batman wrote on 04/23/20 at 08:20:25: Well we could debate this all day, but to think that the cam bearing just uses the lube is false , with temps of 3000 to 5000F depending on combustion ratio I' m sure the entire head is cooled by the oil. I will agree that if wear is present ,as in a high mileage motor that moving to a heavier oil may be necessary BUT ONLY if normal oil pressure can not be maintained. Use of 50 or even 60 grade oils over 40 grade in air cooled motors like the Savage is mute as the viscosity of these oils are the same at temperatures of 300F that the motor runs near. the Fact that 90% of wear occurs at startup make 20w50 a poorer choose when compared to 10w40 or 5w40 synthetic and may because of this cause added wear to an already worn motor . Oil pressure does not lube the cam bearings it is the flow of oil through the bearings that protect them,( the reason we don't idle the bike sitting on the side stand) and 40 grade oil will flow better and warm faster at startup.
90% of wear doesn't occur at startup - That is a total misrepresentation of reality. Yes 90% of non pressure lubrication occurs at startup. But cold starts typically are where clearances are high and the parts are cold and stationary before spun up.
90% of non lubrication occurs at startup.
Wear occurs at high temp and high speed where spinning parts swell from temperature, clearances reduce due to that and clearances reduce further due to centrifugal force causing the spinning parts to swell more and so on. This is why engines seize up on the road, and cars dying in the driveway typically die from electrical issues, or battery or gas flow where some obstruction freezes up and wont let it start, or rats ate the wiring etc.
I however agree with the need for higher viscosity oil if you cant maintain pressure with the lower viscosity oil though.
When the head is cooled by oil is considered, a higher viscosity oil would stay on the head a little longer before getting down the drain. As a coolant and cushioning agent higher viscosities are better as well. The only reason a higher viscosity oil is bad is if the pump can not build the recommended pressure with it where the pressure is needed - at the cam bearing in this case and where its splash lubricated at the cylinder wall
Basically the bottom line is - if the cam bearing oil pressure is inadequate due to the clearance being higher then higher viscosity would be a remedy. Possible side effect could be less splash lubrication onto the cylinder wall. All the rest is in favor of a 20w50 over a 10w40.
Cool.
Srinath.
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