Oils

November 17, 2009 by mike.cox

What oil should you use?
Now this is a subject that has caused more discussions and sometimes arguments than anything else combined has.
If you have definite thoughts on this subject, then bypass this article.

First a few names and numbers which will rectify some of the misnomers floating around.
SAE is the ‘Society of Automotive Engineers.
The W in 20W50 or W40 etc stand’s for winter.
API is the American Petroleum Institute.
 
Generally after API is a two-letter designation. SF. SG. Etc. the S stands for ‘service level’ the second letter, which can be from A through to L. The higher up the alphabet, the better the oil is.
Although I’m told ‘S’ stands for spark?
 
Taken from the internet. (The viscosity of petroleum-based oils decreases as its temperature increases and conversely, viscosity increases as temperature decreases. Limits for fluid viscosity and fluid temperature must therefore be considered simultaneously. Low fluid viscosity causes loss of lubricating film strength, which leads to boundary lubrication conditions, scuffing and adhesive wear. Excessively high fluid viscosity damages system components through cavitation.)
This was from an engineer.
 
I haven’t bothered going into ‘stokes’ or ‘centistokes’, which is one of the units of measurement for the dynamics of fluids.
 
Now with that over, we can start.
 
Almost every oil whether it’s a monograde or multigrade has additives included to improve oil performance.
It is sometimes hard to believe but up to 40% of multigrade oils could be additives and not mineral oil at all!
 
Multigrade oils generally have stronger cleansers included that will take deposits that have laid in crannies inside the engine and oil-tank, into suspension and become part of the circulating oil, that a monograde most probably will not to the same degree. As most of these multigrade oils are used on cars, which have an oil-filter, this is no great shakes, but when the engine has no oil-filter, well I leave you to ponder this.
 
If the engine is brand-new, the big-ends are white metal, every orifice has been cleaned to operating theatre specifications, then I would recommend multigrade without hesitation.
Multigrade is better oil for white metal bearing engines, especially when first starting up and similar in viscosity to monograde under very hot conditions.
 
These different viscosities of oils, whether monograde or multigrade are quite easy to understand.
Monograde oil specified at 50 or to be more correct SAE50 is exactly that. 50 when cold.
It will get thinner as the oil heats up.
A multigrade specified as SAE20W50 is a 20 viscosity oil when cold and also gets thinner as the oil heats up.    
This multigrade oil uses a base oil to start from, which is SAE20.
I’m using the word viscosity in a more general sense.
 
Both end up with very similar ‘viscosities’ when taken to the same hotter temperature, usually measured at 100 degrees Celsius. To make the multigrade oil seem like 50W oil at high temperatures the oil companies add ‘polymers’. These are long-chain molecules that bind the base oil molecules together as they become hotter. Cool them down and they reduce the binding action and you have 20W oil again.
A sort of ‘polymers holding hands with the base oil when hot, but letting go when cold’.
 
The advantage of the multigrade oil is the cold oil is thinner, circulates easier when first starting up.
To get the same effect with monograde oil, you would have to start with much thinner oil, and lose out when the oil gets to operating temperatures.
 
Be aware, any oil made for car engines also has modifiers included to reduce friction. (Car companies sell cars on fuel efficiency and by far the biggest users of motor oil) look for SG or better specs not SF on the container. This is especially important if the gearbox forms part of the engine and uses the same oil where oil films can and will shear as the gearbox teeth come together.
Such as most Japanese and Ducati bikes for instance.
Oils sold for ‘older’, hard working or high performance’ engines are usually of SG grade.
 
Some people recommend Diesel grade oils. These oils have the highest protection levels but also I believe the most detergents added because of the high sulphur content in the diesel fuel. This is a general statement. Some diesel oils have been specified for use in specific vehicles with much lower detergent additives. You can also get these diesel oils in SL grade.
I have no personal experience using these types of oil, but I’m nervous to become a guinea pig. I would also say, rather not try these types of oil unless you have good knowledge of what you are doing.
 
BMW, the bike company, did a survey of every well know oil brand in America. The diesel oils didn’t come out very good in BMW’s.
 
If you have access to a computer and modem then there is information on the Internet about this subject.
 
There is also a wealth of information available about using multigrade oils in classic bikes that run ball or roller big-ends or main bearings.
90% of these individuals who have looked into the subject are very strongly against multigrade oils for these bikes.
They reason that ball or roller bearings need a type of oil that does not shear to the same degree as multigrade oils do at operating temperatures.
 
They go on to say that multigrade oils when hot, flow far faster and do not give as much protection to the races, as would monograde oil.
They also say the balls or rollers tend to skid within the races, causing premature wear.
I tend to agree with them and do not use multigrade oils in the AJS or Ducati.
 
Lastly, they say that where bikes have common oil for engines and gearboxes, the multigrade oils break down to a greater degree when passing between rotating gears such as found in gearboxes. (They call it polymer chain breakdown).
 
So as the oil is being broken down, what first started out as a 20W50, could be as low as a 20W30 after 5000Km.
(Remove or destroy the polymers and you end up with the base oil).
 
Most oil companies tend to agree with this hypothesis, and recommended that oils should be changed more frequently if multigrade oils are used with ball or roller bearings.
They were sitting on the fence a bit, as they sell all types of oil.
 
When a bike has plain big-end bearings, you definitely need oil that keeps the shells away from the crankshaft, and this is where multigrade oils are at their best.
 
Don’t shoot the writer; he only made it all up from a bad memory!

What oil should you use?
Conclusion.
 
