Took the head off and noticed a small chunk missing from the rear piston near the powervalves. Cylinder wall is perfect,head is perfect,and the famous pv is secure without damage noted to it.First problem:cant find the piece of piston,could it have blown out the exaust.It is not in the crankcase,or any ports.Second:Even though the pv looked ok I ordered a new Riva PV set for some minor increase in performance,and new piston with rings and all hardware. Will I have to hone the cylinder,if so will a ball style hone be ok,and what size should I use.I have done small engines,and a 302 with this hone,is there anything to keep in mind with the yamaha engine.Third:I have the stage I with d-plate installed.I noticed the text stated to remove the front mounted air box,and internal screen in the carb. air box.Is this safe to do.I would like to get the individual air filters but one thing at an expensive time.All help is appreciated,and any sugestions.Thanx in advance

P.S-Still havent found the reason for piston failure,but did order all new gaskets in case some water snuck in.

Help Please!!!