<VV> 110 vs 140 Heads (Dropped/Popped Seats)

[MarK Durham]

Doc, great engineering explanation!
Mark Durham Hauser Idaho.
On Mar 25, 2014 10:23 AM, <RoboMan91324 at aol.com> wrote:

>  Hi Mark,
>
> You may have touched on part of the reason but I would like to expand on
> the issue, if I may.  No pun intended.  :-)
>
> There are many factors involved that contribute to dropped seats and the
> size of the valves and seats in 140s is one of them.  Related to the higher
> temp, it has to do with the thermal coefficient of expansion (TCE) of
> aluminum vs. that of the seat material.  The formula used for the TCE in
> English units is in Inches per Inch per Degree Fahrenheit.  The "per degree
> F" portion is self explanatory in that the hotter any substance gets, the
> larger it grows.  (With one notable exception during change-of-state.) The
> "inches per inch" part of the formula may need some explaining.  I find
> that exaggerating the phenomenon helps to understand it.  If you have a
> substance that grows 1 inch for every degree rise in temp and the cool
> dimension starts at 1 inch, it will grow to 2 inches with a 1 degree rise;
> 1 inch growth.  If you have the same substance that starts out with a 2
> inch cool dimension, the same 1 degree rise in temp results in a 4 inch
> piece of the substance; 2 inches growth.  Now transfer the concept to the
> different size valves in 140s vs. all other engines.  Because the 140 valve
> seat starts out at a bigger dimension, it will grow larger than the 110
> (for instance) valve seat with the same temp rise.  Now for the crux of the
> matter.
>
> You say that the seat will also get hot and expand so what does it
> matter?  Well, the TCE of aluminum is nearly twice that of steel.  I.E.;
> the aluminum head will grow much faster than the steel valve seat with the
> same temp rise.  This tends to reduce the press fit (or compression fit or
> interference fit) of the valve seat to head contact.  Using exaggerated
> dimensions again; if the TCEs of aluminum compared to steel are 2:1 and the
> inside diameter of the valve seat hole in the aluminum grows 1 inch, the
> outside diameter of the valve seat will only grow only 1/2 inch.  In this
> exaggerated example there will be a 1/4 gap between the head and the seat
> all the way around and the seat will start banging around until it beats
> the head and itself to death.  This is the effect of differential TCE.
> Keep in mind that the real TCE of the substances stated above are much
> smaller in the real world but the net result is that press fit will be
> diminished.
>
> When assembling seats into heads, the heads are heated to a high
> temperature but still below the point that its material characteristics
> change.  Also, the seat is frozen before assembly.  Because of the TCE, the
> hole on the head gets larger and the seat gets smaller before assembly.
> After assembly, they quickly reach the same temp with the aluminum
> shrinking around the seat and the seat expanding into the hole in the
> head.  Interference fit.
>
> With either large or small valve heads, a large temperature rise can
> result in disaster.  However, because of the larger diameter of the 140
> valve/seats, they are at greater risk.  Also, because of the higher
> compression ratio and usual higher energy development in the 140s the temp
> tends to rise more than in other engines and that further aggravates the
> situation.  Turbo engines are an exceptional situation.  When they go into
> boost, the temps rise very quickly and the smaller valve seats are at
> greater risk than the larger 140 seats.  You can get a thermal runaway in a
> turbo and trash it before the danger shows up on your temp gauge.
>
> Because of the length of this message, I won't go into detail but under
> certain operating conditions, a hot seat could be quenched with a cooler
> air/fuel mixture which tends to shrink the seat thus reducing the press fit
> further.
>
> Now add in the fact that our engines are quite old and they have suffered
> many hot/cold cycles and sometimes serious overheating on occasion.  The
> aluminum may have lost some tempering which reduces the press fit.   While
> many 140s and turbos suffered problems early in their lives, now with age,
> lower HP engines are failing more and more.  Also, like all manufacturing
> processes, there may have been variations of fit from head to head and even
> from seat to seat in the same head which puts one engine at greater risk
> than another from birth.
>
> So, the point to all this is that you should try to run your heads as cool
> as possible.  Lightening your lead foot helps but a guy has to do what a
> guy has to do, right?  Keep in mind that, if you have a temp gauge, it
> measures only at one point on one head unless you have multiple sensors.
> The temp of the head at another point can be significantly different and
> the head on the other side can be doing something completely out of
> control without any indication on the dash until your RPMs drop to zero.
> Whether you have a low HP or a high HP engine, ALWAYS deflash the heads as
> necessary when you get the chance.  Your oil is a source of cooling for the
> heads too so do what you can to keep that cool as well.  A poorly tuned
> engine can also invite thermal problems.  Knock/pinging is to be avoided at
> all costs.  It will heat and beat your engine to death quickly.
>
> If you have the money and definitely if you will drive the car hard,
> consider installing deep seats especially on 140s, 150s and 180s.  If you
> are going to try something strange like using a big valve head with a
> turbo, you absolutely must know what you are doing or you will be riding
> home in the cab of a tow truck.
>
> Doc
>  1960 Corvette, 1961 Rampside, 1962 Rampside, 1964 Spyder coupe, 1965
> Greenbrier, 1966 Canadian Corsa turbo coupe, 1967 Nova SS, 1968 Camaro
> ragtop
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  In a message dated 3/25/2014 7:46:48 A.M. Pacific Daylight Time,
> virtualvairs-request at corvair.org writes:
>
> Message: 2
> Date: Mon, 24 Mar 2014 17:37:25 -0700
> From: MarK Durham <62vair at gmail.com>
> Subject: Re: <VV> 110 vs 140 Heads
> To: Frank DuVal <corvairduval at cox.net>
> Cc: virtualvairs at corvair.org
> Message-ID:
>     <CAEEoEu54BANBvkD8ErOH9U_M83GUdy98RobNs-nB2dgGOiu9mA at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Its just that the small valve heads have a lot less problem with dropped
> seats than the hotter running 140 heads. I do not know the dynamics of why
> that is other than the 140 heads have a larger intake runner and larger
> valves and larger exhaust tubes so they can flow more air/fuel mixture and
> produce more power and the result is its easier to put them over the edge
> when less than ideal hot conditions exist.  Mark Durham Hauser Idaho
>
>