From: rod@sadtler.com (Rod Farlee)
Newsgroups: rec.aviation.owning
Subject: Re: What's TCP (Was: Fresh Overhaul & Mobil 1)
Keywords: engine overhaul synthetic oil tiger
Date: 6 Nov 92 05:31:59 GMT
Organization: Sadtler Research Laboratories

Although there have been several replies to the question:
> What's TCP?
here's a trivia note: use of TCP tricresyl phosphate, was discon-
tinued in 1990 due to health concerns.  It was replaced with TPP 
triphenyl phosphate.    

      HC = CH               HC - CH
      /     \               //   \\
 R - C      C - O - P - O - C     C - R
      \\   //       |       \    /
      HC - CH       O       HC = CH
                    |
                    C
                  //  \
                HC     CH         TCP: R is CH3
                 |     ||
                HC     CH         TPP: R is H
                  \\  /
                    C
                    |
                    R

TPP has very similar properties, but there is some doubt about its 
effectiveness.  Both are toxic and corrosive, and should be handled 
with gloves and good ventilation.  

Shell 15W50 and Phillips 20W50 include TPP as an EP extreme pressure 
additive.  Marvel Mystery Oil contains phosphorus, presumably as TPP.  
Lycoming sells TPP as LW-16702, and Alcor as "TCP".  

Contrary to one previous posting, TCP affects neither the octane 
rating of gasoline, nor the viscosity index of oil.

TCP is an EP extreme pressure additive for oil:
On the cylinder head walls, TCP reacts with clean steel surface
to form a soft iron phosphate monolayer.  The rings tear this 
soft monolayer off during each power stroke, thereby reducing wear
to a single atomic layer of iron, instead of ripping several layers 
of unprotected steel.  It has the same reaction on Lycoming camshafts,
which are not otherwise lubricated during cold starts.  Its use is 
recommended in Lycoming Service Bulletin 446C to deter camshaft 
scuffing during start-up and initial cold running.

Aircraft engines are intentionally designed to burn oil, and steel 
cylinder head walls are designed to wear out, in about 8000 hours.

Unlike the EP additives used in automotive oils (zinc dithio-
phosphates), TPP is ashless and does not erode silver alloys used 
in certain Continental front-end and Lycoming supercharger bearings.

TCP can be used as a lead scavenger additive for fuel:
TCP is more volatile than ethylene dibromide, so is better 
distributed to all the cylinders by the induction system of 
carbureted engines.  (Lead is not an octane enhancer; it is the 
ethyl radicals formed by the thermal decomposition of tetraethyl 
lead that are the octane enhancers.  These combine with radicals
from fuel, thereby quenching spontaneous combustion, or detonation.)  
During combustion, TCP reacts with lead to form a soft lead 
phosphate, which can be blown out the exhaust, rather than forming 
a hard lead oxide deposit sticking to the spark plugs, valve guides, 
etc.  

Sorry for all the trivia, but sometimes technicalities get a bit
hazy in rec.av.  Remember Netiquette #6, friends: "Look things up."
-- 
Rod Farlee, rod@sadtler.com, (215) 382-7800
Bio-Rad, Sadtler Div., 3316 Spring Garden St., Philadelphia PA 19104
Newsgroups: rec.aviation.owning