Breathers

mdt-son said:

We are not talking of mass transport here. The breather must account for the time delay of approx. 60 microseconds for the pressure vawe to hit it. The pressure wave has the length of a quarter of a crankshaft rotation cycle (90 degrees). At 6000 rpm it is exactly 2.5 microseconds long, which compares well to the cycle time of the camshaft and breather (20 microseconds).

Click to expand...

I think we are talking about mass transport rather than pressure waves (positive or negative).

I doubt that the mass of air pushed down by the pistons is going to reach and pass through the open timed breather valve within a timescale of a few microseconds.

At some rpm ranges, the valve may be closing at exactly the wrong time.

I confess that coming from a background of primarily Japanese engines from the late 1960's to the late 1990's, I find all the effort that goes into Norton crankcase breathers (and other british and american engines) a bit confusing. On most Japanese engines the breather is little more than a hole in the crankcase. Okay, so in some cases there may be a little bit of baffling to keep straight oil from just glooping out all over everything, but most certainly do not have any sort of timing mechanism. On earlier engines there is a hose that vents to atmosphere, later they ran a hose from the breather to the airbox, just upstream of the carburetor(s). And the only trouble I have ever had from any of them is when the breather hose has been blocked for some reason.

In the case of a 4 cylinder (2 up, 2 down) or a 180 degree twin (1 up, 1 down), I could see the argument being made that the pressure in the crankcase should remain more or less constant (even though I know it doesn't), but the old KZ750 twin is a both up, both down engine and it doesn't have any sort of timed breather. IIRC, neither do any of the old Honda 350 or 360 twins.

Is it all simply to do with relative crankcase volumes? Obviously pre-unit engines have relatively small crankcases, while unit constructed engines, (in which the crankcase and the transmission share a common oil sump), have a lot more crankcase volume, especially on older examples of the type.

Still, though--imagine a man were lunatic enough to just run say a 3/4" hose from somewhere up high on his Norton crankcase directly to the top of the oil tank, (making sure of course that the oil tank was in turn properly vented). No valves, no restrictions. What would happen to that poor fool?

A big hose works well as a breather.

BSA/Triumph ended up using one on singles and twins, as did Enfield.

Timed breathers seemed like a good idea in the 1930s and oil leaks could just be blamed on the customer for “thrashing the bike,” anyway.

Triton Thrasher said:

I think we are talking about mass transport rather than pressure waves (positive or negative).

I doubt that the mass of air pushed down by the pistons is going to reach and pass through the open timed breather valve within a timescale of a few microseconds.

Click to expand...

Once the crankcase has been evacuated, the only mass that needs shifting is the blow-by gas, which shouldn't be a large quantity if the engine is in good nick. When a clear hose is attached to the timed vent or a reed valve, the aerated oil moves very slowly, from what I've been told.
I have yet to experiment with this myself. To me the slow movement indicates a very low mass transport. I doubt even a worn running engine will produce much gas mass to justify the claim of a timed breather shifting significant volumes of mass.

I think there might be an error in your thinking. If the valve had to expel the gas mass of swept volume for every crank rotation, that mass would have to be replaced continuosly - from where? Not from blow-by gases, and not from the top end, so where is the source?

- Knut

Triton Thrasher said:

I think we are talking about mass transport rather than pressure waves (positive or negative).

I doubt that the mass of air pushed down by the pistons is going to reach and pass through the open timed breather valve within a timescale of a few microseconds.

At some rpm ranges, the valve may be closing at exactly the wrong time.

Click to expand...

I agree. Which I why I prefer a reed valve. A reed valve is ALWAYS timed perfectly !

Triton Thrasher said:

A big hose works well as a breather.

BSA/Triumph ended up using one on singles and twins, as did Enfield.

Timed breathers seemed like a good idea in the 1930s and oil leaks could just be blamed on the customer for “thrashing the bike,” anyway.

Click to expand...

Not true. A65 engines have a timed breather as well at the end of the camshaft, p/n 68-0131. Late B50 engines have a scavenge valve fitted, part no. 71-2771.

- Knut

Triton Thrasher said:

I think we are talking about mass transport rather than pressure waves (positive or negative).

I doubt that the mass of air pushed down by the pistons is going to reach and pass through the open timed breather valve within a timescale of a few microseconds.

At some rpm ranges, the valve may be closing at exactly the wrong time.

Click to expand...

Notes from an under thinker:

The timed breather is a constant being driven by the cam. For it to do anything at the wrong time (whatever that means to you guys) the cam would have to stop spinning, would it not? The disc arrangement still opens and closes at the same degrees in the stroke regardless of RPM. Whether or not it is doing much or needs to do much at 6-7000RPM is not something I worry about enough to try and figure out.

I've not used the timed breather alone at 7000 RPM. I have used the cNw breather at 7000 RPM and the motor did not feel like it was hitting a wall when I shifted into 4th at 85mph. I only shifted because I wasn't sure if the motor would blow to pieces if I didn't. Whatever the case, my engine is breathing like it should for my use.

