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User’s Handbook, TSL 4186E, Issue 2 55
4012/16 Diesel
How to checking valve and seat recession
Special requirements
By the use of tool No. T6253/312, an indication of valve and seat wear (recession) can be obtained without the
removal of a cylinder head.
The tool is to be used as part of the bridge piece and valve clearance setting sequence.
Note: The inlet valves are easily checked but as there is insufficient clearance only one exhaust valve can be
checked.
1 Place the tool on the rocker box face around the bolt (A1). Position the legs of the tool above the inlet valve
spring retainers.
2 The clearance between the legs and valve spring retainers indicates the valve life left. A leg touching a valve
spring retainer indicates the need for a cylinder head overhaul.
3 To check the exhaust valve, place the tool around bolt (A2).
From engine serial number DGK120717U0686F (12 cylinder engines) and DGR161221U0687F (16 cylinder
engines) the following improvements have been introduced:
z The rocker box to cylinder head joint has been improved using a graphite material which is 0,7 mm thicker
than the joint it has replaced.
z Capscrews have replaced the retaining bolts (A1) and (A2).
To check valve seat recession on these engines use a 0,7 mm feeler gauge (A3) in conjunction with the
recession tool (A4).
Special tools
Description Part number Description Part number
Valve seat recession checking tool T6253/312 Feeler gauges UA
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