REMOVAL & INSTALLATION
The valve guides are shrunk-fit into the cylinder head. Therefore, this procedure is best left to a qualified automotive machine shop. The procedure is included here for reference purposes.
The valve guides on the M42, M50, S14 and S38 engines typically are not replaced if they are worn, though they can be if necessary. These guides are reamed for an oversized valve stem and a replacement valve used with the appropriately oversized stem.
- Remove the cylinder head.
- Using a suitable valve spring compressor, compress the spring and remove the split keepers. Remove the spring and check it against specifications.
- Check the valve stem-to-valve clearance by holding the valve stem end flush with the end of the valve guide and rocking it sideways.
- If the clearance is excessive, the guide must be driven out (into the combustion chamber) with a drift of the proper diameter and replaced.
- To install new valve guide, the cylinder head must be heated to so the new guide can be pressed in without excessive pressure. The guide is then pressed in. Bmw special tool 11 1 20 (or the like), incorporates a recess which provides the proper protrusion.
STEM TO GUIDE CLEARANCE CHECKING
See Figure 1
- The head should be disassembled so the valve can be moved by hand. Remove the valve spring.
- Clean the valve guide and the valve stem. Lightly lubricate the valve stem and insert it into the valve guide.
- Install a dial indicator with the push rod parallel with the cylinder head deck.
- Place the end of the valve stem flush with the end of the valve guide on the cam side of the head.
- Place the tip of the dial indicator on the edge of the valve and measure the distance the valve can move back and forth. This is the guide rocking measurement as bmw calls it or the stem to guide clearance as it is called.
- If the measurement is greater than recommended, have the valve guides replaced and reamed for the existing valves or have the guides reamed oversized to match new valves with oversized valve stems. The valve guides on the M42, M50, S14 and S38 engines typically are not replaced if they are worn, though they can be if necessary. These guides are reamed for an oversized valve stem and a replacement valve used with the appropriately oversized stem.