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. An example is the baseless theory that synthetic oil is too “slippery” for Harley-Davidson cam roller bearings. The suggestion is that the bearings remain stationary once they are bathed in synthetic oil and put under heavy loads. Allegedly when this occurs, the cam shaft spins on the motionless rollers and scores the surface until a flat spot occurs. The assertion is that the roller bearings “slide”, “slip”, “float” or “skate”.
We had thought that this theory 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 V-Twin Synthetic 20W-50 Motorcycle Oil in his Harley 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 Harley-Davidson-branded mineral oil. We were very surprised that this customer was swayed by this groundless warning.
This customer had been using AMSOIL V-Twin 20W-50 for several seasons. He had previously raved about the product. It had eliminated his engine’s oil consumption, boosted his fuel economy, lowered his engine operating temperatures and improved his bike’s throttle response.
AMSOIL guarantees that their synthetic oil does not cause roller bearing damage. Every season, Harley-Davidson owners log millions of very successful miles using AMSOIL V-Twin Synthetic 20W-50.
The Real Reason Some Harley-Davidson Roller Bearings Failed
AMSOIL Technical Services tells us that roller bearing damage was never due to synthetic oil causing the roller bearings to “skate”. The real reason is that some older Harley bearing configurations could not handle heavy loads. At one time, Harley-Davidson used cam bearings that had 16-rollers. The 16-roller units would overload and then fatigue. Ultimately, the roller bearing surface would flake or pit which would cause binding and ultimately a flat spot. Harley-Davidson eventually moved to cam bearings that had 32-rollers. The 32-roller design was 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. This was an was an easy place to pin the blame. It was easier to tell the customer that the issue was their fault for using some peculiar synthetic motorcycle oil. But once Harley-Davidson introduced their own synthetic oil, they had to find other reasons for these failures.
Harley-Davidson corrected their bearing design deficiency long ago. But this myth is still floating around.
Reasons For Roller Bearing Failure
There are four main reasons for roller bearing failure:
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 and roller bearing should have been left in the 1970’s.
To conclude, AMSOIL V-Twin Synthetic 20W-50 Motorcycle Oil is the most cost-effective (and safe) upgrade you can make for your Harley-Davidson motorcycle.