Measuring The Piston/Cylinder Mounting Clearance; Checking The Piston Ring End Gap - Husqvarna FC 250 2015 Repair Manual

17 ENGINE
17.4.16

Measuring the piston/cylinder mounting clearance

17.4.17

Checking the piston ring end gap

-
Check the piston rings for damage.
If the piston ring is damaged:
-
Change the piston ring.
•
I
-
Check the piston pins for discoloration or signs of wear.
If the piston pin shows severe discoloration/signs of wear:
-
Change the piston pin.
-
Place the piston pin in the connecting rod and check the seating for play.
If the piston pin seating has excessive play:
-
Change the connecting rod and piston pin.
-
Measure the piston at the piston skirt, at right angles to the piston pin, at a
C,.
distance
Guideline
C,
Distance
Piston - diameter
Size I
Size II
• Info
I
Piston dimensions
-
Check/measure the cylinder.
-
Check/measure the piston.
-
The smallest piston/cylinder mounting clearance equals the smallest cylinder bore
diameter minus the largest piston diameter. The largest piston/cylinder mount­
ing clearance equals the largest cylinder bore diameter minus the smallest piston
diameter.
Guideline
Piston/cylinder - mounting clearance
Size I
306757-10
Size II
Wear limit
-
Remove the piston ring from the piston.
-
Place the piston ring in the cylinder and align with the piston.
I Guideline
Below the upper edge of the cylinder
-
Measure end gap
Guideline
Piston ring - end gap
Compression ring
306113-10
Oil scraper ring
If the end gap is greater than the specified measurement:
-
Check/measure the cylinder.
Info
Mount the piston ring with the marking facing upward.
27 mm (1.06 in)
77.955 ... 77.965 mm (3.06909 ...
3.06948 in)
77.965 ... 77.975 mm (3.06948 ...
3.06988 in)
O
are marked on the piston head.
(� p. 148)
(� p. 148)
0.035 ... 0.057 mm (0.00138 ...
0.00224 in)
0.037 ... 0.060 mm (0.00146 ...
0.00236 in)
0.070 mm (0.00276 in)
1
20 mm (0.79 in)
9
with a feeler gauge.
I
:5 0.40 mm (:5 0.0157 in)
I
:5 0. 70 mm (:5 0.0276 in)
(ll,ll p. 148)
149