Modern oils are far better than what used to be available, and those improvements (along with improvements in engine materials) are making it routine for engines to last longer than the rest of the car or motorcycle.....it is not unusual for an engine to be running long after the rest of the chassis has been worn out.  When I was in my teens any car with 100,000 miles was worn out - now 200,000 is pretty common, and more than 300,000 miles can be achieved with the original engine.

Our Suzuki Savage engine has a bottom end with ball and roller bearings for the rod, crankshaft and transmission - and the bottom end is really flexible about the type of oil that is used.....and the piston/cylinder is also a bit insensitive about the type of oil.  However - the cam and rocker assembly in the Savage is very sensitive to the type of oil you use - it is important to stay within the recommended viscosity to that the cam and rockers get adequate oil flow, and that you use an oil with an adequate amount of ZDDP to keep the cam lobes and rocker arms protected (the old gray hair members of this forum have come to believe that somewhere between 1,000 - 1,200 ppm of ZDDP is needed fore engine longevity).

The attached YouTube video is very good at dispelling a lot of the myths about Synthetic oils and why it is fine to use them in vintage engines.  It also explains why supplementing the oil with oil thickeners (STP, Lucas) is not necessary or desirable in an engine (but it can be useful in transmissions).  Unfortunately this video does not discuss the ZDDP issue and why older engines can suffer cam and rocker wear when a modern engine oil is used in a vintage engine - but the video is definitely worth watching.

https://www.youtube.com/watch?v=pPFSR-2lhxY

10w30 used to be the standard for everything when I started to drive, 60 years ago!
Now, my 2012 Civic coupe uses 0w20 and it's only available in Synth! It's like frickin' water!
When did all this happen????
Cheers!

Thanks for the vid Dave.  I didn't know rotaries injected oil into the combustion chamber.

I talked about oil to one of my Harley friends, he has three different oils, we got one, for everything!
I think that our engin is kind of modern, but Harleys three different casing, engin, gearbox and transmition.. newer Harleys cant be that old in specification that couldnt use the same oil?
In any case, we got an aircold engine, a overhead camshaft, a camshaft chain, a wet coupling.. its probably enginerd to go for a singel oil?

Its probably the cam and the chain that put moste of the strain of the oil, and mayby the cylinder/piston and the clutch that put some dirt in the oil?

If its, change oil frekvently, every year or at last every second year?

And to the topic of viscosity, modern oils is often better to keep the viscosity in all kind of temperture.

To that, modern oils are better at not breaking down att higer temperaraturs.

In any case, our engin is a 80s enginerd and then they didnt have all those modern oils, it probably could go whit those oils but mayby some more oil changes!

To that.. I have not read the manual that much.. but I have read several other manuals, for cars and bikes.. its often says, if one live in a very hot region, one can use a higer visciosity oil.. its common sens?

And to STP and other aditives,
whereby  I only use it on worn out motors, to get my a extra year befor I anyhove need to buy a new car.
But cars have dry clutches, our engin has a wet clutch, I dont think one like to have a very slipper clutch?

I have been wanting to update the oil thread.......we don't recommend using the ZDDP additive anymore, as we have learned that Rotella has enought ZDDP.  There was also a short period of time when T6 in the white bottle had too much moly and was causing clutches to slip.

The recommended oil is either Rotella T6 in 5W-40 (the 15w-40 can also be used if you don't ride in cold weather) - or the T4 in the 15W-40.

The "W" rating is measured at 0 degrees C (32f) - most of us never ride at those temperatures......the T6 rating of 5W would likely be a better oil if you ride in cold temperatures.