Rich Replies

[Bob Lorenzini <hwm@netcom.com>]

>On the other hand, Peter Krause wrote:

>>P.S. Rich in CO, you are GREAT entertainment! Tell me again, it was the
>>higher combustion temp caused by  a "rich" mixture that caused Rob
>>Dyson's R & S Mk III two pistons to melt leading the Daytona 24
>>Hours?!?!

  Rich your credentials as an engineer and race car driver are very
impressive so I'm somewhat perplexed that you refuse to believe that
running too lean does not burn pistons and valves. Please forgive me if
this is not the case as I don't remember who it was that held this view.
Like Peter Krause I question your practical experience as this has been
common knowledge for as long as I have been around engines (50+years) as
a backyard hacker and occasional racer.  

A quick search on the Internet turns up:

From Shell Oil Company

Burned Piston
                When a cylinder runs lean (too much air in the air-to-fuel
mixture) and excessive heat burns or melts the piston.


BY ERIC GORR edited to the relevant portions by me

  The process of examining a used piston can tell a mechanic helpful
information on the condition of an engine. When an engine failure occurs,
the piston is likely to take the brunt of the damage. A careful
examination of the piston can help a mechanic trace the source
of a mechanical or tuning problem. This technical article serves as a
guide for the most common mechanical problems that plague engines. 

ASH TRASH

  This piston crown has an ash color, which shows
  that the engine has run hot. The ash color is
  actually piston material that has started to flash
  (melt) and turned to tiny flakes. If this engine was
  run any longer, it probably would,ve developed a
  hot spot and hole near the exhaust side and failed.
  The main causes of this problem are too lean carb
                                      ^^^^^^^^^^^^^  
jetting, too hot spark plug range, too far advanced
^^^^^^^
  ignition timing, too much compression for the fuel's
  octane, or a general overheating problem. 

BURNT-OUT BLOW-HOLE

  This piston was overheated so badly that a hole
  melted through the crown and collapsed the ring
  grooves on the exhaust side. Normally the piston
  temperature is higher on the exhaust side so
  catastrophic problems will appear there first. There
  are several reasons for a failure like this, here are
  the most common; air-leak at the magneto side
  crankshaft seal, too lean carb jetting, too far
                   ^^^^^^^^^^^^^^^^^^^^^^
  advanced ignition timing or faulty igniter box, too
  hot of a spark plug range, too high of a


Bob Lorenzini
84 spyder (bastardized)