S/central oil tank versions

These are the two versions of the "S" /central oil tanks I am in possession of.
I will admit that I no longer remember the VIN of my original 70 canary yellow roadster.
I also don't know which oil tank it had. Only anecdotally I heard at high speed it would suck out the oil of the cam end timed breather and pass it through the engine and out the tail pipe. I now wonder if the long interstate runs followed by the 115mph (indicated?) run caused the final blow-up while going home to Great Bend NY.
What was the reason for the vent revision and which one would you suggest I use on my next 70 build?
Vent in the dome vs Vent to the side of the dome.
The dome stays as the origin of the internal air cleaner vent tube.
TIA

Hi Dave
I’m not doing anything...and it’s raining.
On the left is from a Dec1969 build with a previous owner added vent. On the right is from my Mar1969 750S project. Both are the same.

Also the one on the left with added vent has the air cleaner vent hole, on the AC back plate, welded shut.

Thanks I'm guessing the RH one shows a lot more brazing and hand work and may have been an early one. I don't think it would be a "we need one or two to close this model/variety out" and move on to the 71's. What is the oil level mark distance for these 06-1338 caps?
TIA

hey Dave, I have a 70 with the "camshaft breather hose port inlet" on the body of the tank next to the dome. (not on the dome itself) the tank on the right in your pictures

As I recall, the straw for the "oil tank breather" for the oil tank extends up into the dome as a precaution for it to suck more air and less oil if it's splashing about in the tank. IF the "camshaft breather tube inlet port" also enters the tank on the dome, then any oil that was ejected out of the camshaft port would enter the oil tank in close proximity to the oil tank breather straw which is positioned where it is precisely to avoid picking up oil. I can't see how having the camshaft breather hose port enter on the dome is a better position if the oil tank breather straw is also terminating inside the dome...

Maybe the oil tank breather straw doesn't terminate in the dome on the oil tank on the left, then the camshaft breather inlet port wouldn't dump oil on tank breather straw...

At one point I was very curious as to how much oil was ejected out my timed breather port, so I mounted this translucent high temperature tubing (from mcmaster) in place of the camshaft breather hose because I wanted to see if there was a flow of oil and exactly what sort of amount might it be. With the engine started, there was a continuous march of bubbles up the hose which thinned and popped as they proceeded up the tube. When I held the RPM's up the bubble marched up into the oil tank. When I shut the bike off, all the bubbles popped and drained down to the timed port. If the engine happened to stop in a position where the port was closed, there was about 5" of oil in the lower part of the tube. If you rolled the engine over, that 5" of oil would drain back through the port when it aligned in the open position.

Sorry for the thesis posted above, I always appreciate your input, so I was trying to be thorough.

I've got the same 2 oil tanks. The one with the port in the 'top hat' is off my APR 1969 production date. The other one is from an unknown issue I picked up somewhere. Pretty sure on both of them, that hole in the front of the tank (inside the air filter) is a pipe that runs back and bends straight up into that 'top hat' and ends open there. The port in the top hat or on the top of the tank is from the timed breather, and is a return from the engine. I look at it as sort of an oil/vapor separator/oil tank breather. I got tired of the oil vapor condensing (or I filled the tank too much not knowing early on) and oil would come out that hole in the front and get all over the bottom of the trans. When I rebuilt it, I threaded that hole in the front and put a 'nipple' in it and attached a hose that ran out the chrome cover plate and into a catch bottle. It sure keeps the oil off the trans. Makes for a process getting the air filter off, but then I always seem to take the carbs off to do that anyhow.

I think the best thing is to re-plumb the early bikes for a better breather and get rid of that timed breather off the LS which is ineffective at best and just block most of those ports. But the tank has to be open to the air somehow.

I have a pic of the oil tank cap/level indicator if you need, next to a ruler.

I concur with oOnortonOo that the breather port is better positioned away from the dome.
The breather in dome is similar to the arrangement on an Atlas oil tank, where the engine breather port enters the dome (or tower) at the tower base, turns 90 degrees downward, and the tank breather comes off the top of the tower.

I found oil was carried over from the engine breather to the tank breather, and ended up on my rear wheel, the tank breather being plumbed to the rear chain guard. I greatly mitigated the oil carry over by first using a catch bottle filled with scrubber media, then by building a scrubber into the oil tank tower itself. https://www.accessnorton.com/NortonCommando/atlas-dommie-oil-mist-scrubber.16411/

Based on my experience, I would keep the engine breather port away from the dome.

Slick

DogT said:

View attachment 15150

Click to expand...

My two are the same as yours.

Dog T thanks on the cap/stick 3" measurement pix
I've got 2-1/4" (4), 2-1/2" (1), and 2-3/4" (5: 1 being from my 5 mile MKIII)
I've got a fair amount of tanks, 1 fastback, 2 "S", and the remainder are roadster at least a dozen.
Will have to keep an eye out for a 3"cap

o0norton0o said:

snip
At one point I was very curious as to how much oil was ejected out my timed breather port, so I mounted this translucent high temperature tubing (from mcmaster) in place of the camshaft breather hose because I wanted to see if there was a flow of oil and exactly what sort of amount might it be. With the engine started, there was a continuous march of bubbles up the hose which thinned and popped as they proceeded up the tube. When I held the RPM's up the bubble marched up into the oil tank. When I shut the bike off, all the bubbles popped and drained down to the timed port. If the engine happened to stop in a position where the port was closed, there was about 5" of oil in the lower part of the tube. If you rolled the engine over, that 5" of oil would drain back through the port when it aligned in the open position.

Sorry for the thesis posted above, I always appreciate your input, so I was trying to be thorough.

Click to expand...

Frank
Appreciate the clear tube experiment share here. Shows the volume of oil involved. Makes the separated engine breather sound a bit better. But having seen what puffing air can do to liquids dispersal, A focused experiment/modification may be needed on an "S" tanks to get it right...
I have a cut open skeleton roadster tank. The internal roadster baffles are more sophisticated and are maybe under appreciated...