If the valve adjusting screws have reached their end and there is still insufficient valve clearance, the cause may be (a combination of):
- the valves sit too deep in the valve seats
- the cylinder head sleeves have sunk deeper into the cylinder head over time.
In our experience, the sleeves at the exhaust side sit usually deeper than at the intake side.
Below an example of 2 R27 cylinder heads.
The RHS sleeve at the intake side of cylinder head 1 has a height of 88.47 mm
The LHS sleeve at the exhaust side of cylinder head 2 has a height of 87.51 mm, almost 1 mm lower
The top view of cylinder head 2 shows how much height difference there is between the 4 sleeves.
The difference between the lowest and highest sleeve is 0.49 mm.
It pays to fit shims between the sleeves and the rocker arm support brackets: to compensate for the loss of height and to level the adjacent brackets so that the rocker arms are as close as possible at a 90 degree angle to the valve stems.
Shims can be found here: 11330034110
