<VV> head repairs

Thu, 6 May 2004 13:57:49 EDT

Hi Mark,

You really don't want to put in a bushing as a fix for a number of reasons.  
Here's why.  The main reason that seats drop is because of the different 
thermal coefficient of expansion of steel and aluminum.  The aluminum expands more 
than the steel as the temperature goes up.  In effect, both the inside 
diameter of the hole in the aluminum and the outside diameter of the seat (or 
bushing) grow with rising temperature but the aluminum grows more.  The press fit 
weakens due to this effect.  The larger the initial diameter of these mated 
surfaces, the worse the problem is.  This is why the 140 heads have the worst pr
oblem with dropped seats.  The valves and seats are larger diameter than other 
heads.  Even though turbo heads get hotter, they have fewer dropped seats 
because of the smaller diameter of the seats.  If you put in an even larger diameter 
seat or bushing in a 140, you will almost guarantee another dropped seat.  If 
you rework the heads, you should have deeper seats installed or use the 
"Cromwell Method" that had a recent train here on VV.  In addition, this should be 
done to all of the seats on the assumption that if one seat has dropped, one 
or more of the others may soon follow.  

Good luck,
Doc
'60 Vette; '61 Rampside; '64 Spyder; '65 Greenbrier; '66 Corsa; '67 Nova SS; 
'68 Camaro ragtop
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In a message dated 05/05/04 6:45:03 AM Pacific Daylight Time, 
virtualvairs-request@corvair.org writes:

> Message: 7
> Reply-To: "Mark J. Murphy" <m.j.murphy@comcast.net>
> From: "Mark J. Murphy" <m.j.murphy@comcast.net>
> To: "Virtual Vairs" <VirtualVairs@corvair.org>
> Date: Wed, 5 May 2004 08:04:08 -0400
> Subject: <VV> head repairs
> 
> Thanks to all who replied to my search for a decent used 140 head.  I have 
> one in transit and hopefully should have her on the road again this weekend. 
> With that current emergency out of the way, I was thinking of fiddling with 
> the "bad" head to make a spare for when (I'd like to say "if", but...) another 
> seat drops in the future.  From what I can gather the accepted method of 
> fixing a head with a dropped seat is to weld in new alloy, machine the rebuilt 
> area back to factory specs and press in a new seat.  Is this correct?  Has 
> anyone tried machining the damage area out and pressing in an
> alloy sleeve as a bushing around the seat with any success?  I was thinking 
> about this as I don't have access to a TIG set, my welding skills are poor at 
> best, and at this point I have more time than money.  Any opinions?
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>       ,-----___\----,    Mark Murphy
>       \--(o)----(o)--'  Derry, NH, USA
>     http://m.j.murphy.home.comcast.net/
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~