11.28
Replacing valve guides
•
Heat cylinder head slowly and uniformly to
200 °C (392 °F) in a suitable oven.
e Caution:
Wear protective gloves when handling heated parts.
•
Drive out valve guides with 5 mm (0.20 in) dia. ex-
tractor pin, BMW No. 11 5 674, from the com-
bustion chamber side.
•
Allow cylinder head to cool down to room tem-
perature (app. 20 °C/68 °F).
•
Examine valve guide bore for:
–wear,
– widening taper and
– correct dimensions in H7 tolerance range
(12.500...12.518 mm/0.4921...0.4928 in).
L Note:
Valve guides are installed in the cylinder head with
an interference fit of 0.015...0.044 mm
(0.0006...0.0017 in).
If valve guide bore is undamaged and dimen-
sions are within correct 12.5 H7 tolerance range:
•
Use original 12.5 U6 (12.533...12.544 mm/
0.4934...0.4939 in) valve guide.
•
Measure valve guides with micrometer.
If valve guide bore is undamaged but slightly
larger than the 12.5 H7 tolerance range:
•
Use replacement valve guide
12.550...12.561 mm (0.4941...0.4945 in).
If valve guide bore is damaged or not to correct
dimensions in 12.5 H7 tolerance range:
•
Use an oversize 12.7U6 (12.733...12.744 mm/
0.5013...0.5017 in) valve guide.
Repair method 1 – ream out the bore (if bore is
damaged or not to correct dimensions)
•
Determine actual diameter of valve guide using
micrometer.
•
Open out bore with Ø12.7 H7 mm
(12.700...12.718 mm/0.5000...0.5007 in) ream-
er.
Repair method 2 – lathe-turn the valve guide (bore
must not be damaged)
•
Determine actual diameter of bore with internal
measuring tool.
•
Calculate the nominal diameter of the valve
guide:
Nominal diameter of valve guide = bore dia. + inter-
ference-fit value (0.015...0.044 mm/
0.0006...0.0017 in).
•
Use an oversize 12.7 U6 (12.733...12.744 mm/
0.5013...0.5017 in) valve guide.
•
Turn down oversize valve guide to nominal di-
mension.
•
Slowly heat cylinder head to 200 °C (392 °F) in a
suitable oven.
•
Immerse valve guide in liquid grinding paste.
•
Freeze valve guide with dry ice.
e Caution:
Immediately before pressing in, the temperature
must be –40 °C (–40 °F).
•
Place heated cylinder head flat on workbench or
a similar surface.
•
After cooling, place the valve guide on driving-in
pin, driving-in pin, Ø 5mm (0.20 in),
BMW No. 11 5 673.
•
Insert valve guides into cylinder head with no de-
lay.
•
Allow cylinder head to cool down to room tem-
perature, app. 20 °C (68 °F).
•
Inspect bore in valve guide.
L Note:
Valve guides for repair purposes are produced with
an internal diameter of 5.01 mm (0.1972 in) H7.
In most cases, the bore is within the 5.00 mm
(0.1969 in) H7 tolerance range after pressing in.
If the bore is too narrow, ream it out to size.
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