Set of 4 OEM VW pistons for 1.9 liter TDI, Oversize, includes Pins and rings .5mm over stock
part numbers
038107081AA Cylinder 1&2
038107081AB Cylinder 3&4
Manufactured by Nural/Federal Mogul, the company that supplies the replacement pistons for VW dealerships.
Note: When replacing the engine block, rods, crankshaft, and especially pistons it is imperative to measure piston protrusion at TDC above the block deck in order to select the correct head gasket thickness. Projection MUST fall between .91mm and 1.20mm & have the appropriate head gasket thickness to achieve the correct compression ratio.
Piston to wall clearance is not a dimension specified by VW. I have attached the bore and ring specifications from the factory repair manual. LINK TO PISTON DIMENSION DOCUMENT
Also please note the importance of piston projection above the block. This is critical for maintaining correct compression ratio and orientation of the air charge in the piston bowl. Essentially VW is looking for 1mm of projection above the deck. The different head gasket thicknesses compensate for deviation here. Failure to achieve the correct projection dimension will result in reduced torque, power, and excessive smoke. LINK TO PISTON PROJECTION DOCUMENT.
Many (but not all) oversize pistons are under-height to allow for deck milling. I recommend confirming this by comparing the measurement between the top of the wrist pin bore and the piston crown for the new VS original pistons. The difference is probably .25mm.
If the new pistons are under height the most sure way to hit the target projection dimension is as follows: Bore the block, assemble the rotating assembly & pistons, measure piston protrusion, disassemble, and mill the deck accordingly. Obviously that is labor intensive. Another approach with slightly more risk is to mill the deck by the under height dimension calculated by comparing pistons. Assuming an in-spec deck with the original pistons, this would result in an in-spec deck post machine work.
Note that milling the head does not affect piston projection & head gasket selection. Rather if the head is milled the valve seats must be cut the same depth to maintain correct geometry. If the seats are not cut deeper valve projection may become excessive & piston to valve contact may occur. Do not compensate for incorrect valve projection by installing an excessively thick head gasket...this will lead to compression ratio problems.
Main bearings - All upper and the #3 lower journal gets a grooved bearing shell.
https://kermatdi.com/files/1-9-piston-and-connecting-rod-overview.pdf
https://kermatdi.com/files/1-9-piston-dimensions.pdf
https://kermatdi.com/files/piston-projection.pdf
