Rotax 912-UL Repair Manual page 28

Startingwith engine no.3,792.653, only inlet side is furnished with valve stem seal.
Valve stem seal on the exhaust valve is to be removed. Exchange indurated valve
stem seals.
If the engine 'has been run hot', check in any case hardness of cylinder head material.
Minimum hardness 65 HB.
If need be, the tapped hole for spark
plug can be repaired by utilizing a
"heli-coil" thread insert. Basically this
repair includes reboring of the dam-
aged thread, tapping with a special tap
and fitting of the "heli-coil" insert,
into the newly tapped hole. After fit-
ting the "heli-coil" break off bent end O by turning back, and remove it.
6.6.3) Valve guide:
Check inside diameter and gliding face of valve guide.
Dimension
valve guide intemal dia.
valvc guide cxtcmal dia.
inrcrferencc fit in cylindcr hcad
valvc stem dia.
cleanncc of valve stcm
new mm
(in) wear limit mm (in.)
7,006+ 7,018 (
0,276)
7,15 (0281)
12,O64+ 12,U5 (
0,474) 12,M4(0,475)
0,O16+ 0,075 (0,002 + 0,003)
0,046(0,002)
6,965+ 6,980 (
0,n4)
6,94 (0,273)
0,A26+ 0,053 (0,001+ 0,0O2) 0,15 (0,006)
If wear has reached the specified limits, renew valve guide.
Remove valve spring retainer. Knock off the part of
camshaft chamber O. The guide will break at groove O
and can be pressed out in direction of combustion cham-
ber, using a suitable, stepped punch.
Prior to pressing in a new valve guide coat lower part @
of the guide with slide paste Molykote G-N.
The fitted valve guide is to be reamed to diameter 7,006
+7,018 mm ( 0,276in.). Subsequently
inspectvalve seat,
rework as required and check valve for tightness.
Exchange ofvalve guide on cold en-
gine.
the guide projecting into
I NOTE: