Piston position and wet sump

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MikeM

MikeM

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I recall hearing or reading that piston position can help to slow down wet sumping during non use. True? If so what is the best spot? TDC?
Sorry to beat this to death.
 
I read that also and it made no sense to me. I'd sure appreciate hearing more on the topic.

Best.
 
The conrod journal would be at its highest at that point so cant do any harm.

I think oil might have an easier way back to the sump via the scavenge side of the pump including leaking from the pressure side.

Kommando sent me his drawings for installing seals an O Rings to the pump body which seem like a worthy mod.

Nothing can be beat to death based on being able to open a thread then hit the back button as suited.
 
I'll be interested to hear the opinions on this. I don't see why piston position would make any diffence. Wet sumping is caused by the oil leaking through the oil pump. The oil pump is a rotary gear pump and the leakage of oil through the pump will not be affected by the position of the gears when the engine stops.

Stephen Hill
 
It’s related to the position of the crank journal rather than the piston - which is of course hopefully attached. If the journal is at BDC or near the oil can drip through the crank by gravity and easily wet sump but if the journal is at TDC the oil has to climb uphill from the centre crank feed. Obviously as long as any hole is below the level of oil in the tank and there is some clearance in the oil pump it will eventually find its own level, but leaving it at TDC is supposed to delay this.
 
It's to do with the height of the column of oil, the lower the height the less pressure is applied to the leak point so the slower the leak. Same as your water pressure at your tap, the higher the water storage tower is the higher the pressure at the tap, the size of the tank has no effect.
 
On engines with oil supply to the pistons via a hole in the cylinder wall, piston position can affect wet sumping rate. E.g Vincents.
Not Norton related though.
 
Just checked my oil tank after sitting for over a month and NOT with the pistons at TDC. Oil tank is still 1/3 full and its because I have an oil filter between the oil feed line and the motor which adds resistance and inhibits wet sumping. This means that every time I change oil I have to temporarily disconnect the feed line at the motor and let the oil bleed through the oil filter so everything is primed (takes about 20 min with the hose hanging into an empty jar). It faster to use a section of clear hose and temporarily connect it to the feed line and pull the oil through to prime it.

Its routine now and I've been doing it for 30 years with no problems. No dirt from the oil tank can get into the motor this way. Motor has 50,000 miles on it, goes like hell and doesn't smoke (total seal rings).

The oil pump body has also been lapped to tighten up the gear side clearance.

Peeking into the oil tank on warm up after changing oil to view returning oil verifies that all is good.
 
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It seems to me that wherever the journals are, top, bottom, or middle, they will always be significantly lower than the outlet of the oil tank. So I can’t see why / how it would matter.

I’ve heard folk say it’s to do with the location of the oil holes in the conrods lining up with the oil holes in the crank. But wet dumping is caused by oil slowly seeping past the pump gears, which means we’re talking a very, very, slow dribble here, which will easily seep past the big end shells anyway (as that’s what they’re designed to do) irrespective of where the oil holes are.

Hence I can’t see it making any difference...
 
I thought the reason for the TDC was this leaves the flywheel in the crankcase taking up volume.
Doesn't stop wet sumping, just limits the volume.
With the pistons BDC or so the flywheel is higher allowing more oil to fill the crankcase.
Maybe I'm wrong but that's what I justified.
So do I do it? Sometimes, only when I remember.
 
With the journals in their highest position- TDC - the oil has to be raised higher to leak out so requiring more effort to get it there. Agreed that it is still lower than the tank outlet ( liquids seeking their own level, etc.) but every bit helps . A well lapped in pump provides the first line of defense . Perhaps best to think of parking the pistons at TDC as an aid to minimize wet sumping - not prevent it .
You haven’t experienced real wet sumping till you have lived with a big single . My ES2 is completely rebuilt with the pump fastidiously lapped in - to the point where you can barely turn it over by hand when not mounted in the timing chest - and it still wet-sumps with Morris 50w oil . I can state from personal experience that leaving the piston @ TDC makes a big difference in the amount I need to drain out of the crankcase before lighting it up.
 
Pistons at TDC ain’t gonna limit the volume as the oil will just fill up the cases more, all the way up the bore even !
 
The reduction in ‘head’ caused by the crank being at TDC cannot help because the restriction (the bottleneck in the ‘circuit’) is the pump, not the big ends.

So the relevant issue is the head of gravity between the tank and the pump and that ‘pressure’ forcing oil through the pump. What happens afterwards is irrelevant as it is downstream of the bottleneck. And the location of the pump, and tank, obviously do not change irrespective of crank position.
 
OK then I officially give up. From now on I'll just tell people I have a special start up splash feed device
for the cam installed.
 
Onder said:
OK then I officially give up. From now on I'll just tell people I have a special start up splash feed device
for the cam installed.
Click to expand...
Is the face between your pump and crankcases flat?
I ask this because one pump I had the cast iron flat piece (which the screws are screwed into) was sticking PROUD of the pump body, preventing the pump from being bolted flush to the crankcase. Some file time on the pump plate brought it back to the right place where it should have been in the first place.
 
Next time I'm in there to adjust the timing chain Ill withdraw the pump and recheck.
 
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