Cylinder head repair (BMW 3 Series E21)

Replacing valve guide bushings

If the valve guides are excessively worn (for wear limits, see subsection "Detailed technical specifications"), replace the valve bushings.

Press out the valve sleeve on a cold engine using tool 111100, pushing the sleeve from the top of the cylinder head towards the combustion chamber.

Check the dimensions of the valve guide bushing seat to the combustion chamber.

Check the dimensions of the valve guide bushing seat in the cylinder head. If the valve guide bushing seat diameter is larger than the permissible value (see subsection "Detailed technical specifications"), bore the seat to the nearest repair size and press in a valve bushing of the corresponding repair size.

Heat the cylinder head uniformly to a temperature no higher than 200°C, lubricate the valve sleeve with grease and press it in with mandrel 111120, acting in the direction from the top of the cylinder head to the combustion chamber, until the mandrel stops against the cylinder head. Using mandrel 111120 ensures proper protrusion of the valve sleeve relative to the plane of the cylinder head, which should be within 15±0.5 mm (see photo).



After the cylinder head has completely cooled, ream the hole in the guide bushing.



Make sure the new guide bushing and valve seat are completely concentric. Resurface the valve seat if necessary.

Replacing valve seats

Replacement of valve seats must be carried out at a service station.

Drill out the valve seat to be replaced; in this case, it is necessary to pay attention to the centering of the drill and avoid removing metal from the valve seat.

Ream the valve seat, maintaining the specified value of the valve seat interference in the cylinder head seat (see subsection "Detailed technical specifications").

Heat the cylinder head uniformly to 200°C and cool the oversize valve seat to minus 70°C by immersing it in liquid nitrogen.

Press the valve seat until it rests against the bottom of the cylinder head socket.

Grind the working chamfer of the valve seat.

Grinding of valve seats and valves

Check the condition of the valve working chamfer. In case of minor damage, it can be ground down, maintaining the proper chamfer angle.

Grind the working chamfers of the valve seats by hand or with a grinding machine.

Grind the valves to the seats and check the tightness of the valves to the seats.

After grinding and lapping the seats and valves, thoroughly wash the seats, valves and cylinder head channels, blow them out with compressed air.

Check the tightness of the valves to the seats by filling the combustion chambers with gasoline, after screwing in the spark plugs.