Carry on with the closet science.

Fast Eddie said:

I agree. Which I why I prefer a reed valve. A reed valve is ALWAYS timed perfectly !

Click to expand...

Yes the reed valve does, but you are underestimating the engineers. Fitting a timed breather working in a certain rev range only would be pretty daft. That's why the rotary valve has a slot.
Commando engines is a different animal though, as NV in their infinite wisdom deleted the timed breather for MY 1972 onwards.

- Knut

Junglebiker said:

Still, though--imagine a man were lunatic enough to just run say a 3/4" hose from somewhere up high on his Norton crankcase directly to the top of the oil tank, (making sure of course that the oil tank was in turn properly vented). No valves, no restrictions. What would happen to that poor fool?

Click to expand...

Nothing probably, except increased pumping losses and some noise from air being pushed back and forth. And oil leaks from the engine of course.

- Knut

I've had an Atlas, an N15 and a Commando all with the timed breather. I've never had leaks from any of the engines. Perhaps it's the Wellseal.

Junglebiker said:

Still, though--imagine a man were lunatic enough to just run say a 3/4" hose from somewhere up high on his Norton crankcase directly to the top of the oil tank, (making sure of course that the oil tank was in turn properly vented). No valves, no restrictions. What would happen to that poor fool?

Click to expand...

Ron Wood had some big hoses coming off various places on the flat track bike. I don't know where they went though. Back then the oil spittle could have gone down on the track.

It would work, but might not be as quit as smooth running at lower RPM without some kind of device to prevent the upstroke from sucking air back into the crank case, which could keep the crankcase pressure a little high until RPMs increased. Not positive about that though. I did it long ago with two 1/2" hoses coming off the back of the timing chest. They were T'd together and a big Ford PCV valve used before going into the oil tank. The idea with the PCV valve was to reduce air from getting sucked back into the crankcase. I don't think it did a very good job, but the motor ran well. The oil tank vent went into a Yellow Play-Doh canister tucked in the triangle below where the coils mount on a P11. I had to do it because the 2S cam I used did not support a timed breather. That and the Jim's weren't selling finished parts at the time. Somebody was selling a huge breather gizmo that could be put on the back of the timing chest. It looked like a galvanized steel grain silo. Old Brits was around and had notes on using brake booster check valves and such. Anyway, my memory is not that great for all of what was available, but it was not much.

If you busted the stationary breather disc out of your P11 timed breather that JSM reed valve should be sufficient to do the work the timed breather would do. No guarantee of course.

Also what mdt-son said. Gurgling and without a catch can oil mist and froth would come out of the oil tank vent hose.

mdt-son said:

Not true. A65 engines have a timed breather as well at the end of the camshaft, p/n 68-0131. Late B50 engines have a scavenge valve fitted, part no. 71-2771.

- Knut

Click to expand...

Thanks. I need assistance from the knowledgable !

Fast Eddie said:

I agree. Which I why I prefer a reed valve. A reed valve is ALWAYS timed perfectly

Click to expand...

Fast Eddie said:

I agree. Which I why I prefer a reed valve. A reed valve is ALWAYS timed perfectly !

Click to expand...

If there’s a positive pressure in the case, a reed will relieve it. If there’s negative pressure, a reed will hold it.

Simples!

Schwany said:

Parts is parts: The timed breather in a P11, Ranger, N15, or Atlas has 4 three primary parts. A camshaft machined to support a timed breather, a stationary breather plate, a rotary breather plate (the disc), and a spring. Look at parts 81, 82, 83, and 84 in this exploded view. The above-mentioned breather parts are all used on my engine, except my cam is a JS2SS, not a stock cam. Only brought this up because Thomasa said no spring. Does that make me a bad person? lol

Click to expand...

I may have confused the issue. No spring referred to the "check valve" in the crank boss of a G80 Matchless engine. No rotary motion at all. It appears that the disc, sucked (no spring) fitting tightly against the base of the fitting on the upstroke, is intended to prevent air from returning into the crankcase (which in this case includes the primary chaincase as there is no crank seal) and the disc is blown open on the down stroke.

In all these situations ( timed Atlas, Dommie etc. or late commando with reed valve added) once the engine crankcase is evacuated during the first few crank rotations, there is very little air movement through the breather system as there is a vacuum in the crank case. Only blow-by will need to be evacuated on a continuing basis. Measurements posted showing ~18 inches of vacuum bear this out.

FWIW, GM had rear main bearing seal leaking problems for years with the rope-style seal, particularly on truck sixes in heavy service. In the late fifties they added a PCV system that, while not creating a vacuum, reduced the crankcase pressure considerably compared to the previous road-draft tube. Those engines leak a lot less oil. I have two of them one with road draft and one with PCV.

