<VV> RE: installing a cam?

[Doug Mackintosh]

I think you are both right!
   
  Rather than taking sides, I'll put on my engineer's hat to try to find and explanation that is consistent with the given observations.  
   
  I agree with Bob that a "tight spot" would have to be caused by either a bent crank, out of round journal, or gear runout/damage/trash problem. However, that does not preclude it being alleviated by case pounding or untorquing/retorqueing.
   
  If the crank is slightly bent (and all of them are, it's just a matter of degree), it will still turn freely if there is enough bearing clearance. Let's say the crank is bent enough to have .001" wobble. And let's say all the bearings have .002" clearance and are PERFECTLY aligned with each other (that is, bearing #1 is aligned with bearing #2, etc). Then the crank will turn freely. If the bearing clearances were .001" and perfectly aligned, we would be on the verge of binding (but I would expect uniform drag for all 360 degrees rotation). If the bearings had .002" clearance, but the center bearing was off from the end bearings by .001" you would now be on the verge of binding at one spot in the 360 degrees rotation. At 180 degrees from that spot you would have normal clearance since the crank and bearing alignment would both be misaligned in the same direction. In this example, it is possible that pounding the case and/or loosening and retorqueing could fix the problem
 by slightly changing the alignment of bearings to each other. Also, the effective diameter of the bearings will be smaller to the extent the case halves are misaligned at a given bearing.
   
  A similar explanation for a tight spot can be developed for an out of round journal and out of round bearing (or left half of a bearing not aligned with right half).
     
  <<
   
  Andy Clark said:
   
  "This is exactly what I experienced; a slight increase in drag at the 
same
spot on every revolution."
   
  While Bob Helt said:
   
  > This must be caused by the crank, and only the crank,  or some  
attachment
> (eg, a gear) to the crank. Only the rotating device can cause this
intermittant
> drag. If it were the crankcase, or a function of the torquing  
sequence,
then
> something would be out of alignment. This would cause a STEADY  
increased
> drag. In other words this would contact the crank in a uniform 
manner,
pressing
> on it and increasing the drag, but in a constant manner.



-- Doug Mackintosh
  Corsa member since 1996
  Corsa/NC member since 1996,  Virtual Vairs member
  Corvair owner 1969-1971 and 1996-on
       
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