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

[RoboMan91324 at aol.com]

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