<VV> Show and Tell - Show and Ask

[Mark Durham]

I agree with Bob. Pre-ignition. You can verify this by looking at your
plugs (check all of them, this cyl may be the worst, but there will be
signs on the other cylinder spark plugs and with this much stress in this
one, I would pull all cylinders and have a look) and comparing them to a
good plug chart. Check for color, the presense of metal on the ceramic of
the plug, and so forth.

I have dealt with many cylinders, corvair and aviation air cooled engines,
and although I've dealt with rust there has never been a problem where the
rust built up in a engine that would still turn over, it does work its way
into the oil and wreck havok with bearings, etc, but the worst I have seen
in the barrels are rust pits that hold oil. Even the most severe ones still
held compression unless the pits were at the top of the ring travel, but
the engines started to use too much oil because it was impossible for the
oil scraper to do its job.

While the oil does provide lubrication for the piston and rings, its
primary purpose is cooling. The ZDDP does the most protecting as it is
burnished into the metal surfaces constantly.

I'm running Egge .030 L2206-6's in my modified car and they are working
great.

Mark Durham
Hauser, Idaho
62 vair coupe red/red 4 speed

On Mon, Aug 12, 2013 at 9:07 PM, Dale Dewald <dkdewald at pasty.net> wrote:

> 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
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-- 
Mark Durham
Hauser, Idaho
62 Monza coupe Red/Red 4 speed