Oil weight for KZ550 LTD

Hello all, I have read up on a LOT of posts concerning oil, and I'm aware of the additives and the oil certifications that I have to look for. What i'm deciding on now is weight for my 1981 KZ 550 . I use my bike ONLY in the summer, however my daily weather fluctuates a lot. Since i work in a harbour, we either have very warm/hot weather (25-30 celsius), or pretty chilly weather in the morning, around 15 celsius. However, it never really goes below that in the summer. I ride only about 10 minutes to work but i leave at around 7am when its chilly, and come back at around any time from mid day, to 9pm depending on the day. I am looking for a weight that would work for those temperatures. I'm currently running a 20w-50, but it's a really bad car oil (not JASO-MA) that the previous owner put in, and I want to switch it out before the season really kicks in. Any and all suggestions are appreciated!

10W40 for sure. With these plain-bearing cranks, 20W50 really drags the motor. It ends up running hotter and slower.

Something with roller mains might like the 20W50.

thank you! i've only had old two strokes till now so i'm just making sure i get it all right!

ellipsesKZ wrote: .........we either have very warm/hot weather (25-30 celsius), or pretty chilly weather in the morning, around 15 celsius..................)

30 degrees Celsius is a mere 86 degrees Fahrenheit - believe me, that is NOT a hot temperature at all and 15 degrees Celsius (59 degrees Fahrenheit) is not cold at all! As loudhvx recommended, use 10w40 motor oil and make sure it is labeled JASO-MA compliant. Ed

thank you ed! I purchased 10w-40 based on both of your replies (well to be honest i did after loud replied, but ill include you to reaffirm my decision ).

Shell Rotella is great oil for bikes. Cheap and commonly available.

Does Rotella T4 or T5 work, too but just not as well as T6??
So Rotella 10W-40 works well w/ wet clutch? Much appreciated thank you

All of them work just fine.
T4 is non-synthetic
T5 is a synthetic / non-synthetic blend.
T6 is fully synthetic

Thank you! How about viscosity for an 82 GPZ1100 ....10W-40? 15W-40? 20W-50? Thanks in advance!

I would choose 10W-40.

TexasKZ wrote: I would choose 10W-40.

Can't go wrong with 10W-40.

The W stands for winter, and references a cold temperature viscosity (or the ability to flow when cold.) A lot of engine wear occurs on cold start up and using an oil with a low W rating is good. The lower the better actually.

The second number, 40 or 50 typically, is a hot temperature viscosity rating. The bearing clearances are designed around this number so don't go below 40 or above 50 without damn good reason. Roller bearing cranks don't care all that much about the oil thickness but plain bearing engines like the 550 do. Oil starvation in the 550's is not unheard of so don't go too thick.

Sorry ellipsesKZ Didn't mean to mob your post LOL The reason I chimed in is because I'd already purchased Rotella T6 15W-40 (Walmart wasn't stocked with any 10W-40 T6. An old friend told me it'd be alright during the blazing hot summer, BUT I know that ya'all know yer stuff more than he does.

If you guys think I shouldn't use 15W-40 then by all means, please let me know. Thank you.