CYLINDER FINISH
Wossner pistons and rings are engineered for high performance and reliability, using premium materials and manufacturing methods. Cylinder finish and geometry are critical to the operation of the piston and piston ring / cylinder interface. The piston ring does require a break in process to have proper seal in the cylinder bore.
!
NOTE: Always follow your OEM service manual for engine break in, as this is critical to the piston ring seal and ring service life. When in doubt, always check with your dealer or a reputable engine builder for guidelines.
Finishing the cylinder wall with a “plateau finish” is the most desirable finish for the best ring function. In simple terms, a plateau finish is a cylinder wall that can hold lubrication well, while also not having a high RA (roughness average). This is accomplished using several finishing steps for the final bore diameter. It is best to use torque plates when available to minimize distortion. Follow best practices to maintain cylinder roundness / cylindricity / taper. The chart below explains what to expect from each finishing step for best surface finish RA values:
STEP
MATERIAL DISTANCE TO FINISH BORE
EXPECTED RA VALUE
BORE TO ROUGH SIZE
-0.0050” (-0.130mm) -0.0020” (-0.050mm) -0.0005” (-0.013mm)
75-98 30-35 20-25
FINISH STEP 1 FINISH STEP 2 FINAL HONE
ZERO
7-10
FINISH STEP 1 and 2 will create the surface required to retain oil. The FINAL HONE step will remove the high peaks from the initial honing steps – this is the “plateau hone” step. The finishes listed above can be accomplished using known honing stone grit numbers, the chart below illustrates expected RA values from common stone grit size available from Sunnen. Note that cutting pressure can greatly affect the resulting RA value:
STONE / GRIT
SUNNEN CK - CV STONE
CYLINDER MATERIAL
APPROXIMATE RA RESULT
220 220 280 400 600
EHN-512 JHU-525 JHU-623 JHU-818
FERROUS / NICKEL FERROUS / NICKEL
40 – 48 30 – 35 20 – 25 10 – 15
ALUMINUM / FERROUS / NICKEL ALUMINUM / FERROUS / NICKEL ALUMINUM / FERROUS / NICKEL
C30-PHT-731
7 – 10
Source: sunnen.com, goodson.com, cylinderheadsupply.com
!
NOTE: Some aluminum bores require additional honing steps, stone types, and abrasives not listed here
Cylinder cross hatch is important for FINISH STEP 2, as the proper cross hatch angle will provide proper oil retention on the cylinder wall, as well as ring rotation in 4-Cycle engine applications. Cross hatch angles that are too great will shed oil too quickly. Cross hatch angles that are too shallow can cause glazing (not allowing ring seating during break in), as well as slow ring rotation and reduced heat transfer: With proper cylinder finishing you are providing the piston and ring assembly the best opportunity for performance and service CYLINDER DECK SURFACE
335
Made with FlippingBook - Online catalogs