LONCIN G250F User Manual

Section 4 Disassembly and service
Stem –to- guide clearance
Subtract each valve stem OD from the corresponding
guide ID to obtain the guide-to-stem clearance.
Standard
Service limit
IN
0.02-0.044 mm
0.10 mm
EX
0.06-0.084 mm
0.12 mm
If the stem-to-guide clearance exceeds the service
limit, determine if the new guide with standard
dimensions would bring the clearance within tolerance. If
so, replace the guide (or cylinder head ) as necessary and ream to fit. If the stem-to-guide
clearance exceeds the service limit with new guides, replace the valves as well.
Recondition the valve seat whenever the valve guide is replaced.
Cylinder head service
Exhaust valve guide replacement
The intake valve guide is not replaceable. If the
intake valve guide is worn beyond the service
limit,
Replace the cylinder head.
1. chill the replacement exhaust valve guide in
the freezer section of a refrigerator for about an
hour.
2. use a hot plate or oven to heat the cylinder
head evenly to 150℃(330℉)
Check the temperature with a temperature
indicating stick (available at welding supply
stores) or equivalent.
Wear heavy gloves to prevent burns when
handling heated cylinder head.
Notice
Do not use a torch to heat the cylinder head;
warpage of the cylinder head may result
Do not get the head hotter than 150℃(330℉);
excessive heat may loosen the valve seats.
3. remove the heated cylinder head from the hot
plate and support it with wooden blocks. Drive
the exhaust valve guide out of the head from the
combustion chamber side.
Notice
When driving the valve guide out, be careful not to
damage the head.
4. remove the new exhaust valve guide from the refrigerator.
4-21

LONCIN G250F Specifications

General

Brand	LONCIN
Model	G250F
Category	Engine
Language	English