30/ENGINE - WORK ON THE INDIVIDUAL PARTS
139
20.12
Cylinder - Nikasil
®
coating
302699-10
Nikasil
®
is a surface protection layer for a coating procedure developed by Mahle. The
name is derived from the two materials used in this procedure - a layer of nickel into
which is embedded the particularly hard silicone carbide.
The most important advantages of the
Nikasil
®
coating are very good heat conductivity,
resulting in much improved performance, low wear, and a lightweight cylinder.
20.13
Checking/measuring the cylinder
302700-10
–
Check the cylinder bearing surface for damage.
» If the cylinder bearing surface is damaged:
–
Change the cylinder and piston.
–
Measure the cylinder diameter at several locations on the
X
‑
and
Y
‑
axes using a
micrometer to identify oval wear.
Guideline
Cylinder - drill hole diameter
Size I
88.000… 88.012 mm (3.46456…
3.46503 in)
Size II
88.012… 88.025 mm (3.46503…
3.46554 in)
Info
The cylinder size
1
is marked on the cylinder collar.
305004-10
–
Using a straightedge and the special tool, check the sealing area of the cylinder
head for distortion.
Feeler gauge (59029041100) (
Cylinder/cylinder head - distortion of
sealing area
≤
0.10 mm (
≤
0.0039 in)
» If the measured value does not meet specifications:
–
Change the cylinder.
20.14
Checking/measuring the piston
0
0
A
A
0
0
A
A
400995-10
–
Use the special tool to measure clearance
A
of the piston rings in the piston ring
groove.
Guideline
Piston ring - groove clearance
≤
0.08 mm (
≤
0.0031 in)
Feeler gauge (59029041100) (
» If play
A
is larger than the specified value:
–
Change the piston and piston rings.
–
Check/measure the cylinder. (
305017-10
–
Check the piston sliding surface for damage.
» If the piston sliding surface is damaged:
–
Replace the piston and, if necessary, the cylinder.
–
Check that the piston rings move easily in the piston ring grooves.
» If the piston ring is stiff:
–
Clean the piston ring groove.
Tip
An old piston ring can be used to clean the piston ring groove.