I did a rings and valve grind on my 89 TW. I honed the cylinder, assembled everything carefully with anti-seize compound or coated with oil, torqued to specs, put it in and filled with oil, bled the air out till it was pumping oil out, and as far as I know, all to the book. I started it and let it idle a bit on the stand, then took it for a gentle ride around the country block at about 40 miles an hour. I never made it home. At 12 miles it clattered and quit. I pulled the cylinder, and the piston is fried, as if it had no oil, but the oil is up. The little holes that let oil through from the inside of the piston to the cylinder wall were open, the oil filter seemed fine, and had collected some filings. I just can't wrap my head around it. TW brain pool, what do you think?