<VV> Lifters and other topics

[Mel Francis]

The same chief engineer who designed the Chevrolet V8, designed the Corvair 
engine.

Automatically-adjusting hydraulic lifters work especially well, with the 
greater change in overall
size of an air-cooled engine during very cold to very hot engine cycles. 
Cost wasn't a factor, since
Chevy was already producing millions of them for V8 production.

Mel


----- Original Message ----- 
From: "shortle" <shortle556 at earthlink.net>
To: <Sethracer at aol.com>; <vairguy at echoes.net>; <virtualvairs at corvair.org>
Sent: Saturday, February 26, 2011 6:18 PM
Subject: Re: <VV> Lifters and other topics


> 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
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