Breathers

gpzkat said:

Yeah just another senior moment.

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Just to be clear, my hypothetical 3/4" hose was intended as a crankcase air pressure breather, not an oil line. In my hypothetical situation, I ran the 3/4" hose back to the oil tank because that is where the stock crankcase breather runs to--the top of the oil tank, the idea being that any oil which finds its way out the crankcase breather and through the breather hose will end up back in the oil tank.

The primary purpose of the hypothetical 3/4" hose in my hypothetical engine was to keep crankcase pressure to a minimum. I was hoping to draw out anybody who would might have a strong opinion as to why such a crankcase breather would be a bad idea.

Junglebiker said:

Just to be clear, my hypothetical 3/4" hose was intended as a crankcase air pressure breather, not an oil line.

The primary purpose of the hypothetical 3/4" hose in my hypothetical engine was to keep crankcase pressure to a minimum. I was hoping to draw out anybody who would might have a strong opinion as to why such a crankcase breather would be a bad idea.

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After the first few revolutions of the engine after start-up, the mass of gas pumped out the breather decreases to the extent a 3/8 or 1/2 inch diameter hose is entirely adequate. Thus a 3/4" hose is unnecessary and moreover ugly.

Keeping sump pressure to a minimum, is the function of the reed valve, or timed disk to prevent leak back.

Slick

Junglebiker said:

Just to be clear, my hypothetical 3/4" hose was intended as a crankcase air pressure breather, not an oil line. In my hypothetical situation, I ran the 3/4" hose back to the oil tank because that is where the stock crankcase breather runs to--the top of the oil tank, the idea being that any oil which finds its way out the crankcase breather and through the breather hose will end up back in the oil tank.

The primary purpose of the hypothetical 3/4" hose in my hypothetical engine was to keep crankcase pressure to a minimum. I was hoping to draw out anybody who would might have a strong opinion as to why such a crankcase breather would be a bad idea.

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Not bad, just big. It would work like you think it does. No big deal if installed with a reed valve high in the crankcase. It might not blow that much oil into the oil tank at that diameter unless hooked up to a sump plug breather and the sump was filled with oil on cold startup.

Schwany said:

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?

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The Commandos did not have any serious sort of air-oil separator in the oil tank, just a bit of baffle at the vent pipe to keep from pumping oil out the vent tube. The tank vent was open to the atmosphere. For the MK3, they changed the vent by using manifold vacuum to pull the air out the vent tube, and added a small "air-oil separator" in line, with a feed to the air cleaner.

This is the 1972 system, taken from the parts manual. The breather hose (2) connects to the the timed breather at the end of the cam.



This is the later 750 and 850 system, with the breather connected to the back of the timing cover and the addition of an oil filter.



And this is the MK3 system, with the air-oil separator (34) and the deletion of the chain oiler.



The earlier 1968 style Commando oil systems is different, with a different tank design. I don't have any good pictures of it handy at the moment.

Ken

Schwany said:

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.

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There are two flows coming from the crankcase: one is the return-oil from the sump and the other is the blow-by venting from the crank case. Of course air and oil get mixed in both flows, less so as the engine develops a vacuum in the crankcase (assuming a check valve of some sort) and need to be separated.

Is the froth that gets caught in your water trap coming from the crank case breather directly or from the oil tank? Bear in mind that at high RPM the return pump can starve as oil gets flung against the walls of the c'case. Norton dealt with this by moving the return pickup on some engines (combat?) but I don't know if they had addressed that issue in the P11 era. I suspect not. Perhaps someone more knowledgeable than I can address this issue. But it seems possible that at least some of the oil that ends up in your froth catcher should have been picked up by the scavenge pump and returned to the tank. That probably happens only at very high RPM where oil goes out the breather rather than back to the pump. As I said, perhaps the racers can tell us about that.

Ideally the volatiles in the hot oil should to be condensed back into the oil else the viscosity creeps up over time. Hopefully that's what happens in the froth tower of the oil tank but I've found it marginally effective on my G80 Matchless and the G15 I had, both of which had very similar oil tanks. Condensing the vapors isn't so much an issue in race engines but is for longer term maintenance intervals.

The old GM road-draft tube had a condensing tower to drain the condensed vapor back into the sump while the air drawn in at the filler pipe circulated on out the draft tube. The little holes in the tower did plug up and then they just blew oil out the road-draft breather when the oil got hot. When working hard in hot weather those engines would see oil temperature of 250F and up. In those days they had no oil coolers on the medium duty trucks.

By the MKIII era Norton just burned the separated oil without returning it to the tank. It can coat the backs of the intake valves with coke and in some engines begins to obstruct the incoming air flow. This was especially a problem when combined with low quality gasoline in the early 80s. BMW cars had a service bulletin to remove the intake manifold and blast the backs of the valves with crushed walnut shells. Leaking stem seals can cause a similar problem as can excess oliphens (wax) in the gasoline.

lcrken said:

This is the 1972 system, taken from the parts manual. The breather hose (2) connects to the the timed breather at the end of the cam

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That's the pre-'1972' (pre-200000) camshaft timed breather (the diagram is from the '1971' parts manual).

lcrken said:

This is the later 750 and 850 system, with the breather connected to the back of the timing cover and the addition of an oil filter.

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The '1972' (200000+) and '1973' (220, 230, 235 series) 750 models all had the same rear crankcase breather except for some late '230' series 750s that had 850 crankcases so the '850' timing case breather.

