Are oils rated higher than 'SG' bad for roller bearings?

[KEITH KRAUSE]

I brought this up at another topic but I would like to hear more ideas. Some of you may remember about 4 years ago, there was a section at this site that talked about oil. Some of that info is still there,(good reading-garage section)but the part about oil 'rating' is gone. I was going to ask Frank why but I know he's busy moving. The article was fairly technical but easy to understand and very believable. To make a long story short, it said that oil with an API rating higher than 'SG' was actually too slippery for roller bearing cranks, which a lot of us have. It said the bearings would actually have a tendency to slip or slide, instead of roll. Since reading that article,I have religiously put only 'SG' rated oil in my motor. You can still find it at bike shops(a couple of brands), but I don't see it at auto stores.If the 'SG' is inferior in lubrication qualities,then why is it still produced? It must be made with something specific in mind? I use Motul 3000 10/40 in my motor since my rebuild and after 12,000 miles I have no complaints. If they do ever stop making it,I guess I'll have to go with the higher rated oils. Do any of you have info or ideas about this?

[Anonymous]

Doesn't sound likely to me. The reduction in friction to allow a roller to slip in that way would need to be huge. Newer oils may or may not reduce friction a little, but there's no way they could reduce friction that much.

Ball and roller bearings are used in gazillions of applications with all kinds of lubricants, and they don't have any problems like that anywhere else.

If you think about the way a roller bearing is loaded, there is almost no tendency to push the rollers in that way. In any case if the bearing did have so little friction as to slip as suggested, would it matter? i doubt it, as many plain bearings work in this way anyway.

As has been said many times before in oil related threads, there's never been a case of engine wear caused by oil brand or type in a GS, only wear caused by inadequate maintenance (oil changes).

One last but important point: remember that there are plain bearing in your engine too; the cams. These would surely benefit from the best oil you can get. You're much more likely to get ruined cam bearings than a crank.

There's so much contradictory information around about oil, yet at the end of the day, which oil you use doesn't really seem to matter!

Just my tuppence worth.

[AOD]

Keith, the rating system for oils is to distinguish which ones are better lubricants, heat exchangers, cleansers, and corrosion inhibitors. oil does all four of those things, not just lubricate like most people think. if an oil is given a higher rating then another oil, its plainly a better oil. meaning if you used it in any engine you should see better results in the long run.

~Adam

[Anonymous]

.... meaning if you used it in any engine you should see better results in the long run.

~Adam

Adam, can you tell me what better results I should see?

[redliner1973]

The main difference in SG vs SL oils if the reduction in Zinc phosphate ( a wonderful anti-scuff additive, but harmful to Cat converters) and an increase in Moly to counteract the Zinc reduction. Newwer oils are no more 'slipperier' than SG-rated. Another SL-advantage is the improvement in VI improvers, meaning the oil will keep it's origianl viscosity better now than when SG oils were made in the late 80's. However, SG rated oils made nowadays have the improved VI's and the origial anount of Zinc Phosphate in them This is the reason you only see it in 'motorcycle oils'. But just remember this, Zinc Phosphate is a wonderful anti-scuff agent used when an oil breaks down enough to inadequately lube a bearing, it relies on the zinc to prevent the metal to metal scuffing that would otherwise occur. But if your oil is already that far gone..... Nowadays alot of oil manufactures use a type of moly to replace this zinc. Alot of this is where you hear people complain about clutch slippage. moly is a very good lube, as to whether it actually makes a clutch slip? i donm't know. I regularly use Castrol 20w-50 4-stroke motorcycle oil (it is rated 'SG' ) but when it is not available I use regual castrol and have had absolutely no problems with it. Just stay away from all 'Energy conserving' oils. these are identified with a 'starburst' symbol on them, but are usually reserved for lighter weight oils such a s 10w-30 and such, however someone lately has reported Pennzoil's 10w-40 is no rated Energy conserving. Check the bottle. Hope this helps.. :twisted: