Inspect the piston rings for the following:
• Abrasive wear.
NOTE: Abrasive wear of the intermediate ring can be indicated by a rapid reduction of the finish coating on the
front face of the ring (A). This is commonly referred to as full face ring wear. This rapid reduction will typically leave
a sharp edge on the bottom of the intermediate ring.
Abrasive wear can also be indicated by concentrated vertical scratches on the top ring (B).
Abrasive wear can be caused by:
• Ingested abrasive material
• Inadequate cleaning during a previous repair
• Particles embedded in the bore
• High soot content in the lubricating oil from extended oil drain intervals
• Scuffing and scoring.
NOTE: Scuffing and scoring is indicated by heavy scratches, metal discoloration, and voids (B).
Scuffing and scoring can be caused by:
• Engine overheating
• Oil dilution
• Improper maintenance of the lubrication system
• Piston cooling nozzle malfunction
• Oil ring plugged by deposits.
NOTE: Scuffing and scoring on the piston rings indicates a breakdown of the oil film on the cylinder bore wall, causing transfer of material from the piston ring face to the cylinder bore.
NOTE: Oil ring plugging is indicated by deposits on the oil ring grooves (B).
Oil ring plugging can be caused by:
• Low engine operating temperatures – long periods of idling or a cooling system malfunction
• Extended oil change intervals
• Use of wrong grade of engine oil
• Use of a poor quality engine oil.
NOTE: Plugging of the oil ring drains restricts oil drain back, which floods the piston ring belt area, resulting in a
loss of oil control.
NOTE: The following measurements are intended for inspecting new piston rings.
NOTE: Before completing this inspection, make sure the cylinder bore is within specification. Refer to Procedure
001-026 in Section 1.
Measure the piston ring gap by installing the piston rings into the cylinder bore in which they will used. Position the
rings below the ring reversal area by positioning each ring in the cylinder 89 mm [3.5 in] below the top deck (A), and
use a piston to square it with the bore.
The piston ring type and location can be identified by piston ring profile.
• Top Piston Ring
• Intermediate Piston Ring
• Oil Control Ring.
Two types of intermediate piston rings are used. The type of piston ring can be identified by the type of coating
applied to the ring.
• The chrome-face intermediate piston ring will have a bare metal appearance.
• The phosphate-coated intermediate piston ring will have a black appearance.
NOTE: The piston ring gap specification for the two types of intermediate piston rings is different.
Use a feeler gauge to measure the gap.
If the piston ring gap is not within specification :
• Verify the correct type and part number piston ring is being used
• Verify the cylinder bore is within specification. Refer to Procedure 001-026 in Section 1.
• Verify the piston ring gap measurement is being taken 89 mm [3.5 in] below the cylinder block deck
• Try another set of piston rings.
After each ring gap is checked and verified, identify the ring sets for installation in the cylinder bore where the end
gap was measured.
