A cyber friend of mine, Andrew, who happens to also own a Honda CB160 asked if I would be interested in performing a piston modification for his Ducati 160 Monza Jr. He had sent me a document that Tom Bailey wrote outlining changes that could be made to a stock piston for these engines.
The stock 160 piston came with an extra oil ring at the bottom of the skirt. I guess Ducati figured they needed a bit more control. In order to reduce friction and drag some owners opt to cut the bottom oil ring groove off. Once the skirt is trimmed the sides, just below the pin bosses, get a 1.5” radius machined into them in order to lighten the unit up. Once the machining is done the piston then gets polished in order to relieve any stress caused by nicks and scratches.
Since I am not a production machine shop I am not usually set up to perform custom modifications. I am, however, always intrigued by the challenge of figuring out how to accomplish the task. I agreed to give it a go and told Andrew that if I screw it up he’ll be on the hook for a new piston. I guess he figured it was worth the risk because he sent me the piston.
I am happy to say that the minor procedure worked out fine. No money mistakes were made and the piston is on its way back to Andrew.
The following is picture book format of the procedure. It’s nothing too exciting however it involves a piston, metal, and machining so how can that not be cool to look at!
The following is a quick clip showing the milling machine set up for radiusing the piston. The fixture was designed specifically for a 1.5″ radius.