Over the years, many Valkyrie and Goldwing owners have used diesel oils such as Shell Rotella or Mobil Delvac in their engines. However the new CK-4 diesel standard has caused some controversy. EPA concerns over cat damage have caused many manufacturers to reduce the ZDDP content in their CK-4 oils. ZDDP (zinc & phosphorus) is an important anti-wear additive that benefits motorcycles with integral transmissions. Some new oils reduced it so much that after testing showed increased wear, Ford now recommends the older CJ-4 oils for their diesel engines. So you might want to do a little research on your favorite oil as its composition may have changed.