Valve Guide: Service and Repair

1. Using suitable tool, machine off protruding valve guides from camshaft side until guides are flush with cylinder head.
2. Place cylinder head on tool 9220 or equivalent.
3. Loosen valve guides from camshaft end with short blows from hammer on tool 9224 or equivalent and press out remainder of guides toward combustion side.
4. Coat valve guides with tallow, insert with light knock and align and press into cylinder head against stop from camshaft side. Press fit for valve guides is .0024-0031 inch (.06-.08 mm). Valve seat inserts must be machined after replacing valve guides. On 1988 928S 4 models, intake valve head diameter is changed from 1.377 inch (35 mm) to 1.456 inch (37 mm). Exhaust valve head diameter is changed from 1.259 inch (32 mm) to 1.338 inch (34 mm). Valve springs and installed distances correspond with those of the 1986 928S. The bearing surface on the cylinder head, however, is machined .078 inch (2 mm) deeper, which is compensated for by the use of .078 inch (2 mm) thicker stepped washers.