Breather Experiment

I have installed a breather on the timing side of the crankcase while retaining the one on the lower left rear.
I have also purchased an old oil pump off ebay. Although old, I found the gears and internal surfaces very fresh, night and day compared to the unit removed from the bike. It took little work to bring this pump to like new, operationally.
I have also reverted back to the original timing cover after trying a MKIII unit. I thought that this MKIII cover would help with oil draining from the tank. I think it made it worse. The access cover for checking the timing chain was good and it helped me identify crank pressure issues, but it just wasn’t worth it. The new (older) refurbished pump has improved this issue by about 90% or more. I have a sacrificial cover for the timing chain adjustment.

In the past after going for a ride, there would be no less than 6 to 8 oz’s of oil in the sump and more later as it drained from up top. After this ride today and after the changes, I drained off 2oz from the sump. I think I must contribute this improvement to the improved efficiency of the pump.

As far as the breather issue is concerned, the bike ran smooth as ever with no noticeable differences in performance. My contention is that lbs of pressure require the same energy to produce lbs of vacuum and that the best possible scenario is to minimize both. Yes, a one way valve of any kind on the breather will reduce oil leaks by decreasing HIGH pressure, but will not increase power by substituting pressure for vacuums.
What take more effort? Blowing up a balloon or the equivalent sucking a thick milkshake up a straw. The point is that it takes effort (HP) to produce both.
There is point in time during the stroke where no pressure or vacuum exists. The best way to produce and extend the duration of this condition is to allow air to move out AND in as easily as possible. This will also reduce high pressure yet increase efficiency by not trying to create an opposing force.
I am finding the duel breather on the 72’s to be quite promising.

The theory is that it takes less energy to spin the crank in a vacuum than in air, not only that, pumping air in and out of the engine takes energy too so the idea is to minimise pumping losses while provding a lower air density in which the crank will spin, that is why a one way valve is better than an open crankcase. A side benefit to having lower air pressure in the crankcase is fewer leaks.

Check out the other posts on this subject and read what Jim Comstock wrote about his experiments.

Jean

Yep in our 360 twins one way out free breathing should provide
1. less oil to no oil weeps
2. less density for pumping losses, ie: pushing-pulling air through small passages
3. less air-vapor density for less windage drag
4. more than one way to skin our breather venting cat, but good evacuation may need oil seals reversed to keep air out rather than oil in.
5. extra effective pump to low PSI can also suck oil mist to liquid oil right out too

more than one way to skin our breather venting cat, but good evacuation may need oil seals reversed to keep air out rather than oil in.

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No doubt. If oil leaks out under pressure, then air will certainly leak in with a vacuum.

The tighter the clearances in the oil pump wall and gears is what helps keep that oil from sumping.


Tyler

With exhaust eductor Hope to be able to let some filtered air in via Peel's head to flush corrosive gases out and maybe aid the extra oil flow out exhaust rockers to push-suck down the crack of the lifter pairs. Hope this constant search for prefect
Commando never ends.

I just went for another highway ride, 20 mile at 75 to 80mph hovering around 4500rpm. In conjuction with a fresh oil pump, the lubrication flow was great. The oil warmed up much sooner than usual, A good sign of flow. When stopping, shutting down and checking the oil, it's a 1/4 inch up the stick which I think is great and after letting it idle for a minute, it's right up to proper level. Again, when I drained the sump, I measured 50 ml. This is a good sign of scavenging, not usually found with 72's. When i looked in the tank while running the oil is running like crazy.
On the breather side, both seem to share the burden, huffing and puffing away with no noticable difference between the two except for I have no dripping of any kind from the timing breather. I find this to be quite favorable.
I feel assured knowing that the oil is finally coming and going as intended, without leaks, with out check valves or extensive teardowns and modifications.
I have heard from another who has done this on a 71 with the same results.
Any others brave enough to chime in?

motoalchemist said:

The tighter the clearances in the oil pump wall and gears is what helps keep that oil from sumping.


Tyler

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Absolutely, along with pushing it where it has to go and scavenging it up at a greater rate.

The losses in a crankcase have very little to do with the amount of air in the crankcase. You could have a crankcase that was sealed with a schrader valve installed and pump it up to 100 PSI pressure and another crankcase with a schrader valve and evacuated to 19 inches of vacuum. They would require nearly the same amount of power to turn. The only difference would be the air drag on the crank which at the speed a Norton crank turns would be nearly zero. Any work done compressing the air or crating a vacuum is regained when the piston changes direction.
Now if you leave the hole in the crankcase open air will be pushed out and drawn back in each revolution. This movement of air is work being done and it requires power. This is called pumping loss. Even this power loss is small enough that you would not feel the difference unless your seat of the pants dyno is a lot more sensitive than mine. Jim