Thomasa said:

Is the froth that gets caught in your water trap coming from the crank case breather directly or from the oil tank? Bear in mind that at high RPM the return pump can starve as oil gets flung against the walls of the c'case. Norton dealt with this by moving the return pickup on some engines (combat?) but I don't know if they had addressed that issue in the P11 era. I suspect not. Perhaps someone more knowledgeable than I can address this issue. But it seems possible that at least some of the oil that ends up in your froth catcher should have been picked up by the scavenge pump and returned to the tank. That probably happens only at very high RPM where oil goes out the breather rather than back to the pump. As I said, perhaps the racers can tell us about that.

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The froth is going into the catch can from the froth tower vent tube. The froth tower is fed directly by the breather plumbing. The froth tower is the size of a film canister with the breather hose going in low and vent hose coming off higher on the tower on the opposite side. If any hot oil accumulates in the froth tower it dribbles down into the main oil in the tank. I don't get oil in the catch can currently with both breathers plumbed into the froth tower, only froth that refuses to turn back into oil and a little bit of water.

If I'm not mistaken the straight up motor in a P11 is less susceptible to oil starvation than early Commandos. The level oil well in the sump stays much closer to filled under acceleration and keeps more oil around the return pickup than the early canted forward motor did. I have pushed the motor as hard as the little thing will go within reason (7000RPM). If the engine was starving for oil under hard acceleration, it would have blown up by now. As a matter of fact, tomorrow I'm changing the gearbox sprocket to a 20 from a 19, so I don't beat on it so much.

I'll have to check the return oil going into the tank after I get back from a ride and see what it looks like. I think it may have small high end champagne sized bubbles in it. Never bothered to look in the tank with the motor running after a ride. I've only looked in there after a cold start. Maybe I'm pumping nothing but 20-50wt froth when the motor is fully warmed up. Must be good froth though.

L.A.B. said:

That's the pre-'1972' (pre-200000) camshaft timed breather (the diagram is from the '1971' parts manual).

Andover Norton Parts Drawings - Genuine Andover Norton Factory Parts - Commando Parts

Andover Norton Parts are the only Norton spare parts in the market manufactured to original drawings, within the factory-approved tolerances, from the correct materials, and with the correct finish.

andover-norton.co.uk

The '1972' (200000+) and '1973' (220, 230, 235 series) 750 models all had the same rear crankcase breather except for some late '230' series 750s that had 850 crankcases so the '850' timing case breather.

Andover Norton Parts Drawings - Genuine Andover Norton Factory Parts - Commando Parts

Andover Norton Parts are the only Norton spare parts in the market manufactured to original drawings, within the factory-approved tolerances, from the correct materials, and with the correct finish.

andover-norton.co.uk

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My mistake on the early diagram. It is from the "1971" parts manual from Kim's Norton CD, with this cover.



FWIW, the second diagram is from the parts manual with the following cover. In line with what LAB said, a version of the 750 parts book published in1972 also shows the same diagram.



And the final diagram is from this parts manual.



Ken

Use the timed breather OR the reed breather.

If you install my reed breather then you need to plug the existing breather. Cam or otherwise.
Leaving both connected kills the resonance that the reed needs to operate efficiently. Jim

gortnipper said:

Use the timed breather OR the reed breather.

If you install my reed breather then you need to plug the existing breather. Cam or otherwise.
Leaving both connected kills the resonance that the reed needs to operate efficiently. Jim

'70 camshaft breather not working - tach drive leaking? (2014)

Your conclusions make sense to me. I think I will proceed with adding the Comstock sump breather sold by NYCNorton, and leave the timed disc breather in place and see if that solves my tach leak problem. If you install my reed breather then you need to plug the existing breather. Cam or...

www.accessnorton.com

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I stated it is recommended to block off the timed breather when installing a reed breather at the start of this thread. That is how I ran the fresh motor initially.

My motor works fine with both connected and it is easier to kick over. If the reed valve is not doing an optimal job anymore, it doesn't matter to me. The addition of the timed breather being plumbed in is doing a better job than the reed breather alone. No oil leaks, which was my goal. I have no plans to disconnect the timed breather or the cNw reed breather regardless of the expert advice until something negative happens. So far zero evidence of that. Time will tell.

Congrats! You've built a breather with a vacuum secondary! Only opens when it's needed.

Junglebiker said:

Congrats! You've built a breather with a vacuum secondary! Only opens when it's needed.

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I have no idea what I have built, but it is not as slow as a stock 750 Norton.

I don't recommend anyone do what I do to their precious Nortons. I do what I do, and it usually works, or I figure out how to make it work. I know you understand coloring outside the lines.

I probably should not have posted anything about breathers in the first place though. The breather horse has been whipped to mush on this site.

Junglebiker said:

Congrats! You've built a breather with a vacuum secondary! Only opens when it's needed.

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Not a vaccum - a partial vacuum, at best.
If you look at #20 you will notice the pressure drop is 45 mbar only, while ambient pressure is 1013.25 mbar on average across the world, at sea level.
So, the internal pressure is quite high, but sufficiently low to keep the engine oil tight under normal operation.

A question of semantics; Does the "high" internal pressure of 96,800 Pascal (968 mbar) correspond to a "high" or "low" partial vacuum?

Maybe I meant "relative" vacuum. For if the pressure outside is lower than the pressure inside, than the pressure outside must--relatively speaking--be a vacuum, no?

If the pressure outside was never lower than the pressure inside, then no reed valve breather would ever open.

Went for a 200 mile ride Thursday and only had 1/4" of froth in the catch can when I returned. When using only the reed breather it would be 3/4 full on that same ride. My guess is the reed breather is not doing much anymore due to the resonance issue Jim Schmidt mentioned. Might be the negative thing I was waiting on to switch things back. lol