Join Date: Nov 2009
Location: georgia's toe-nails of the foot hills
Re: Piston Corrosion On HH100
Check the piston ring end gap by placing them in the bore, one at a time, and using the piston backwards to push a little on the ring, square the ring. Measure the gap between the ends of the ring using a feeler gauge. Check against the manufacturer specified range. If within tolerance, pbt. The rings are allowing blowby from the combustion chamber to pressurize the crankcase, causing the oil to get blown out. At higher rpms, the pistons seem to seal better in most cases as there is not enough time for the gas to escape past the rings into the crankcase. You'd see a lot more at idle speeds in most cases.
The top of the piston sure looks clean compared to a lot of the pics you see posted here. From the condition, it is hard to believe this engine is blowing oil. Most times the piston would be covered with 'stuff'. The rod bearing is not perfect, but I have yet to see one that has run for any length of time that IS perfect. What does the crank journal look like?
The scoring of the topmost land is a little more than expected. Was it run low on oil or with the cooling fins clogged with trimmings? If the piston fits into the bore without binding, and doesn't flop around, as in you cannot 'rock' it, then you can put back together and see what happens. If you are doing this for a living, the more profitable and likely success will be found with new parts. If you are on your own time, you can afford to try the old parts. Check to see how sloppy the rings are in the grooves by sticking the ring into the groove 'backwards' and using a feeler gauge to measure clearance between the top or bottom of the ring and the land. There is a spec for that too. If the clearance is too large, the ring will have too much room to flop around, and will not seal properly. I think it will 'flutter' in the groove rather than follow the piston smoothly, leading to poor sealing.