Usage:
325 (7TG, 8JG, 9SG, 8NL, 6RM),
325 L (7CJ, 7LJ, 2JK, 6KK, 8NK, 2SL, 9KL, 7LM),
325 N (2SK),
325 LN (3LL) Excavators;
613C (8LJ) Wheel-Tractor Scrapers;
950F (7ZF, 6YG, 4DJ, 5SK) Wheel Loaders;
D20D (9MG),
D250D (6NG) Articulated Trucks Powered By 3116 Machine Engines With Two Piece Pistons
Since the introduction of the 3116 engine there have been several changes made to the two piece pistons used in some applications. Two former piston crowns and skirts have been canceled, and replaced by several new crowns and a new skirt. The correct new piston crown and skirt to use when replacing one of the former crowns or skirts depends upon the engine application. Consult the chart to determine the correct new piston. The new skirt must be used with all of the new piston crowns, and should not be used with the former piston crowns. The former skirt should be used only with the former piston crowns, and should not be used with any of the new crowns listed.
NOTE: Some 3116 engines use 1-piece aluminum pistons, and are not discussed here.
Piston crowns differ due to features such as compression ratio, tight top land compared to loose top land, size and shape of the bowl (crater), height or position of the rings, type of ring, etc. The former piston crowns had a top ring position 5.0 mm (.20 in) from the top of the piston. The later piston crowns have the top ring position 9.5 mm (.37 in) from the top of the piston. Other features are not readily visible. Always use the Parts Manual to determine the correct parts. This chart is intended to help in the selection of the correct new piston crown and skirt, when replacing one of the former piston crowns or skirts which have been canceled.
When replacing former crowns/skirts with new crowns/skirts listed, Caterpillar suggests that all cylinders of the engine be equipped with the new crowns/skirts. Mixing of former and new crowns/skirts in the engine could result in slight engine vibration or a slight difference in the way the engine sounds.
NOTE: There are other piston crowns available which have other differences in crater design, ring grooves, etc. This article is only intended to show the recommended replacement crowns for 7E-3226 and 6I-1512 Crowns, based upon the application of the engine.