How does sand get into an engine?
 

Here are the pics of the sand
 

These pics were taken just after I pulled the head of an "extra" engine...

Pistons are frozen solid... how do I lose them? Is it worth saving?

What do you think?



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pour marvels mystery oil in and let sit for a few days. Then try to remove the loosened crap from the bores and take a block of wood and try to tap the pistons down to free then up.

+1 but instead of MMO I'd use a thin penetrating oil, diesel or kerosene at first, then use something thicker.
Hopefully they'll come out without scratching the **** out of the bores.

And to answer your original question, it looks like sand, but its a combination of carbon, moisture, and any other crap we get out of the low quality fuels we are compelled use, even when we pay top dollar for higher octane juice. Just look at the crud that builds up on spark plugs. I guess, it is more than likely sand, from somewhere in Arabia! :) oops, should I have said that?

I would just rebuild the entire engine being it is out of the car and practically dismantled. The corrosion is a combination of old coolant, natural minerals from poor water and degraded gasket material as well as some dirt/sand. Use a soft plastic polishing wheel to remove the carbon via a hi speed drill/dremel.....Or take it to a machine shop and let them run it through their cleaning process.

Dal

If those pistons are frozen solid... There may be other issues. I'd be pretty hesitant to pound on the cylinders with anything. Scratch the cylinder bores and you're buying a new set. And Alusil cylinders like those are not cheap. Actually, it might be better to just replace in the process of your rebuild.