XS6550 USED standard size piston Feb 28, 2014 12:36:06 GMT -5 Quote Select PostDeselect PostLink to PostMemberGive GiftBack to Top Post by Pabeye on Feb 28, 2014 12:36:06 GMT -5 On Ebay open for bids or Buy It Now at $20 one used piston for our favorite bike, the XS, It came out of my 1979 which has about 6500 miles on it. Here is the link:ebay link