Yeah, I know, “what oil should I use” is what bored or clueless folk post on any FaceBook motorcycle forum to see how many pointless comments they can get. Everyone has an opinion on what oil should be used, which is generally what they use, backed by nothing more authoritative than “I’ve been using this for XX years” . Here’s the thing–doing the same thing for a long time is more an indication that the poster has never considered or studied alternatives. It’s more a borderline admission of stubborn stupidity rather than a qualification.
I love to learn new things, I don’t consider long experience to be a qualification. As I’ve said many times, I’ve been working on bikes longer than most of you have been alive, and I do stupid shit every day. But I do look for expert information, so I’m pleased to offer this email I recently got from “Toxic Terry” who I’ve received great information from previously about chain lube. This is sort of a continuation of that discussion and I hope to take this a bit further this spring, with a deep dive into general lubrication issues, as goofy as that sounds when I type it. Anyway, here’s the latest from Toxic Terry:
I am the fellow rider who sent you information concerning the potential use of DigiLube Ultra Film 1 for motorcycle chain maintenance. As a retired organic chemist, my interest in lubricants has grown exponentially over the past years as the evolution of synthetic lubricants has become a reality. In the case of DigiLube, the base oil is conventional, but the additive package is synthetic in that the specific lubricant to provide ‘dry lubrication properties’ is a compound that effectively bonds lubricant molecules to the oxide coating present on all common metal surfaces exposed to the environment which contains oxygen. Following application, the base oil [solvent not lubricant] evaporates leaving behind a chemically bonded molecular lubricant that will not wash off with solvents or water and is stable under extreme pressures and moderately high temperatures. Considering the exposure of motorcycle chains to particulates, mud, water, salt, sand and other contaminants, the fundamental property of a bonded dry lubricant is expected to maximize lubrication without retaining solids which can act as abrasives during operation. This is the fundamental property that makes DigiLube an optimum product for motorcycle chain maintenance. Other non-bonded lubricants like silicones and heavy oils/greases all suffer the problem of retaining solids and that is their characteristic weakness if chain longevity is desired.
Let’s consider automotive lubricants next. Motor oils are grouped into five classes which range from naturally occurring oils [Dyno juice = Class I] to Class V lubricants that are synthesized by reacting small organic molecules to form high molecular weight compounds. To be honest, as a professional organic chemist, the advent of commercially available Class V motor oils should eliminate consideration of using any other lubricant in one’s motorcycle. For that reason, I will not go into all the pros and cons of the Class I to IV lubricants as they are ‘antiquated’ relics compared to the superior properties exhibited by the one of the two kinds of Class V synthetics.
Class V oils are of two basic types: polyethers and polyesters. Polyethers are not typically used in conventional internal combustion engines as they are ‘sensitive’ to water and in some cases, even soluble in water. Polyesters are the cream of the crop from a chemist’s perspective when it comes to physical properties that are important to provide superior lubrication under extreme conditions of heat and shear. It is for this reason that I recommend using Class V polyester oils in motorcycle engines where the internal components are operating at high speeds, high temperatures with a moderately low volume of lubricant present in the recirculating system.
As mentioned, diol-based Class V synthetic oils can be synthesized in two formats depending on the initiator molecule. The most common is a diol [a molecule that has an alcohol group attached to each end of a hydrocarbon chain] that reacts with various dicarboxylic fatty acids to form long chain, linear polyesters. These are definitely better than any of the lower class lubricants in terms of their physical properties. However, there is a better molecular structure, one that produces spherical [actually star-shaped is more accurate] molecules which begins with a pentaerythritol initiator. These polyesters, being spherical in structure, provide the ultimate lubricant properties because of their resistance to breakdown under shear. Linear molecules tend to break which produces two chains of shorter length which leads to loss of viscosity and increased volatility. Spherical molecules can suffer a chain break on one of the arms but such degradation has a much reduced influence on viscosity loss because the fundamental molecular weight is reduced by a much lower fraction. While both types of polyesters have similar lubrication properties, those with spherical molecular structure offer significantly longer useful lifetimes from a chemical perspective. Because the manufacturers of synthetic motor oils consider their formulations to be proprietary, it is difficult to understand exactly what type of polyester you are purchasing. However, price per unit volume is often a clue. Lower priced Class V polyester oils are cheaper than the ‘high- end’ varieties that are composed of spherical molecules because of differences in the synthesis procedures employed. My personal understanding to date is the premium motorcycle oils [and automotive oils] from Amsoil are pentaerythritol-based lubricants which yield the spherical molecules I have described.
So, why are spherical polyester lubricants so effective compared to other motor oils? Pure hydrocarbons are designated non-polar while polyesters are polar. Chemistry teaches that “like dissolves like” which is incredibly important in an internal combustion engine. Combustion byproducts are partially oxidized hydrocarbons which range from carbonaceous solids to a vast variety of other polar substances. Pure hydrocarbon lubricants do not readily dissolve such polar by-products; hence the additives package of the oil must contain considerably higher concentrations of other chemicals to handle the lack of solubility issues. Such additives are not as resistant to degradation as the base oil and have a limited capacity which explains why cheaper oils have much shorter lifetime expectancies under operating conditions. While all motor oils, including Class V polyesters, have a substantial presence of additives to aid in preventing corrosion, adding lubricity, providing cold flow characteristics and viscosity modulation, the amount in the spherical molecular based polyesters is considerably less than all other such motor oils including the linear molecular based polyesters.
Polyesters are chemically very strong molecules compared to pure hydrocarbons and because polyesters are polar, they adhere strongly to metallic surfaces [compared to pure hydrocarbons] which is the primary reason they are such good lubricants. One notices this property when rebuilding an engine. It is somewhat difficult to remove the oil from parts as typical hydrocarbon solvents [paint thinner] do not readily dissolve it. In my experience, it takes acetone or methylene chloride to effectively remove it from a metal surface. Because polar polyesters dissolve most of the combustion by-products, the oil becomes dark and the internal metallic surfaces remain free of grunge that one encounters when using a pure hydrocarbon oil. The property of spherical molecular polyesters to reduce loss of viscosity caused by chain breakage provides significantly longer operational time between oil changes. Lower concentrations of additives to the base oil also leads to longer lifetimes as the base oil already possesses the necessary properties that the additives provide. Less additives means more base oil per unit volume, and it is the base oil that is the working fluid providing lubricity.
Bottom line: polyester lubricants have no competition when it comes to the chemical properties that are required for lubricating typical internal combustion engines. Those brands composed of spherical molecules are the best available option if ultimate performance as a lubricant is important. Amsoil, and perhaps some others, have such chemistry which is why I use them exclusively in all my motors.
OK, cool. So that’s what Toxic Terry says, and it sounds good to me, but what do I know? So I enlisted my friend Mr. Perplexity to do a little fact checking.
This is Deep Seek R1 (via Perplexity.AI), or rather here’s a link to my query and Deep Seek’s response. The link will open a local version of Perplexity for you. In the unlikely event you worry about opening your kimono to a Chinese AI the perplexity model is housed on Perplexity’s servers in the USA. Perplexity AI is owned by its founders, Aravind Srinivas, Denis Yarats, Johnny Ho, and Andy Konwinski, with a shit ton of outside money from Jeff Bezos and NVidia. I’m in the process of building my own Deep Seek server, just for the hell of it. https://www.perplexity.ai/search/please-analyze-the-following-a-_Zt57GG.SUKGUEnraaXjZg