The camshaft is something like 270-272*. We should really tear down the engine to see if the .009" piston to cylinder wall clearance is necessary or not. The ring end gap was also getting big with the extra piston to cylinder wall clearance.
Are you making your own pistons now? If so wouldn't be surprised,lol !
Thats my only other worry about my current pistons ,the ring lands. Never had an issue without having the steel ring land insert on the diamond pistons. They were not used in a "daily driver" application and would never see any measureable wear.
In my other engines (with ARL pistons) I've been running .004" p/w clearance, and that was enough to bring the ring end gap out to .025" or so, wide but safe.
Figured that .006" piston/wall is about equal to the .009" that the real hot cummins B series guys run when you account for the much smaller piston diameter. Thermal expansion is an "inch per inch" figure, after all, and they lack the oil channels in their pistons that the higher end TDI pistons have for better cooling.
Actually recently started experimenting with running bottom of the barrel ALH/AHU/1Z pistons, used to be fixated on the ARLs with the properly lowered ring lands but the finns have got me enticed with the draw of not spending a thousand dollars on pistons and rods in every engine I build, hah. I'm unsure about cutting deeper valve reliefs in the ALH pistons however, with their rings only being 1/4" below the piston crown rather than the 1/2" of the ARLs.
The issues I was having were the from the (stock 300k mile clearances) top rings butting and breaking, the secondary ring land has only 1/8" or thereabouts of aluminum between it and the oil ring, so thinking on it a bit more critically, of course it pushed down into the oil ring's groove when forced to take up the slack of the broken top ring. An aluminum ring land with more meat underneath it would likely be much more durable.