Speaking of the timed breathers, my first Commando was a '71 PR that had the early design breather at the end of the camshaft. I never had any trouble with it, but after I had raced it for while, and went to C.R. Axtell for some engine work (and lots of really great advice), he mentioned that they didn't like to use the hollow camshafts from the timed breather engines as regrind cores, because they sometimes broke. I gave him a couple of solid cams to use for my regrinds, and blocked off the breather port with a short bolt, as well as fitting a breather tube to the back of timing side, as in the later engines. The vent from the oil tank was routed to a catch bottle, but as long as the engines were fairly fresh, I didn't get much in the bottle. I never really had any breather-related issues with the stock Commando systems, although I did see more blow-by when I was first working with the 920 big bore conversions, before I got the ring seal problems sorted. On the other hand, I have a Comstock sump plug breather on my grandson's 883 Commando, and really like how well it works.

Just another little tidbit of old guy experience, for whatever it's worth.

Ken

The pic below shows what my vent tube out of the oil tank goes into. Obviously, my Norton is not a restoration. The tube from the oil tank goes into that little air compressor water filter catch can in front of the shock. You can't see the vent tube from the oil tank in this pic. As long as the catch can does not fill to the top no froth gets to the conical filter at the end of the run, only air gets through. The catch can has always gotten some froth in it even day one after a fresh rebuild. It gets a lot less froth in it if I short shift and ride at the speed limit on city streets. Once I get over 60mph in 3rd, or cruise at HWY speeds, which around here are 70mph in 4th it starts to get some noticeable froth in it. The froth in the catch can in the pic is from 12 miles of riding, 1 mile of it at 90mph in 4th. When on longer spirited rides the catch can fills up over 1/2 way to the sintered filter and starts to gurgle. I have to empty it after 200 to 300 miles depending on how childlike I ride. The sintered filter in the catch can has 8 holes drilled in it to keep the air flowing out.



All my crank revolutions must be the first few. Otherwise, that canister would be empty, right?

One of the engineers here want to tell me what impending doom awaits because that froth is in my catch can, and not in my oil tank?

Do Commandos have froth towers on the oil tank, or does that froth get recirculated in the oil? Or are Commandos immune to creating froth?

Not a Norton, but the manual for my roller bearing crank Suzuki 1100E says it should be between 1.4 and 7.1 psi at 3k rpm. It's happy with low oil pressure. The 750 which is same architecture but plain bearings is 43 -78 psi at that RPM. With the Norton being plain bearing, wouldn't a wide open 3/4 hose give too little pressure? I'm not a tuner just trying to learn.

I have a breather now, but I'm going to route back into the air cleaner, it lightly mists the engine when I cane it, which is 10K RPM runs putting down 185 RWHP. So it's understandable, yet annoying. Is there any problem with just doing this? It's how my car's set up.

gpzkat said:

Not a Norton, but the manual for my roller bearing crank Suzuki 1100E says it should be between 1.4 and 7.1 psi at 3k rpm. It's happy with low oil pressure. The 750 which is same architecture but plain bearings is 43 -78 psi at that RPM. With the Norton being plain bearing, wouldn't a wide open 3/4 hose give too little pressure? I'm not a tuner just trying to learn.

I have a breather now, but I'm going to route back into the air cleaner, it lightly mists the engine when I cane it, which is 10K RPM runs putting down 185 RWHP. So it's understandable, yet annoying. Is there any problem with just doing this? It's how my car's set up.

Click to expand...

Oil pressure to the big ends is not air pressure in the crankcase.

gpzkat said:

Not a Norton, but the manual for my roller bearing crank Suzuki 1100E says it should be between 1.4 and 7.1 psi at 3k rpm. It's happy with low oil pressure. The 750 which is same architecture but plain bearings is 43 -78 psi at that RPM. With the Norton being plain bearing, wouldn't a wide open 3/4 hose give too little pressure? I'm not a tuner just trying to learn.

I have a breather now, but I'm going to route back into the air cleaner, it lightly mists the engine when I cane it, which is 10K RPM runs putting down 185 RWHP. So it's understandable, yet annoying. Is there any problem with just doing this? It's how my car's set up.

Click to expand...

I think there is some confusion on my part.

If talking about crankcase breather plumbing (what this thread is supposed to be about), a 3/4" hose would be moving air and relieving crankcase pressure. The air pressure going through the hose would not be an issue and would have no affect at all on bearing lubrication.

A 3/4" oil feed hose from the oil tank to the oil pump would require different fittings in my case. Same with the return. Not sure what it would do to the return oil pressure. It might slow down a little, but it is not a high pressure line. Oil pressure in the engine feeding the bearings would not be affected by a 3/4" oil feed or oil return hose. I wouldn't do it because of the fittings all being wrong for 3/4"

Regarding moving the breather hose back to the air cleaner. I think that is how Suzuki did it on later models with big air boxes. If after rerouting the breather to the air cleaner, the engine starts misfiring due to plug fouling from one type or another contaminate, I'd say it's not working without a catch can before the air cleaner, otherwise go for it.

Not sure if I'm helping or confusing, or even relevant.

Triton Thrasher said:

Oil pressure to the big ends is not air pressure in the crankcase.

Click to expand...

Yeah just another senior moment.