Cylinder Head Bolt Torque and Sequence

420A Engine:

CYLINDER HEAD BOLT INSTALLATION

(1) When installing the cylinder head bolts, check that the shank length of each bolt meets the limit. If the limit is exceeded, replace the bolt.
Limit: Max. 99.4 mm (3.91 in.)
(2) Apply engine oil to the threaded portions of bolts and to the washers.
(3) According to the tightening sequence, tighten the bolts to the specified torque 78 Nm (58 ft.lbs.) using special tool (MB991 654).
(4) Loosen bolts completely.
(5) Retighten the loosened bolts to 20 Nm (14.5 ft.lbs.) in the specified tightening sequence.
(6) Make a paint mark across each bolt head and cylinder head.
(7) Give a 90° turn to the bolts in the specified tightening sequence.
(8) Give another 90° turn to the bolts and make sure that the paint mark on the head of each bolt and that on the cylinder head are on the same straight line.

Caution
1. If the bolt is turned less than 90°, proper fastening performance may not be expected. When tightening the bolt, therefore, be careful to give a sufficient turn to it.
2. If the bolt is overtightened, loosen the bolt completely and then retighten it by repeating the tightening procedure from step (1).