Piston: Service and Repair

NOTE: The group number 0, 1 or 2, the piston code number, e.g. 10 and the driving direction arrow are punched into piston crown. The group number is also punched into cylinder crankcase parting surface. Both group numbers (cylinder bore and piston) must be in agreement. The specified piston clearance will then be maintained.

In the event of repairs, hone cylinder bores to dimensions of available piston plus piston clearance.

The piston shank is graphite-treated.

Due to the higher thermic load, the pistons are cooled by means of an annular duct located in piston crowns.


Removal





Attention! To avoid damage to oil spray nozzles caused by contact with connecting rod during removal of piston, remove oil spray nozzles (arrow) first. Service and Repair


Removal





1 Remove connecting rod with piston in upward direction.






2 Remove piston pin lock and force out piston pin.






3 Recondition and square connecting rod. Service and Repair


Installation





4 Place piston on connecting rod in such a manner that the arrow (1) is pointing in driving direction and the lock nuts (2) in connecting rod are pointing to lefthand engine side.

Attention! Do not heat piston.






5 Push-in piston pin coated with engine oil manually.






6 Place piston pin lock into groove.
Check piston rings for easy operation.
Then installing used pistons, check piston rings for gap and side clearance.
7 Lubricate clean cylinder bores, connecting rod bearing journals, connecting rod bearing shells and pistons.






8 Distribute gaps of piston rings uniformly along circumference of piston.
9 Position piston ring clamping strap and insert piston.
The arrow in piston crown should point in driving direction.






10 Place connecting rod bearing cap with code numbers facing each other on connecting rod, lubricate connecting rod nuts, tighten to 40 - 50 Nm preload and 90-100° angle of rotation torque.
11 Rotate crankshaft and check clearance between piston pin eye and connecting rod.
12 In TDC position of pistons, measure distance between piston crown and cylinder crankcase parting surface (refer to specifications).
13 Install oil spray nozzles.