<VV> lead additive - more info

[Sethracer at aol.com]

In a message dated 9/4/2007 8:22:19 A.M. Pacific Daylight Time,  
corvair at fnader.com writes:

Actually, while that may be true for certain understressed American  
V8's, it's not a valid blanket statement. Some cars exhibit quick and  
severe valve seat recession (a late model UK car I had even announcing  
in the owners manual in huge red letters "Under NO CIRCUMSTANCES should  
this vehicle EVER be operated on unleaded  petrol".)




A little more elaboration - By 1971, all of the US manufacturers knew  of the 
upcoming ban on Leaded gas, due to the catalytic converters. They had  
already changed their production techniques to use induction hardening of Valve  
seat areas (interesting process to watch, by the way) on their cast iron heads.  
Those motors should be fine. It is the older motors, 50's and 60's, that had 
the  problems. I have not seen the Buick study, but here is a Googled  FAQ from 
 a gasoline web site (probably British):
 
 
8.9 How serious is valve seat recession on older  vehicles?
The amount of exhaust valve seat recession is very dependent on the
load  on the _engine_ 
(http://stason.org/TULARC/vehicles/gasoline-faq/8-9-How-serious-is-valve-seat-recession-on-older-vehicles.html#) . There have been 
several major  studies on valve
seat recession, and they conclude that most damage occurs  under
high-speed, high-power conditions. Engine load is not a primary  factor
in valve seat wear for moderate operating conditions, and low  to
medium speed engines under moderate loads do not suffer  rapid
recession, as has been demonstrated on fuels such as CNG and
LPG.  Under severe conditions, damage occurs rapidly, however there are
significant  cylinder-to-cylinder variations on the same engine. A 1970
engine operated at  70 mph conditions exhibited an average 1.5mm of
seat recession in 12,000km.  The difference between cylinders has been
attributed to different rates of  valve rotation, and experiments have
confirmed that more rotation does  increase the recession rate.
The mechanism of valve seat wear is a mixture of  two major
mechanisms. Iron oxide from the combustion chamber surfaces adheres  to
the valve face and becomes embedded. These hard particles then  allow
the valve act as a grinding wheel and cut into the valve seat. 
The significance of valve seat recession is that should it
occur to  the extent that the valve does not seat, serious engine
damage can result  from the localized hot spot.

There are a range of additives, usually  based on potassium, sodium or
phosphorus that can be added to the _gasoline_ 
(http://stason.org/TULARC/vehicles/gasoline-faq/8-9-How-serious-is-valve-seat-recession-on-older-vehicles.htm
l#)  to combat valve seat  recession.
As phosphorus has adverse effects on exhaust catalysts, it is  seldom used.
The best long term solution is to induction harden the seats or  install
inserts, usually when the head is removed for other _work_ 
(http://stason.org/TULARC/vehicles/gasoline-faq/8-9-How-serious-is-valve-seat-recession-on-older-
vehicles.html#) , however additives 
are routinely  and successfully used during transition periods. 




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