I am in the process of gathering information and the necessary parts to overhaul/reassemble my O-235 C2C engine for my 601 XLB. I've hit a bit of a quagmire with the pistons I have on hand (and the parts number changes over the years). I have 3 used pistons that are in very good shape with the part number 61147. The 4th unit I have on hand is brand new with a part number of 73851. According to the overhaul manual both parts are interchangeable, but there is a 42 gram difference in weight as the newer one much lighter. It would not be good to assemble and run an engine with such a large weight discrepancy. Lycoming says no more than a 20 grams between each piston assembly. The other three pistons are within 2-3 grams as are the rods. Now there is another superseding part number for the piston (can't remember it off the top of my head 14B23919 I think), and they are $expensive$ and thats if you can find any. Does anyone have any ideas know a good source for used lycoming parts?  

I will be sending out the crankshaft and cam for inspection and reconditioning. Cylinders are ready to go. Carb is overhauled. Valve train is good to go. I'm making progress but this piston issue is kicking my butt. 

I know better than do rebuild a C series engine now. 

Thanks in advance. 

Mike