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42 – English
• Measure piston ring wear. This should not
exceed 1 mm. Use the piston to push down the
piston ring.
• The needle roller bearing is undamaged.
• The inlet manifold is undamaged.
• Pressure test the decompression valve.
• Also refer to Jonsered’s Analysis guide for piston
failures, art. no. 108 07 01-01.
Decompression valve – pressure
testing
1
Connect tool 502 50 38-01 to the decompression
valve.
2
Pump up the pressure to 80 kPa (0.8 bar).
3
Wait 30 seconds.
4
The pressure should not be less than 60 kPa
(0.6 bar).
Repair instructions
8
When replacing the cylinder 340, 345:
Unscrew the decompression valve. (345)
Remove the intake system, see “Air intake system
– removal”.
Model 350 is fitted with a spacer, which is secured
using four bolts from the underside. The spacer
does not however need to be removed when
removing the cylinder.
Cleaning and inspection
Clean all the components, scraping off all traces of
old gasket and carbon from the following places:
• Piston crown
• Top of the cylinder bore
• Cylinder exhaust port
• Decompression valve channel (340, 346XP,
350, 351, 353)
• Cylinder base and/or crankcase
Check the following:
• The surface coating of the cylinder is not worn
through, especially in the upper part of the
cylinder.
• The cylinder is free from score marks and areas
of wear.
• The piston is free from score marks. Small
scratches can be polished out with fine emery
paper.
• The piston ring is not burnt into its groove.