The C90 was never designed to sustain full speeds for hours on end so it doesn't cool as well as the Innova models, which are expected to be used at modern traffic speeds. As a consequence, sustained high speed riding on a C90 can overheat it to such an extent mineral oils will simultaneously cook while failing to fully lubricate the hottest engine parts, leading to smoking engines. , The over-heated oil then cools once the engine has stopped and thickens (which is a characteristic of abused mineral oils when the additives burn away) this means subsequent starts from cold are even more poorly lubricated, leading to more ring and guide wear.bigswifty wrote:Jon/Tim, thank you, your information and knowledge is greatly appreciated. I do not have technical engineering or chemistry knowledge and often curious regarding oil. As it's sort of a 'taboo' topic on the forum (I imagine due to the wide variance in opinion and subjective view), it is hard to determine 'best selection' for the little revvy engine. I have favoured mineral 10-40, though it may be the case more advanced oils provide better lubrication and protection. With admin approval, I would support and welcome Expert/Guru advice regarding oil (I DO NOT WANT TO SPARK A ROW)(CLARITY ONLY)
again, going back to the cold starting, 10w-40 takes several miles to thin enough to reach the viscosities the engine is designed to use. The bike will run fine of course, but because the engine is so small and works hard in the UK, the heat generated at the rings needs to be cleared and fast flowing correct viscosity oil has a large part to play. if the oil is too thick, it flows slowly and those components rapidly overheat, cooking off the film of oil that is lubricating them and so you again get wear.
In it's original markets,, like Vietnam, the Cubs used to be used at lower engine speeds often for greater distances and in those cases the recommended 10w-40 oil is fine...
With conventional oils, as much as 90 percent (it is said) of ALL engine wear happens when the engine is cold so minimising the time the oil is too thick is key to engine longevity. Engine service life can be gauged by the ratio of miles used when the oil is too thick versus when it is at correct temperature. With short journeys, the engine could easily spend ALL it's time with oil too thick and the engine will wear fast, and be ready for a new piton and rings after 20,000 miles or so, whereas with long journeys, you might get 5 miles of cold running and 95 miles of hot running. That particular engine will last a very long time.
We have all seen this with cars that do high daily mileages compared to cars that only go a few miles every day. It was not unusual in the past to see otherwise mint old cars with engines shot with 40,000 miles or less on them, yet the 'rep' cars, with their many full temperature miles on the engines might rack up well over 100,000 miles and still sound and behave as new. Back in the day when the first VW Golfs were around, it was common for them to be smoking after 60,000 miles. that was entirely down to cold start wear as very few Golfs were chosen as business cars....And don't forget, a car has 4-5 litres of oil to warm up before it is good to go flat out...i suspect a Mk1 Golf GTi would last MUCH longer running a 0w-40, even over regular short journeys.
I also believe Hondas have small sump capacities to allow the oil to rapidly warm and also believe that oil coolers without thermostats will increase cold start engine wear as they constantly cool the oil instead of doing what a thermostat does which is only engage the oil cooling radiator once oil exceeds its working temperature.
The end result of all this is that if you like to use your Cub at full speed, to stay with modern traffic, you need a synthetic 40 to cope with the overheating, and if you only do a few miles like that every day, then ideally a 0w-40 which will reach the required thinness much faster than 10w-40.
Again, this only applies to people who ride hard. If you are pottering through traffic during your commute, or bimbling about at weekends for fun at 'smell the countryside' speeds, the recommended oils will keep your engine as healthy as a full synthetic.
It's down to engine load, or how hard the engine is working to sustain your speed. At full speed, the engine is trying to dissipate the heat by-product of the full output of power and in the Cub's case, it isn't designed to do that. Gentle loading until it is warm, and infrequent full loading when up to temp will keep wear low with conventional oils.
Even with synthetics you shouldn't thrash the motor under full throttle for a few miles but it'll drop to the correct viscosity quicker AND protect during sustained full throttle use.
For many of us, who trat our bikes as weekend playings, all this is largely irrelevant, but if like me you commute on a cub and rack up the miles with many shortish, high speed journeys (i do about 7000 a year of 12 mile each way a day runs)...It makes a difference!