L.A.B. said:
Well, you appear to have completely changed the subject!
Well, I'd
call it "broadening it's aspects a little" ....
L.A.B. said:
Running the engine with the sump constantly full of oil for 10 minutes! without the scavenge system working correctly hardly seems to be anywhere near the same thing (which was the scavenge initially clearing the sump of excess oil on start-up).
IMHO there is no such thing as "the scavenge initially clearing the sump of excess oil" if the oil quantity in the crankcase is
really excessive. Particularly when the crankcase oil level is significantly above the crank's bottom dead-centre position the pump can't get it out at once (no "big gulps" there). In consequence, it is whipped to a foamy froth. OTOH, if the crankcase oil level is lower than that, there's no oil in the sump that is "splashed" about and thus none of it will ever hit the cam lobes.
In consequence, you have a "wet sumping" problem if
a) the scavenging side of the oil pump can't clear the sump (which ought to be dry anyway) after approx. ten minutes, and
b) this aforementioned observation makes clear that an "initial clearing at startup" did simply not happen, and
c) after thorough verification of the engine and some conversatons with the PO there are identifyable causes of the problem:
- worn-out oil pump causing oil tank drain into sump;
- PO's unawareness / neglect exacerbating the problem;
- use of cheap low-viscosity mulitgrade oil further exacerbating the problem.
L.A.B. said:
From what you initially said concerning cam lobe lubrication and possible poor sump scavenging on start-up (possibly caused by foamy oil?) causing oil starvation to the pump supply as a result of *wet sumping* (as you understand the term) now seems to be caused due to a problem of a faulty pump and the use of incorrect oil causing a *wet sumping* (as I would describe it) problem.
I am afraid that you have mis-interpreted what I originally said. I have simply pointed out that a dry sump full of oil ("wet sump") isn't a good thing at all, even though it might provide some added cam lobe (splash) lubrication. I have then pointed out that if the oil tank drains down into the sump, there's so much oil in it that it can get easily whipped to froth, rendering the scavening side of the oil pump almost completely useless.
L.A.B. said:
Obviously these two different examples of *wet sumping* show that it can mean two different things! This latest example having nothing really to do with what we were originally discussing?
From a highly "hypothetical" view, there's a difference. In practice, there isn't. Pls. see below.
L.A.B. said:
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= Wet sumping?
Either
Sump over-filling due to gravity draining of the oil supply to the sump.
Or
Failure of the scavenge system to clear the sump of oil while the engine is running.
Perhaps it would be a good idea if these two totally different conditions were to be called: static wet sumping? And dynamic wet sumping?
If ultra-precise terminology is what you're after, please feel free to do so. However, most gear-type oil-pumps (and the Commando pump is no exception) allow oil bypassing when "static", and are also unable of doing their scavenging job appropriately
when they are worn out - and even more so if too much oil has drained into the crankcase, getting whipped to a frothy foam there.
Of course there are other causes of scavenging-specific malfunctions:
- metallic debris caught in the pump;
- oil scavenging holes / pathways plugged.
I haven't yet encountered any of the latter problems, but usually found generally worn-out oil-pumps, showing both "static" and "dynamic" wet-sumping as well as very low oil (feed) pressure when warmed-up. The case I described was a grave one since the PO was not familiar with old brit-iron at all and thus exacerbated the problem.
So what I have been saying (and still do) is that "wet-sumping" is a
multi-faceted, self-exacerbating problem - and ist doesn't come along with any
real advantages, not even hypothetical ones. Hope this helps.
