The internal lubrication system has been installed as standard in all Wärtsilä ZA40S engines manufactured from 1996 onwards. The system consists of a bore-cooled steel crown with combined oil spray and shaker cooling. There are three piston ring grooves and one oil scraper ring on the piston crown. The oil used to lubricate the piston and liner is directly supplied from the oil sump instead of from a dedicated tank. The oil is directly injected between the moving sliding parts, passing through the internal orifices in the connecting rod, piston crown and piston skirt.
Installing an APR increases clearance between the piston top and liner wall and considerably reduces contact between carbon deposits and the liner wall during piston tilting.
The upgrade comprises the following:
- APR-ready piston assembly with internal lubrication system
- APR-ready cylinder liner
- Anti-polishing ring
The upgrade process involves dismantling and reassembling the piston assembly and the cylinder liners and dismantling the external lube-oil circuit. The optimal time to perform the upgrade is during a major engine overhaul, for example at 48,000 hours.