This machined piston, made from Mahle 138 bar stock, clearly shows the upper end guidance of the connecting rod. A total clearance of .003 to .005 keeps the rod centered in the engine. A total of .0001 clearance between the upper hole & the wrist pin gives no problems. There is no bushing in the upper end of the rod! The bottom end runs with .015 total side clearance between the crankshaft & what ever induction valve is used. THERE IS NO RUBBING OF THE CONNECTING ROD'S SIDE SURFACES ON THE CRANKSHAFT DISK OR THE INDUCTION VALVE FACE!! Any rubbing in this area causes high friction, heat & wear on the parts involved.
