Originally Posted By: kballowe
Originally Posted By: wileyE
Synthetic's can have a lower traction coefficient than the lower groups. Making the additive package even more important to prevent wear.
http://www.valvoline-technology.com/upload/dynamic/Diesel Engine Cam Galling.pdf
Excellent article.
Generally speaking, this is why Harley Davidson would not recommend a full synthetic oil for their engines. Right or wrong, one of the reasons cited was crankshaft roller-bearing "skate".
Of course, the 'other' theory was that Harley did not market a synthetic oil and therefore would not recommend one. Can't make no money off something you're not selling, right?
Still, the article gives some good data. Hopefully, this gets to "those that know" who formulate all the various motor oils that we use.
HD diesel engines really doesn't seem applicable to motorcycle engines, apple/oranges?
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AMSOIL Synthetic Oils: Slipperiness and Wet Clutches
As a side note, we have received many reports of motorcycle shops telling customers that synthetic oil is so slippery that is causes roller bearings not to roll and will result in flat spots on the roller bearings. This is absolutely not true. Synthetic oil is no more “slippery” than petroleum oil. Synthetic oil is more uniform in molecular structure than a petroleum oil but it is not more slippery and will certainly not cause roller bearings to roll. Roller bearings will roll whether they are using petroleum oil or synthetic oil and the only way the roller bearing on the rocker arm will ever stop rolling is if the needle bearings that support the roller bearing failed. Every automotive racing engine (as well as many other types of high performance engines) and most of today’s high performance automobile engines use camshafts with sophisticated roller rockers with absolutely no problems of this nature whatsoever.
We have also received reports of motorcycle shops telling customers that synthetics are so “slippery” as compared to petroleum oils (which simply do not reduce friction as well) that wet clutch packs in their motorcycle transmission and even their automatic transmission of their cars and trucks will slip when using “slippery synthetics” even if there are no friction modifiers present. This is absolutely not true.
Look at it this way. Wet sandpaper removes paint as well as dry sandpaper does. The slipperiness of the water does not impede the sandpaper's ability to function. The same applies to the slipperiness of synthetic lubes in wet clutches. It is simply not an issue. However, just as rinsing the sandpaper keeps it cleaner longer so it functions better longer, so the synthetic lubricant keeps wet clutch plates cleaner longer so they function better. And, since synthetics are superior cooling agents to conventional petroleum lubes, using synthetics will help wet clutches last longer, too.
Petroleum oils have low resistance to heat and allow varnish and glaze to form on clutch plates, which can lead to slippage and increased heat generation and potential failure of the clutch pack. Synthetic oil is going to allow your wet clutches to perform better (especially under extreme heat, RPM and load conditions) and last longer than they would with petroleum oil subjected to the same operational conditions.
As a side note in respect to Automatic Transmission Fluid: synthetic ATF is not more “slippery” than petroleum ATF. The base fluids, whether or not petroleum oil or synthetic oil, play no direct role in the relative friction levels of wet clutches. The friction-modifying additives developed for petroleum oils work just as expected in synthetic PAO’s fluids. The longer the fluid resists oxidation, the longer the original frictional properties remain. The superior oxidative stability demonstrated for synthetic ATF’s thereby leads to extended retention of frictional properties.
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Drew
