All text by Tim/Trinc
Katana: changing the oil
this is how i do it, i  will not be responsible for any errors on this page or on your part.
I do not remove the lower cowling.

Warm up the bike and put it on the center stand. place your oil container under the drain bolt & drain the oil. My 13/16 - 6 sided spark plug socket works well in place of the 20mm.

( the oil is hot - don't burn yourself )

Remove the oil filler cover & cap
get yourself an oil filter wrench  the K&N has a 17mm nut so you can use a standard socket.( the K&N is torqued to 18 lb-ft. ) remove the filter & install the new one. there will be directions on the filter for how tight it should be.
Replace & tighten the drain bolt to 16.5 lb-ft.

Add the oil & replace filler cap - start up the bike to fill the oil filter & turn off bike - wait a minute or so for the oil to drain back into the case & refill to the proper lever. ( it must be checked with both wheels on level ground - with the bike upright  - a second person would be handy )

oil change: 3.3 L - 3.5 qt
oil change & filter: 3.5 L - 3.7 qt

Suzuki recommends 10W-40

I will not get into the best oil/filter debate
this time i used a K&N oil filter & Castrol Actevo 10W-40 oil.