<VV> Show and Tell - Show and Ask

[Dale Dewald]

On 8/11/2013 22:08, sethracer wrote:
> >>snip<<
> Yesterday, "Silicon Valley Corsa" and "Corsa - San Francisco Bay Area" had
> their annual joint picnic. No, we don't grill "joints", just meat. Ken
> Lawyer,  one of the members, brought along a piston/cylinder assembly that had
> "issues".  It is a .020 over L2206F forged piston. I am not sure how to
> describe the  damage to the piston -and the cylinder, pictures attached, but it
> looks like the  piston was hit with a Oxy-Acetylene cutting torch, just above
> and behind  the rings. It's a mess. It even cut into the cylinder. If you
> have a minute or  three, take a look at some of the pictures of the piston
> damage and see if you  can explain what happened? (This is the "Ask" part)
> Another picture shows  how the aluminum was blown into the inside of the
> piston, metal spraying. Cool  to see, unless it is your own piston, I guess. So -
> What happened?

It may seem far fetched, but if this is at the bottom of the cylinder I 
have a possible idea: thermite reaction. I speculate that the damage 
occurred upon starting the engine after sitting for an extended time. 
This piston was at bottom dead center with a valve open, directly 
exposing it to the atmosphere. Somehow a light film of rust formed on 
the cylinder wall but did not stick the rings enough to prevent 
cranking. The rust was scraped off as a powder when the engine was 
cranked,  collected at the cylinder bottom, and then was compacted into 
the lower face/edge of the piston and ring groove by contact with the 
head quench area. The subsequent firing of gasoline/air was hot enough 
to set off the thermite reaction. The cylinder pressure blew the 
reaction through the piston like a cutting torch.

Dale Dewald
Hancock, MI