K949721 Standard Piston fits David Brown Tractor 770 1290 990One New Aftermarket Replacement Standard Piston for David Brown (Fits Case) Tractors This standard size replacement piston fits the David Brown AD3 49 and AD4 49 diesel engines used in the 770, 990, and 1290 tractor models. It is a piston only part rings are not included. The dish top crown and F3 chamber type are correct for the original engine design. Note: for the David Brown 1290, this piston applies up to serial number 11052360. Specifications