Engine Oil

Friction modifiers primarily. Wet clutches hate them.

 

With car engines the clutch doesn't share the same oil; whereas on most bikes they do. This is a change of use which requires changed oil specs.

 

Car oils are made to be as slippery as possible to reduce friction, not ideal properties for a wet clutch

 

Same spec or same viscosity?.......not the same thing.

Quote us an SAE Spec, API or JASO spec.

 

One of the problems here Callumity is that specifications such as SAE are very broad so two quite different oils can be classed same. A military specification is far tighter and specific.
Otherwise I agree without a specification it is impossible to compare.

 

Yeah well the military tend to over specify and over service!

 

Can you over specify IF you know exactly what you want?

Obviously they have the funding and/or the might to get what they want.

 

Well sometimes the best is the enemy of the good because expensive stuff designed to outlast arduous combat use and obviate field maintenance gets poured away barely used and money IS an issue.

There is more diagnostic oil testing these days - especially for aircraft and big propulsion units but, like bikes, a semi-synthetic will lubricate just as well as a fully synthetic for typical mileages and annual oil changes and cost less. The fully synthetic comes into its own in higher temperatures and longer service intervals.

 

From Mobil US website:

Motorcycle oils and passenger car oils are very similar, with the exception of a couple of areas that are key to motorcycle operation. The first area concerns common sumps, or the use of motor oil, to lubricate and cool the transmission. As you know, in a passenger car the transmission is lubricated by an ATF fluid, which has frictional properties required for transmission operation. In a motorcycle, where the engine oil may lubricate the transmission, an engine oil that does not have the same level of friction modification (for fuel economy) of a typical passenger car engine oil will provide better transmission performance in terms of transmission lock-up and slippage. So motorcycle engine oil does not contain the friction modifiers of a passenger car engine oil. The second area of concern for motorcycle engine oils is that they tend to shear (break down viscosity) more quickly than a typical passenger car. Mobil 1™ motorcycle oils are designed to provide exceptional protection against viscosity loss.

 

Used all sorts of oil, car or bike even 20/50 in the A10 will no ill effects

 

The problem with that statement is that its referring to ATF automatic transmission fluid (makes sense since its US) ATF is totally different to engine oil, other than the friction modifiers/additives mentioned previously there is no difference in car and motorcycle oils.

 

Agree a no-no to use car oil on a bike. Bike oil needs to do 3 things (different from a car) . Lube engine, lube gears and wet clutch operation. And clutch will slip if car oil is used.

 

Also ran my VTR1000 on car oil - Castrol Magnatec! No ill effects. Ran my K75s Beemer on Magnatec for 20+ years too. Again no ill effects.

There is no way an oil company is going to admit that oils are the same when they are charging extra for 'motorcycle' oil.

 

I haven't used car oil in bikes so can't comment on that clutch issue but.....

For years I have used atf in off road bikes. Other mates have discussed, and prefer, modern synthetic 75 gear oil. Strangely you (I) cannot use just any atf. I found this out by buying a gallon of cheaper stuff when my preferred Motul wasn't available. With off road bikes the clutch operation is significantly affected by your choice of oil and I always found Motul to give the best snatchiness and abruptness.
On the Montesa 315s (1998 - 2002) the clutch has some paper plates (No not what you have at barbeques!) and a definite tell tale that the gearbox oil was going off was a squealing clutch when on significant load.

Personally I don't always use the noted oil but I wouldn't use anything that I had doubts over concerning the clutch.

A £10 saved on oil isn't going to buy me a set of clutch plates. You may or may not agree but that's fine as I'm not buying your plates

 

Dilligaf, help me understand your disagreement. Clutch slippage? I know of clutch slipping issues w/ car oil. Car oil does not belong in a bike with a wet clutch.

 

I disagree with it because I’ve used car oil in motorcycle engines in the past and never had any problems with it most notably 1200 Bandit and Fazer 1000
And two kwaka GT 750s
This has been when I’ve been hard up (most of my adult life) and have been unable to afford oil bottles with a picture of a motorbike on the side

 

When it comes down to it the clutch type and friction plate materiel is going to determine whether its going to slip when using car spec oil IE with extra friction additives, so some will be fine while others will slip other than that it makes no difference.