space required, although generally a larger diameter is 
required
C)  Starting friction is less

Disadvantages are listed as:

A)  Assembly, as noted above is much more complicated
B)  More subsceptable to corrosion, with a very short life once encountered
C)  Bearing failure is more sudden, more disastrous and with less warning.
D)  Unit cost is higher, and generally labor is higher.



  

Andrew Vida wrote:

>Mike Spencer wrote:
>
>  
>
>>In this case, I don't thing shock is an issue.  It's a compressor,
>>right?  It's turning 180 rpm (? I forget...) and mooshing air.
>>    
>>
>
>	The bearing undergoes large spikes in stress when
>	the crank throw reaches top- and bottom dead center.
>	
>  
>