11.30
Replacing valve guides
e Attention:
Wear protective gloves when handling heated parts.
•
Heat cylinder head slowly and uniformly to
200 °C (392 °F) in a suitable oven.
•
Drive out valve guides with 5 mm (0.1969 in) dia.
drift, BMW No. 11 5 674, from the combustion
chamber side.
•
Allow cylinder head to cool down to room tem-
perature (approx. 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 press-fitted 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 but slightly lar-
ger 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 12.7 u6
(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.
•
Ream bore with Ø12.7 mm (0.5000 in) H7
(12.700...12.718 mm/0.5000...0.5007 in) reamer.
Repair method 2 – turn the valve guide on a lathe
(bore must be undamaged)
•
Use bore gauge to check internal diameter of
valve guide.
•
Calculate the nominal diameter of the valve
guide:
Required 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.
•
Machine oversize valve guide to required diameter.
•
Slowly heat cylinder head to 200 °C (392 °F) in a
suitable oven.
•
Immerse valve guide in liquid grinding paste.
•
Chill valve guide with dry ice.
e Attention:
The temperature must be –40 °C (–40 °F) immediate-
ly prior to insertion.
•
Place heated cylinder head flat on workbench or
a similar surface.
•
Mount the chilled valve guide on
dia. 5 mm (0.1969 in) drift, BMW No. 11 5 673.
•
Drive valve guides into cylinder head with no de-
lay.
•
Allow cylinder head to cool down to room tem-
perature, approx. 20 °C (68 °F).
•
Inspect bores of valve guides.
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 press-
ing in.
If the bore is too narrow, ream it out to size.
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