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old_kaw wrote: Also zed1015 posted something about synthetic oil's molecular structure was not right for roller type rod bearings a while back in KzR too. I don't remember the specifics of zed's post. Perhaps he can chime in.

The only fully synth I use is Rock oil TRM20/60 which is specifically formulated with larger long chain molecules for roller cranks / big twins , Harleys etc .
I use that in the drag bike and the Drouin Supercharged from first build with no issues.
Everything else gets any old 20/40 semi which is more than good enough for these motors.
I have noticed that if you change to fully synth from semi on an oil change there is a tendancey for the bike to smoke and an increase in oil weepage from areas that were previously oil tight and changing back to semi cures it.
I have had quite a few customers putting in expensive fully synth because they think it must be better only to get oil leaks and a smoke trail like the Red Arrows Air Display

cb900f wrote: I run synthetic in a bunch of old and new cars, trucks and bikes and have never had a leak.

I used to own a CB900F Super Sport with the 1000cc big bore kit.




Keep in mind that only in the past 15-20 years have auto makers (GM) / petroleum industries (or the general population for that matter) have just recently figured out what chemical structures do not attack the plastic and rubber compounds in the new composite gaskets (composite plastic / rubber GM intake manifolds) and seals used specifically in the GM vortec intake manifolds by using dex-cool, over silica based "green" coolants. I was referencing a college class based upon technology from the late 70's when leakers were the norm..

that said..

With the widespread use of synthetics, rubber chemical compounds have evolved to a happy medium of withstanding almost any lubricant on the market.

For those (such as myself) this is a Red Arrows air display.

That 81 'Halloween' colour scheme was the best of all the 900's IMHO (mine is a beautiful silver 82 but I do think that black and Orange 81 looks best)