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Continued......................
Please can you explain the grading system? What is meant by the weight of an oil? What does 10W/40 mean for example?
Weight means viscosity, or resistance to flow. Water and paraffin flow very easily, so they are low or light viscosity. Golden syrup or 140 gear oil do not come out of the can so easily, so they are high or heavy viscosity. Especially with oils, temperature is very, very important. An oil which looks ‘heavy’ at 20C will be very ‘light’ at 100C. People sometimes say, ‘I drained the oil when the engine was hot and it ran out like water…’ so I say, ‘Good! It’s supposed to be like that!’ The American Society of Automotive Engineers (SAE) ratings cover cold starts and ‘up and running’ viscosities.
There are two sets of standards, the ‘Winter’ (W) ratings, and the 100C standard ratings. (‘W’ does not, repeat not, mean ‘weight’!) So a 10W/40 oil has to pass a 10W cold viscosity test at -25C, and a SAE 40 test at 100C. In an oil lab there will be a refrigerated viscosity measuring device for the ‘W’ tests and another at 100C for the standard SAE tests. There are 6 ‘W’ ratings from the difficult 0W at -35C to the dead easy 25W at -10C, occasionally used in India for example!
The whole point of these Winter ratings is to assist cold starts, to get the oil circulating quickly, and to avoid power and fuel wasting drag as the engine warms up. Once it is warmed up, the 100C ratings count. There are 5 of these, 20, 30, 40, 50, and 60 although why anybody bothers with 60 in the 21st Century is a mystery to me!
Sorry folks, but I’ve got to get technical. Viscosity is measured in standard units called ‘Centistokes’, names after a Victorian engineer, Sir George Stokes, who used to time ball bearings as they sank through oil. SAE 30 for example is from 9.3 to 12.5 Centistokes, and SAE 40 follows on at 12.5 to 16.3, although most SAE 40 oils are in the middle at about 14.
Now this is something most don’t realise: engines do not know what grade of oil they’re running on. They’re not clever enough! So an engine filled with 10W/40 will be running on a viscosity of 14 at 100C, but with a sump temperature of 90C its seeing a viscosity of 18, so as far as the engine is concerned it’s running on SAE 50. Likewise, at 110C, it’s down to 11 Centistokes so it ‘thinks’ it’s on a SAE 30! (Which is preferable.) The lesson is, do not use power and fuel-wasting thick oils in cool climates.
A decent 10W/40 or even thinner is perfectly OK unless you’re riding an air-cooled classic with wide clearances and a slow oil pump.
Radical race cars use 1300 Suzuki Hyabusas and work them very hard. (Didn’t one take the old Nurburgring absolute record recently?). They use our high-ester 15W/50, but that’s OK because they see oil temps around 130C! (No problem for the oil or the engine, but they do fit special oil seals.) At 130C the true viscosity is 10cSt, so the engine thinks its on a thin SAE 30, which keeps it happy.
What is the best type of oil to use in a road bike for general riding? Is fully synthetic a waste of money?
Personally I’d go for a shear-stable ester semi-synthetic, SAE 10W/40 or 10W/30. The ‘shear-stable’ bit (ie, a decent quality multigrade polymer) is actually more important than the ‘synthetic’ part! If strapped, I’d go for a shear-stable mineral based oil rather than a ‘synthetic’ of dubious stability that’s probably based on modified mineral oil anyway. Unless you’re covering a huge annual mileage, genuine 100% synthetics are probably an extravagance. High mileage long-distance fans can use a light full synthetic and save on fuel and oil changes, and cut overhaul costs if things get to that stage, but more later…..
What are the main differences between 2 and 4-stroke oil? Why does 2-stroke oil have to be mixed with fuel?
2-stroke oil has a very short working life, straight in and out, and it gets burnt. The 2-stroke engine doesn’t have a sump full of oil and the bearings are all rollers, so there’s hardly any oil drag, hence no need for multigrades. Long term stability is obviously not a problem! But, 2-stroke must burn off without leaving any plug-fouling or detonation-initiating deposits. The detergent and anti-wear additives used in 4-stroke oil leave hard white ash behind when they burn, just what you do not need in a 2-stroke. So 2-stroke oils use low-ash detergents and dispersants, and the better types use ester synthetics to act as anti-wear compounds.
