as the piston came up compared to the one next to it at TDC. Oil pan is off, ALMOST have the head off, but broke the 10mm bit trying to remove the head studs. One came slightly loose then second one broke the bit. So far diagnosis is consistent and plan is to check bearings, crank shaft on #6. If all good, hone cylinder, replace rod, rings and piston and go back together. Going to get bigger tools tomorrow.