Synthetic oils
Locally available Synthetic oils didn’t seem to work to the degree expected in the engines I’ve built. Sure, I believe they give extreme performance and stop dead any high wearing areas such as camshaft to cam lobes etc, but I’ve always ended up with high oil consumption.
 
That’s after a proper running-in period using normal oils. In addition, at >R250.00 for 4-litres, I can do without topping up every few hundred miles or so, that’s if you can find a can available at a garage out of town.
Didn’t run the engine in long enough I hear you say. How about 12,000Km on my Kawasaki VN1500 which never used a drop of normal oil before changing over and I gave it another 2500Km to settle down as well!
The only way oil can get burnt is either past the rings or down the guides. The thinner the oil, the easier it can flow past control points. I.E. rings and seals.
John Boswell used Synthetic in one of his racers and was black flagged for pouring smoke out the back. Turned out to be glazed bores from the oil.
 
Synthetic oils do keep their specifications far longer than any other type of oil. Oil-changes can exceed 20,000Km without harm.
 
Every piece of machinery that uses oil as a lubricant gets the most wear when first starting up. Not only the first time after a rebuild, but also every time, you start the cold engine.
Because we only take our historics / classics out, possibly once a month, the oil protecting moving parts would have drained down, leaving many parts with minimal oil protection on start-up.
A bike ridden every day doesn’t have this problem anywhere near to the same degree.
 
When we get to the gearbox, most of us use EP90 gearbox oil because that’s what is sold for gearboxes for our cars!
EP90 has the same flow characteristics by the way as 50W.
EP stands for extreme pressure.
 
In the newer separate motorcycle boxes, this is fine, but I am told older boxes (<1970’s) have a type of phosphor bronze bush that is attacked by the additives in EP90 gear oil. If the workshop manual specifies engine type oil, then rather use it. This is usually SAE50W monograde oil.
 
I have heard of individuals using R40 vegetable-based oils in separate gearboxes without harm.
  
Morris oils in the UK mention in a pamphlet issued to interested parties about oils in gearboxes.
They say EP90 gear oils will eventually cause notchy gear selection and increased noise in gearboxes manufactured prior to 1970.
 
Lastly, before we leave oils, there is the subject of castor-based oil.
Commonly called Castrol R, it is vegetable based oil that gives extreme shear strength on surfaces rubbing/ moving passed each other.
This was the oil for racing engines in the past. Usually now only found as a SAE40.
 
You cannot mix castor based oil with a mineral or synthetic oil, gumming up will occur in short time if you do, and serious engine damage will result.
I am told there is no advantages whatsoever to running a historic/ classic on ‘R’, unless you intend to race the historic and then I would consider using a synthetic if you have plain big-ends. However quite a few members use R without any trouble whatsoever.
 
You can purchase a small bottle and put an egg cupful into a full tank of petrol just for the smell though. It’s not cheap for the smell at R60.00 a litre.
Alternatively, ask a member who’s done an oil-change if you can have some of his old oil.
 
Engines running on ‘R’ need proper warming up before riding off.
 
Castrol R40 is not cheap. The price from Castrol in Roodekop, Johannesburg was R58.00 per litre and that was a year or so back. Minimum quantity is 10-litres. (Dated May 2003.) However, Castrol for whatever reason often do not have stock and 3-4 months delay is common.
 
Lastly, R40 cannot be left in engines for extended periods of time. So if you run your historic on R40 and only change the oil every two years or so, you are looking for trouble!
 
Removing Castrol R from an engine, so a mineral oil can be used.
All the books and wise men say you should strip an engine and wash thoroughly, all the internal parts.
This is the correct and only way of removing residual traces still in the nooks and crannies.
 
What about additives?
Personally I wouldn’t use additives, ever.
Why? Well for one the oil you’ve purchased already has additives added. The amount of additives, and there are many different additives of very small and differing amounts mixed together to give the best protection the oil company believes is correct for the type of oil it’s promoting.
Now you come along and add another additive. This will upset the mix ratio of what’s already there. Now a particular type of compound that worked as specified, is modified and could become a potential problem.
 
But if you do,
First thing, do not add any additives whilst the engine is running in. By that, I mean for at least the first 3000Km.
The engine needs to rub all the high spots away where moving parts slide against one another.
 
The additives will slow down and possibly stop this bedding-in and you’ll end up with high oil consumption forever.
 
Well there have been and I suppose will continue to be offered, many additives that will reduce wear (their claim), up to allowing the engine to run oil dry without major damage.
 
Additives are already in good quality straight and multigrade oil and there was one very well documented court case in the USA where these additive companies (called snake oil companies in the States) took Du-Pont, the maker of the base material for 99% of these additives, forcing Du-Pont to continue supplying them, which was upheld in the Supreme Court.
 
Du-Pont after losing the case took out many full-page advertisements explaining that in Du-Pont's view, they believed harm could come to engines using these products, the reason why Du-Pont wanted to protect its name and stopped supplying in the first place.
Du-Pont was not saying these additives do not reduce metal-to-metal friction. Tests have proven that they do.
The contentious point was that as these additives heat up, their change in make-up causes the molecules to become elongated and can block filters and possibly small oil-ways if enough is mixed with the oil.
Some additives will also cause the wet clutch to slip.
The choice is up to you.
 
N.B.
I used to put 2 to 4 moth-balls in my petroltank when I was a lad. It works quite well and gives this lovely smell of naphtha. That’s a mothball smell to you uneducated lot!
Also it will keep all but the quicker moths from overtaking the slower race machines!