Service Manual

ENGINE TOP END 5-15
Cylinder, Piston
Piston Cleaning
•
Remove the piston and piston rings (see Piston Removal).
CAUTION
Never clean the piston head with the engine assembled.
Carbon particles will fall between the piston and cylinder, and
damage the crankshaft bearings.
•
Scrape the carbon off [A] the piston head.
•
Use the scraping tools carefully. Do not gouge the piston head. To
avoid gouging, use scrapers that are made of a material that will not
cause damage.
•
Clean the piston ring grooves [A] with a broken piston ring or other
suitable tools.
CAUTION
Be careful not to widen the ring grooves. Damaged ring
grooves will require piston replacement.
Piston Ring and Ring Groove Wear
•
Clean the piston (see Piston Cleaning).
•
Visually inspect the piston rings and ring grooves.
If the piston rings are worn unevenly or damaged, replace them.
If the ring grooves are worn unevenly or damaged, replace both the
piston and piston rings.
•
Check ring grooves for wear by inserting a new ring in the proper
groove at several points around the piston.
•
Measure the clearance between the top and second rings and their
grooves using a thickness gauge [A].
If the piston ring/groove clearance is greater than the specified value,
replace the piston.
Piston Ring/Groove Clearance
Service Limit
Top 0.18 mm (0.007 in.)
Second 0.18 mm (0.007 in.)
NOTE

The oil ring is a three piece assembled ring. It is difficult to measure
the ring groove clearance and thickness, visually inspect only.
•
Measure the piston ring thickness [A].

Use a micrometer to measure at several points around the rings.
If any of the measurement are less than the service limit, replace the
entire set of rings.
Piston Ring Thickness
Service Limit
Top, Second 1.40 mm (0.055 in.)
NOTE

When using new rings in a used piston, check for uneven groove
wear. The rings should fit perfectly parallel to the groove sides. If
not, replace the piston.