KS Kolbenschmidt pistons with keystone-shaped connecting rod recess
Improved lubrication and cooling
Why do some pistons have unusual connecting rod recesses? This is a conscious improvement and not a construction or design error. Pistons with keystone shaped connecting rod recesses are increasingly being used, even in pistons with straight connecting rods. The benefits include improved lubrication and cooling of the piston pin bearing and there is therefore higher stress resistance.
This is not – as is often suspected – due to the shape or piston being incorrect, but is actually an intentional optimisation.
- A larger gap between the connecting rod and piston pin boss. This allows more splash oil and centrifugal oil to get to the piston pin from the crankshaft and the cooling oil nozzle.
- The greater application of oil leads to improved cooling and lubrication of the piston pin bearing at high stresses.
- The piston pin has more free space in the direction of the crankshaft (on the pressure-relieved side) to allow it to be elastically deformed.