<VV> Lifters and other topics

[shortle]

And I wonder why the engineers chose to use hydraulic lifters instead of solid like our air cooled German brethen (whose initials I won't use this this forum to identify) also making compact cars. Was it for less valvetrain noise? Was it to reduce maintenance requirements? Was it cost (though I am certain solid lifters would be cheaper to make)? Come to think of it a lot of cars made back in the '60's used solid lifters.And I wonder how did the oil get to those valvetrains? Were those push rods also with small passageways?
Timothy Shortle in Durango Colorado


-----Original Message-----
>From: Sethracer at aol.com
>Sent: Feb 26, 2011 2:40 PM
>To: vairguy at echoes.net, virtualvairs at corvair.org
>Subject: <VV> 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
> _______________________________________________
>This message was sent by the VirtualVairs mailing list, all copyrights are the property
>of the writer, please attribute properly. For help, mailto:vv-help at corvair.org
>This list sponsored by the Corvair Society of America, http://www.corvair.org/
>Post messages to: VirtualVairs at corvair.org
>Change your options: http://www.vv.corvair.org/mailman/options/virtualvairs 
> _______________________________________________