Ever notice how some old wives tales refuse to die? Regardless of how much evidence exists to refute them, many seem to go on forever. One of these canards is the baseless theory that synthetic oil is so “slippery” that it causes cam roller bearings in some Harley-Davidson engines to remain stationary in the bearing race under heavy loads. Allegedly when this occurs, the cam shaft spins on the motionless rollers and scores the surface until a flat spot occurs. Purveyors of this assertion may call it roller bearing “slide”, “slip”, “float” or “skate”.

We had thought that this hogwash was proven false and forgotten years ago. We thought wrong. One of our most faithful customers (who also happens to be a journeyman auto mechanic) told us that he couldn’t use our AMSOIL Synthetic 20W-50 Motorcycle Oil in his Harley for this season. He had been told by the service manager at his Harley dealership to stay away from synthetic oil because it causes roller bearing damage. This was enough to spook our customer back to using conventional Harley Davidson brand motorcycle oil. We were very surprised that this customer was swayed by this groundless warning and wondered if this service manager had just stepped out of a time machine from 1983.

This customer had been using AMSOIL 20W-50 for several seasons and raved about how it eliminated his Harley’s oil consumption, improved his fuel economy, lowered his engine operating temperatures and improved his bike’s throttle response. AMSOIL has been declaring for years that their synthetic oil does not cause roller bearing damage and every season Harley riders log millions of very successful miles using AMSOIL synthetic 20W-50.

To get a technical repudiation of this subject, we turned to AMSOIL Technical Services.

They tell us that roller bearing damage was never due to the synthetic lubricant causing the roller bearings to “slip”. It was due to the bearings being insufficient to handle the loads. At one time Harley-Davidson used cam bearings that had 16 rollers. The 16 roller units would overload and then fatigue. Eventually the roller bearing surface would flake or pit which would cause binding and ultimately flat spotting. Harley-Davidson eventually moved to cam bearings that had 32 rollers which were better equipped to distribute loads.

When this bearing failure occurred, Harley mechanics would often point to synthetic oil as the culprit. Synthetic oils were a new concept to many Harley techs and this new-fangled oil was an easy place to pin the blame. It was easy to tell the customer that the issue was their fault for using some peculiar synthetic motorcycle oil and not Harley-Davidson engine oil. But once Harley-Davidson labelled their own synthetic oil, they had to find other reasons for these failures.

Harley-Davidson corrected their bearing design deficiency long ago, but some still believe this myth.

There are four main reasons for roller bearing failure:

1. Overloading
2. Misalignment
3. Dirt or debris contamination
4. Insufficient lubrication

Oil that is too “slippery” is not a plausible cause. Any flat-earth fears about synthetic oil should have been left in the 1970’s. We have been selling AMSOIL Synthetic 20W-50 Motorcycle Oil since 2001 and without doubt, it is our customers’ most widely acclaimed product. It is simply the most cost-effective upgrade you can make for the performance and protection of your Harley-Davidson motorcycle.

Read more about Synthetic Oil and Harley-Davidson Motorcycles