<VV> Lifters and other topics

[Ray Rodriguez III]

A perfect reply, just what I was looking for thank you Seth!

Ray R.
  ----- Original Message ----- 
  From: Sethracer at aol.com 
  To: vairguy at echoes.net ; virtualvairs at corvair.org 
  Sent: Saturday, February 26, 2011 4:40 PM
  Subject: Lifters and other topics




  In a message dated 2/26/2011 12:33:51 P.M. Pacific Standard Time, vairguy at echoes.net writes:
     I also don't see how the tappet being flat would really make such a major difference, and if it did it seems all it would do is wear the lifter and/or pushrod which are easy to adjust and fairly easy to replace. So please enlighten me!  

         I'm not trying to argue the point, I'd just like to be educated in the mechanics involved.


  The "Tappet" is just another name for the "lifter" and they can be solid or Hydraulic. The cup end holds the pushrod and the movable, internal plunger, is kept in place by a clip or spring. Internally, the lift acts as a passageway to feed oil from the gallery, located in the case on the Corvair, up the pushrod to lubricate the valve spring and the rocker. The hydraulic lifter also uses this oil - fed under pressure by the engines oil pump - to take up the clearance, by pushing up the plunger, in the valve train to help provide quiet operation. A solid lifter engine, in order to allow for the growth of metal under temperature change, has to have extra clearance pre-set in the valve train to make sure the valve can close - absolutely - when hot. If no clearance was pre-set, the growth of the dimensions of the parts would hold the valve open causing mis-fires. Most engines have gotten away from solid lifters because the noise can be distracting (Let me tell you about a Duntov .030" inch clearance cam I had in a Corvette! You could hear me coming for blocks) Almost all Corvairs have hydraulic lifters - a few racers have installed solids. Flat tappet cams are called that because they present a flat face on the bottom of the lifter to ride against the lobe of the cam. Roller lifters present a cylindrical mounting interface. In both cases, a line of material contacts the cam. That line, in theory, changes as a roller cam follower spins at the bottom of the lifter, and in a flat tappet system, the cam is ground with a slight taper which is supposed to "spin" the lifter around a bit during operation. Most importantly, a flat tappet lifter presents a heavier (as in lbs per square inch) wiping contact load against the cam, than a roller lifter. It is generally regarded as the highest load applied to any surface inside the motor. The wear on this surface is mitigated by the oil on this surface and the "high-pressure" additives of the oil. The ZDDP - essentially a zinc-phosphate compound, provide a cushion in that load. Supposedly that compound is a contaminator of the catalytic converter on modern cars so it is being removed - or greatly reduced on new-car oils. Thus the controversy for older cars that, supposedly, need that assistance on their flat tappets. Almost all new cars have roller tappets for several reasons. Wear on the tappet to lobe quickly results in low or no valve opening, not good for performance. And the cam, far from being easy to replace, is just about the last thing that falls out of the motor when you disassemble it.  

  Seth Emerson