With current environmental concerns, smoke is a sensitive issue, so most ‘road’ 2-stroke oils are now low smoke, which requires yet another type of synthetic base designed to burn off invisibly. For some rather basic but very high-revving air-cooled racing 2-strokes there’s still some sense in using blends with that marvellous anti-seize liquid, castor oil!
Due to crankcase induction and compression, the classical 2-stroke obviously cannot have an oil-filled sump, so the only way to keep an oil film on anything was to add oil to the fuel, or inject oil into the crankcase space where it could mix with the fuel vapour. There are now some engines where the fuel and oil are injected separately, but the oil is still burnt.
How important is it to change oil regularly? What are the implications of failing to do so?
It is only really important to change oil regularly if the bike covers a low annual mileage made up of slow, short runs. This is being cruel to the oil and the engine! The oil, regardless of its quality, gets full of fuel and water vapour, and never gets the chance to evaporate it all off with a long fast run. The consequences are corrosion, ring and bore wear, and gear tooth pitting. It is essential to do a change at least once a year, even if the recommended mileage hasn’t been covered.
On the other hand, if you eat up the miles on long blasts the engine and its oil will love it, so with a top-quality oil it is OK to cheat a little on oil drain periods.
Do some types of oil (i.e. fully-synthetic) ‘wear out’ quicker than others? How important are timely oil changes? Can you rely on the frequency suggested by your bike’s User Manual?
(Your enquirer has got it arse about face!) The type of oil that is likely to give trouble after low mileage is a light viscosity non-JASO MA type with poor shear stability, either mineral or modified mineral based. (Such as one of the USA ‘fuel economy’ oils for lazy car engines that pushed the Japanese OEMs to bring in their own oil spec.)
The important thing is the shear stability; the much hyped ‘synthetic or mineral’ nonsense is a red herring. The oils that will last the longest are the relatively rare 100% genuine synthetic shear stable types, which will easily stand twice the recommended drain period in a high-mileage high performance bike. (So in the long run they aren’t really so expensive.) Just the thing for those touring fiends who pack the panniers and set of for the Transylvanian Alps as soon as the clocks go forward! (Fancy an oil change in L’Viv?)
Of course, User Manual drain recommendations are based on a back-covering ‘worst case’ scenario of low annual mileage on poor quality oil, so they can be regarded as a very safe minimum mileage.
In the past, there used to be trouble with heavy carbon deposits and sludge around the engine with early low-detergent oils, but these days almost any oil with a good API specification will keep everything clean for 10 to 15,000 miles, so that’s the least of your worries.
Does oil have to be warm to do its job properly? Is it important to warm up your bike before riding at speed?
Yes, it does have to be at least warm, and preferably hot. Most people except vertical twin riders with white finger syndrome find metal at 60C too hot to touch, yet 60C is too cold for oil in an engine that’s going flat-out. The best approach is to use a good 10W/40 or even a 5W/40, and take it easy for the first couple of miles, especially in very cold weather.
For racing, a really good warm-up is essential, except perhaps with special 0W/20 low-drag race oils. The trouble is, oil pumps are very good at pushing oil out at 60PSI, but unfortunately there is only 14PSI (atmospheric pressure) pushing it in! (Even less in Katmandhu.) So it’s easy for an oil pump to pull voids or pockets of vacuum in the oil if it doesn’t flow fast enough into to uptake. This ‘cavitation’ obviously reduces the amount of oil the pump can deliver. Also, in high-speed bearings the oil can be too thick to keep up with the high rubbing speeds reached in modern engines so the ‘wedge’ or hydrodynamic’ effect breaks down.
