Norton N15 oil tank vent pipe.

Andrew Jago · Feb 26, 2021

On top of my N15 oil tank there is a vent stub ( not the breather pipe that goes from the timed breather to the back of the oil tank ).
The parts book specifies an 18" hose for the vent - question is where is the hose supposed to go? Cant see any detail from the various photos and images I have, so any help would be much appreciated. Where did the factory put it?

ludwig · Feb 28, 2021

Because nobody else answers..
I forgot exactly how ( too long ago..), but It certainly wasn't connected to the air filter, or anything else.
It most likely just hang down, maybe to oil the rear tire ?

I vented it in a catch bottle, which itself is vented to a brazed-on tube on the chain guard, so that any oil is dumped on the lower run of the chain.
Something similar like on the later Commandos.
Every once in a while I unscrew the cap, and only a few cc water comes out. No oil.

texasSlick · Feb 28, 2021

An Atlas has a similar arrangement . The vent pipe goes to a stub on the upper run of the chain guard. Check your chain guard for a stub intended to receive your 18 inch tube.

However, This arrangement is not effective as a chain oiler. The speed of the chain creates a forward moving wind in the chain guard that deposits any oil in the vented air on the drive side crankcase. Ludwig's mod to terminate the tube on the lower side of the chain run may be better, but I suspect any oil is then deposited on the rear wheel rim. Either top or bottom, the chain moves too fast to be lubricated properly by a mist.

IMO, catch bottles catch very little oil, if any. The oil mist carries thru the bottle on the moving air, unless the bottle is fitted with scrubber media.

I have tried, perhaps a half dozen, different schemes to scrub the oil mist in the vent tube. None of these were very effective. I have succeeded in reducing the mist in the vented air to an insignificant level, by a mod internal to the oil tank.

The internal mod is described here: https://www.accessnorton.com/NortonCommando/atlas-dommie-oil-mist-scrubber.16411/#post-238783

I am not familiar with the N15 oil tank. I suppose one would have to weld in a short section of 1 inch tube if room is available, to simulate the Alas/Dommie tower.

Slick

ludwig · Feb 28, 2021

texasSlick said:
An Atlas has a similar arrangement . The vent pipe goes to a stub on the upper run of the chain guard. Check your chain guard for a stub intended to receive your 18 inch tube.

The internal mod is described here: https://www.accessnorton.com/NortonCommando/atlas-dommie-oil-mist-scrubber.16411/#post-238783

I am not familiar with the N15 oil tank. I suppose one would have to weld in a short section of 1 inch tube if room is available, to simulate the Alas/Dommie tower.

Slick

I don't think the N15 chain guard has that stub. At least mine didn't.
I also modified the ventilation of the oil tank. No oil is coming out, unless if I would really overfill it.

ludwig · Mar 1, 2021

This is a pic. of an oil tank I will probably use next season:

( still needs brazing and welding)
Vent stubs in and out are moved to the back to create more space for a toolbox.
The exit stub is extended in the tank away from the inlet.
But I believe the main reason there is hardly any oil mist escaping from the tank is the reed valve:

I tested it with a tube from vent stub in a glass of water, and only for a few sec. after start-up, I see air bubbles.
After that, almost nothing.
Too much ( contaminated) air coming out of the oil tank would be an indication of worn piston rings or leaking head gasket.
I don't know how effective the timed disk on the camshaft is.

Bernhard · Mar 3, 2021

texasSlick said:
An Atlas has a similar arrangement . The vent pipe goes to a stub on the upper run of the chain guard. Check your chain guard for a stub intended to receive your 18 inch tube.

However, This arrangement is not effective as a chain oiler. The speed of the chain creates a forward moving wind in the chain guard that deposits any oil in the vented air on the drive side crankcase. Ludwig's mod to terminate the tube on the lower side of the chain run may be better, but I suspect any oil is then deposited on the rear wheel rim. Either top or bottom, the chain moves too fast to be lubricated properly by a mist.

IMO, catch bottles catch very little oil, if any. The oil mist carries thru the bottle on the moving air, unless the bottle is fitted with scrubber media.

I have tried, perhaps a half dozen, different schemes to scrub the oil mist in the vent tube. None of these were very effective. I have succeeded in reducing the mist in the vented air to an insignificant level, by a mod internal to the oil tank.

The internal mod is described here: https://www.accessnorton.com/NortonCommando/atlas-dommie-oil-mist-scrubber.16411/#post-238783

I am not familiar with the N15 oil tank. I suppose one would have to weld in a short section of 1 inch tube if room is available, to simulate the Alas/Dommie tower.

Slick

Atlas has a vent tower on the top of the oil tank which takes the pipe from the side of the camshaft. Another pipe exits from this froth tower which connects to a short pipe on the top of the chainguard, supposedly to oil the rear chain, at least that was the thinking of Norton on the featherbed.

Andrew Jago · Mar 4, 2021

Thanks everyone - I think I will just route it downwards to exit adjacent to the oil feed/return pipes. 18” won’t do that though, it’s too short which made me think it went elsewhere, it will be more like 24”

texasSlick · Mar 4, 2021

Andrew Jago said:
Thanks everyone - I think I will just route it downwards to exit adjacent to the oil feed/return pipes. 18” won’t do that though, it’s too short which made me think it went elsewhere, it will be more like 24”

Keep your eye out for oil mist deposit. Terminate the tube where most convenient to mop up oil.

Slick

Norton N15 oil tank vent pipe.

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