My dad says that the prong of a piston circlip must be aimed at the bottom of the wrist pin groove. He says if the circlip isn't aimed downward it can jump out of the groove when revving the motorcycle. True?

Sorry to say your dad has it wrong.. While most tuners do put the open end of the circlip at the bottom, it makes no difference.

What is important is how you put the crclip into the piston. The best way is to grab the circlip's prong end with needle nose pliers and slightly angle the clip into the groove and gently force the other end into the groove. Use a small screwdriver to verify that the clip is fully seated in the groove.

Do not grab both prong ends at the same time and squeeze the clip together or the clip will lose its spring tension.

When rebuilding an engine there are a multitude of small parts that undefined must be installed correctly. The simplest of a motors complex parts list is the spring wire circlip. Installed correctly, in the piston pins groove, it never causes a problem. But, if incorrectly installed, severe cylinder damage can result.

The proper way to install a circlip is to position one end of the clip in the groove with the other end at 30deg. past the cut out. Now, using a very narrow flatblade screwdriver, lever the clip undefined inward and into its groove. You will hear it snap into place if done correctly.

Note: just in case you slip, cover the area under the piston's skirt with a rag to prevent the clip from falling down inside the engine.