Tanaka TOB-12B 1.2HP outboard motor lower unit gasket

thingiverse

Sometimes you just need a gasket and you can't find the right material / thickness for your needs. In this instance, I needed a replacement fiber gasket that was approximately 1.5mm thick for a really old (well loved) Tanaka 1.2 HP outboard motor's lower unit. These units have been long obsoleted and parts are nearly impossible to find, gasket included. If I had the appropriate material on-hand, it is relatively simple to make a new gasket by putting the sheet material on the housing and using a ball-peen (or similar) hammer to lightly tap the outline, marking and cutting the gasket to the exact shape. The year is 2023 and with the aid of a scanner and some TPU filament, I decided that I would draw up the replacement gasket in CAD and print it! The resulting CAD design was done in FreeCAD using a scan of the lower unit gear case cover (which oddly is still available whereas the packing is not!). The gasket as provided is 1.5mm thick, but as this is a (simple) parametric design, you can readily modify the FreeCAD file (para tab) to your desired thickness. This design has been both bench and field tested and does not leak a drop of oil. The end-of-season tear-down will shed more light and if there was any water infiltration into the oil, it will be plainly evident and I will remove this design. I do not anticipate this eventuality.