I know it goes against common sense (whatever that is) but the faster a bearing is turning the thinner the oil should be. (A 4cm. diameter main bearing is rubbing its shells at 56 MPH at 12,000RPM! To avoid cavitation the oil need to be less 10cSt or less, which is SAE 30 if the oil happens to be at 100C, or SAE 40 if its at 110C.))
What is the difference between road and racing oils?
The days of incense-like ‘R’ oils for racing only are past, except for classics. At least as far as 4-strokes are concerned, the best synthetic types are ideal for both race and road use. (Well, that’s our policy. All of our race oils are on the retail price list!) With ultra-precise components, high-pressure pumps and high engine RPM there has been a move to special synthetic low cavitation/low drag oils to release more power with no reliability loss. These can be (and are!) used in road bikes, but 0W/20 is not mentioned in the user handbooks, so there is always some warranty risk.
How does a high-performance oil allow the motor to produce more power?
An engine wastes fuel energy in several ways, and most of them are due to the laws of thermodynamics, which is another way of saying you can’t do much about it. But up to 6% of engine output is lost due to oil drag, made up of pumping losses and viscous drag between moving components. The transmission is included in this in most motorcycles. Provided wear and friction are kept down, there are real gains to be made by using a ‘tough’ but low viscosity oil. Surprisingly, frictional losses are low, down at 3% or less even with conventional oils, so there are few gains to be made here.
I have actually seen this extra power output on the dyno! A very experienced operator in Peterboro who does a lot of test work for Lord Emap used his own year-old Honda Blackbird, with the first run on his favourite 15W/50 high-ester synthetic. 128BHP.
Then we changed to a 5W40 high ester synthetic. (So it wasn’t an unfair comparison with B & Q 15W/50!) This time we saw 131.6BHP with a corresponding torque increase.
Finally we went to a new (at that time) 0W/20 special synthetic and 134.4BHP appeared!
Even the boss was impressed! Later trials in different race and road bikes showed this level of improvement was no fluke, so it really does work; and, with the right chemistry to look after the engine and transmission internals, there’s no down side of increased wear.
Why do some engines consume oil? Is this a problem?
Large air-cooled engines with wide piston clearances, or very highly stressed liquid-cooled engines which flex under load, or which use ultra-light pistons with the minimum number of rings are likely to be oil users. There is little that can be done about it. Unfortunately, burnt oil tends to leave hard deposits in the combustion chambers which can initiate pre-ignition, so more frequent top overhauls are usually necessary.
Occasionally, touring engines will use oil for no apparent reason. This is often due to the oil level rising in the crankcase due to air retention, leading to oil loss through the breather. The answer is to move to a lighter grade of oil to improve air release.
If you need to top up your engine oil, how important is it to use exactly the same brand and type?
Not very important at all. Unfortunately, due to ‘arse covering’ reasons we cannot print this advice on the can! Although officially all manufacturers advise against mixing different makes and grades, in fact there is very little chance of any harm being done, even if one is a mineral 20W/50 and the other is a 5W/30 synthetic. Obviously, avoid this if you can, but do not panic if there’s no other alternative. Just don’t mix 2 stroke and 4-stroke oil!
There are all sorts of additives available which are supposed to improve ordinary oil and reduce friction, improve power output etc. Are they worth a try?
Oil is already a very advanced and deeply researched fluid which does not need any ‘enhancement’. There is no secret formula out in the backwoods that the mainstream lubricant chemists do not know about; but there are plenty of half-baked ideas and gullible people out there! These wonder additives are usually 1930s chlorinated paraffins, long obsolete gear oil additives which should have disappeared in the 1950s, but they keep turning up as ‘Xxtrasuperlube ZX3’ with a mark-up of several thousand percent.
They actually corrode engine and transmission internals, so they do far more harm than good. Others depend upon the total myth that PTFE powder coats engine internals and reduces friction. It doesn’t do anything or the sort. It just blocks the oil filter. The AA tested one of these overpriced PTFE concoctions (‘Quick 60’ or something) very thoroughly back in the 80s. They stated: ‘This is an expensive way of coating your oil filter’.
Cheers
Guy
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