Packard Forum Index » Pre-War (1899-1942)

The comment about not using Packard specifications for piston skirt clearance is correct. Original pistons were auto-thermetic which expanded parallel with the wrist pin. They also were tin plated which allowed for tighter clearances.

Neither cast nor forged pistons do this so they require larger clearances up to .0025 inches. However, in the old days they thought tighter was better which has been cast away via engineering research.

Packard newbie,

From memory, on my OD equipped '41 120 the rear end ratio, 4.36:1, was stamped into the outside edge of the "pumpkin" in about the 7 to 8:00 o'clock region looking to the back of the car. May or may not be the same for your '39. And even if you find it, after scraping off copious amounts of dirt and crud, it may not reflect what's inside the pumpkin if a previous owner has changed the gear set.