This is a very stupid and noob question, But me seeing all the available options and what i read from various sources confuse me, Which engine oil is good for K100rs 16v! I once read not to use synthetic oils is it true??

There are many options as you said, but in my experience the best oil is the one that you can easily find, at the lowest cost per mile, and meets the technical criteria indicated by the engine´s maker.
So, for my K´s engine its a mineral 20w50.
For others is a synthetic 10w50.
And you can go on and on.
I think there is not a unique solution.
Best regards
JAP

Any oil that gets changed regularly.  K bike engines are "bulletproof" and short of running them dry will not fail from anything caused by what oil you use.

I've been using synthetic oil in many K bikes for years and years.  No issues.  I usually run Mobil 1 15-50 or Shell Rotella T6 5-40.

Tires are much more important than oil.

No such thing as a stupid question just stupid mistakes from not asking questions.
I use Shel RX5 mineral oil in all my engines even the lawn mower.
For a K bike use any good brand name oil and keep using the same oil. They are robust engines and any good brand name oil nowdays is far better than the best oil available when the bike was made.
I change the filter at each oil change and some at every second change, it's just what you feel comfortable with and in the long run it doesnt seem to matter.

 

Not a stupid question at all, it must be one of the most debatable subjects of all and all sides have their die hards and because of the K car type construction [seperate gearbox and dry clutch] it also includes car and diesel oils, I find regular changes to be the best answer find a good oil you are happy with and change it regular.

BIG D

Silkolene 20w-50 Synth in mine

JR

Thank you all, I finally got Mobil 1 10w-40.

One more question:  when ever i change the engine oil do i have to change the oil in transmission and drives?? can i use the same oil like 10w - 40.???

The transmission and final drive only need the oil changed at every 20 000km or 12 000 miles and use 80w-90SAE gear oil

Looking at your city/state it says SFO. A quick search by me failed to decypher that.

 My point is if you are in a cold climate then 10 W 40 is ok but in a hotter state go for 20 W 50

as recommended by all the above suggestions.

RicK G wrote:No such thing as a stupid question

Just stupid askers.



(Don't take offense. It's just a joke.)

That always make me think of the tradesman I was assigned to when I started my apprenticeship. he would have made 2 of me and I am no midget, he was a New Zealand Maori also a very good tradesman. The first thing he said was " you can ask all the stupid questiond you like but you make any stupis mistakes and I'll kick your arse till your nose bleeds".
That always stuck with me and I have actually said it to a couple of apprentices that I have had working with me.

I used synthetic 20w-50 for awhile, but with my last change I switched to synthetic 10w-40.  I noticed a difference.  Start ups are quite a bit smoother, and the bike seems to be a little happier.  It runs overall smoother and it feels like there's less resistance on the engine.  Like they say, though, anything black and slippery will be just fine.

I use Shell Helix HX5 and have never in 29 years had any failure due to oil but if you ask 200 experts you will get 300 opinions. It has to be the most talked about subject on the planet.
Most of the run of the mill good brand name oils today are far better than the best you could buy when the bricks were designed.
You have a big range but stick with whatever you choose.