<VV> adjusting valves - I want to believe!

[The Reinharts]

Guys, Don't forget steel expands at a different rate than alum. I believe it 
is .002 per inch of diam. or lenghth from 70F to 200F according to my tool 
makers handbook. Very interesting discussion.

Jamie
Toolmaker for 10 years
----- Original Message ----- 
From: "James Davis" <jld at wk.net>
To: "Craig Nicol" <nicolcs at aol.com>; <virtualvairs at corvair.org>
Sent: Monday, November 03, 2008 07:27
Subject: Re: <VV> adjusting valves - I want to believe!


> Looks good to me.  I stand corrected.
> Jim Davis
>
> At 11:23 PM 11/2/2008, Craig Nicol wrote:
>>Jim wrote:
>>A little math is in order.  The threads on the rocker studs are
>>3/8-24, so each turn of the adjusting nut is 0.0417 inches.  Since
>>the slack take up is on the pushrod and valve tip at the same time,
>>the adjustment is 0.0833 inches each turn.  The the adjustment range
>>in most lifters is 0.180 to 0.200.   The engine grows about 0.006
>>inches for each 100 degrees Fahrenheit.  So now you can make an
>>informed decision as GM did.
>>Jim Davis
>>
>>Craig replies:
>>I like where you are headed with this, Jim!  I do have a little correction
>>to consider.
>>
>>The notion that a turn of the adjustment nut causes .0833" at the pushrod 
>>is
>>possibly incorrect; here's my thinking:  I don't think the adjustment nut
>>equally affects the valve stem and the pushrod as you stated.
>>
>>The valve stem does not move when the adjustment nut is turned, the valve 
>>is
>>stationary and is effectively the fulcrum of the lever.
>>
>>The rocker supposedly has a 1.58:1 ratio but let's imagine for a second 
>>that
>>it was a 1:1 ratio, which would put the adjustment nut in the exact 
>>middle.
>>At THAT ratio, .0417" movement at the nut would cause .0834" movement at 
>>the
>>pushrod. To simplify the math for our actual ratio, consider for a moment
>>that the rocker arm ratio was 3:1. In that case the pushrod would move 4/3
>>the distance of the nut movement. (4=overall units of length, 3=units of
>>length at nut, relative to fulcrum, hence the 4/3 effect)
>>
>>At the actual ratio of 1.58:1, the overall units of length = 1+1.58 (or
>>2.58) so using the same concept as the 3:1 example, the pushrod would move
>>2.58/1.58 (1.63) times the nut movement. Using this factor, I think a 
>>.0417"
>>movement at the nut would cause.060" movement at the pushrod. (.0417" x 
>>1.63
>>= .060") rather than the .0833 you calculated.
>>
>>Here's how that shakes out:
>>
>>1/4 turn = .015 at the lifter (ignoring the pushrod angle to the lifter) 
>>In
>>an environment where the engine grows .006" per 100 degrees and the lifter
>>has an available range of .180 to .200., this theoretically doesn't offer
>>enough lifter stretch for higher engine temperature and uses very little 
>>of
>>the lifter's range. (.15" out of .100" to center of lifter's range)
>>
>>1/2 turn = .030" (which should accommodate a 500F degree engine temp 
>>change
>>but still uses only a fraction of the available .100" "center of lifter
>>range")
>>
>>3/4 turn = .045", not even halfway to the center of the lifter's range, 
>>but
>>clearly able to accommodate well beyond any conceivable engine growth.
>>
>>1-turn = .060", still well short of the lifter's center of range.
>>
>>I'll also add observations that the more the preload there is the less 
>>time
>>it will take a collapsed lifter to refill and the less time it will take 
>>for
>>the pushrod to fill and deliver oil to the upper valve train; both worth
>>considering.
>>
>>So the questions are: Why does 1/4 turn seem to work so well?
>>
>>If the preload is set to 1/4 turn when cold, according to this analysis it
>>should clatter when hot. Perhaps 1/4 turn works only if adjusted at
>>operating temperature. I wonder if this unspoken need to have the engine 
>>at
>>temperature is why we hear so much cold/hot, 1/4 turn-1/2 turn-1-turn
>>controversy?  Maybe 1-turn is the right answer if valves are adjusted cold
>>and 1/2-1/4 turn is the answer if adjusted hot.
>>Craig Nicol
>>
>>Note to math wizzes (which I am not): please check my math on the effect 
>>of
>>the rocker arm ratio when the fulcrum is changed to the end when the ratio
>>calculates to 1.58:1 with the fulcrum is at the middle. ;-)
>
>
>
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