I was waiting for someone to ask that question. I doubt one-way crankcase breather valves approach a vacuum, at least not on our Nortons but one of the advantages to reducing crankcase pressure (I mean serious pumping to evacuate the crankcase) is reduction of windage. Wind is comprised of air and when you reduce or eliminate the air, the oil droplets tend to fling and set rather than get "air" transported all over in a circulating load. Another advantage to significantly reducing crankcase pressure is increasing the differential pressure across the rings which I understand enhances the sealing of the rings.Just a thought but crankcases with one way valves approach vacuum . Is oil vapourisation different from what it would be at atmospheric pressures..In a vaccum water boils at room temperature .
Ken,
What oil did you use?
With or without Zinc?Penrite 20-50 motorcycle oil.
Aye!With or without Zinc?
With or without Zinc?
Plenty.
No, a flood is not better. Rod bearings rely on a hydrodynamic wedge which occurs under controlled conditions of load, oil pressure, speed, viscosity, and probably a half dozen other thingies.
Penrite has plenty of zinc.Plenty.
I use 10/60, it never gets thicker, it's like a 10 when cold and a 60 when hot but that is still thinner than a cold 10, a hot 75 would still be thinner than a cold 20. The difference between the 2 extremes will be less but the hot oil will be thinner, just not as thin as a 20/50.
I am wondering what was left out of the 20-50wt that Ken was using with what penrite recommended for Pre 1980 engines. It lists plenty of M/C:That looks like good oil IMHO.
25w70 is an interesting weight. I am a believer of thick (when hot) oil in our slack old motors.
But this oil makes me wonder, at what point does thick become too thick?
Penrite has plenty of zinc.
Just for fun, I went on there website and scrolled through what they recommend for oil for a Norton Commando. They listed this:
https://penriteoil.com.au/applicati...MANDO&year=1974&fuel=PETROL0.8&vehicle=204017
The zinc numbers are higher as well as the Phosphorus, Mass %. It is also recommended for pre 1980 engines.
Ken, did you get the oil analyzed just to rule it out of the equation?
The mystery continues.
Thomas
I will be looking out for these photos for sure.This coming winter, my friend is pulling apart his 128,000 mile, purchased new, never been apart 73 850 engine for a complete rebuild. Its going to be interesting to see that cam and followers.
Will post photos of it and anything else of interest from that engine.
Glen