CNW Breather issues

If breather was bad I'd think that oil would be coming from every orifice. Had guy plug breather hose from tank and oil came from everywhere. Those Reed breathers are bullet proof and would be last thing I'd check. Rings and oil return from heads may be the culprit. If it has scrolled rocker shaft maybe they were installed wrong causing over oiling of head.

Beach said:

If breather was bad I'd think that oil would be coming from every orifice. Had guy plug breather hose from tank and oil came from everywhere. Those Reed breathers are bullet proof and would be last thing I'd check. Rings and oil return from heads may be the culprit. If it has scrolled rocker shaft maybe they were installed wrong causing over oiling of head.

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Agreed, but it begs the question - why did the problem disappear when the breather was removed ? I would defo check that the petals are free to move.

cliffa said:

Agreed, but it begs the question - why did the problem disappear when the breather was removed ? I would defo check that the petals are free to move.

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Who knows. Sounds like old school guy already made his determination. Plus op mentioned factory breather is temporarily installed(how do you do that?). Owner needs to check himself. Not sure he even has bike back yet. That breather is pretty simple. Hope he figures it out soon.

coomo said:

...Engine was completed by the most well known ex factory Norton racer/designer in UK...

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Did he go back to the Cam breather, or the Timing side breather?

cliffa said:

Agreed, but it begs the question - why did the problem disappear when the breather was removed ? I would defo check that the petals are free to move.

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Perhaps because the plumbing was changed at the same time. Sounds like thats also when the catch tank was added to the tank vent. Presumably before that it went to the air filter?

Either that or the breather unit was somehow incorrectly assembled?

There are lots of holes in the logic so far and it would be good to know the details and get to the bottom of it. Sadly however, stories like this usually get left hanging.

But (I was being too polite before I think so I’ll state it here clearly): my overriding point is that the cNw breather unit, assembled correctly and fitted correctly, cannot possibly cause engine smoking. Period.

Further to your point @Fast Eddie, if the vent was spraying oil into the filter - could explain smoking?

robs ss said:

Further to your point @Fast Eddie, if the vent was spraying oil into the filter - could explain smoking?

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That would be my hypothesis.

We are not mentioning who built the engine?
But by the description, it sounds like Norman White?

He mentions in his excellent book/17 chapters of Andover Norton advertorial that Edward Turner designed the Norton twin.

Norman is very traditional in his approach to engine building, and I wouldn’t be surprised if he sees a reed breather solution like the cNw crankcase mounted unit as new-fangled and not necessary.

I see in the book that Norman blocks up the breather on a Combat crankcase – drilling holes into the timing side, as per the original factory notes.

So, I do wonder if this is the reason for going straight back to the factory standard breather on the OPs bike - maybe Norman doesn't subscribe to the benefits of displacing air from the descending pistons via the best possible route, nor the benefits of negative crankcase pressure helping to keep the bike oiltight as the pistons go back up?

For the OP's 1970 bike, breathing would surely be via the rather poor timed breather off the end of the cam?
I wonder how this was dealt with as part of the rebuild?
If the cNw breather was being fitted, then I would have blocked up the hole in the crankcase at the end of the cam, and removed the "rotary breather plate" and it's accompanying spring.

As Nigel says, threads like this usually fade away into the abyss leaving lots unanswered, which is a huge shame, as this is a very interesting topic, and I'd love to know more!

Yes it is Norman.I visited yesterday.On removing the CNW breather and running the pipe into a bottle,a far bit of oil vented.We couldnt road test,as its pissing down.
Now ill explain the complete set up guys.Its a 70 bike with the central oil tank.The CNW breather returns to the spigot on the filler neck.(the same place as original vent)Its a crush proof line with a direct route.
The original tank breather,is basically a hole with vents into the air filter pod.As I used a mikuni, I made a spigot, and then ran a hose to a small catch tank.
Yesterday, I attempted to blow air through the catch tank(lung version) I did so, but it wasnt that easy.Awaiting updates.I will bring this thread to a conclusion and hopefully an answer as it progresses.

coomo said:

Yes it is Norman.I visited yesterday.On removing the CNW breather and running the pipe into a bottle,a far bit of oil vented.We couldnt road test,as its pissing down.
Now ill explain the complete set up guys.Its a 70 bike with the central oil tank.The CNW breather returns to the spigot on the filler neck.(the same place as original vent)Its a crush proof line with a direct route.
The original tank breather,is basically a hole with vents into the air filter pod.As I used a mikuni, I made a spigot, and then ran a hose to a small catch tank.
Yesterday, I attempted to blow air through the catch tank(lung version) I did so, but it wasnt that easy.Awaiting updates.I will bring this thread to a conclusion and hopefully an answer as it progresses.

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Thank you for following up!

It’s quite normal for oil to be it the cNw type breather. Especially if your bike wet sumps (well that’s a given really, more like how bad it wet sumps). It has no impact on its functionality.

In fact that’s one of its benefits, it’s great at containing a wet sump issue by providing for rapid egress of excess sump oil back to the tank. Thus avoiding blown primary seals etc.

Fast Eddie said:

It’s quite normal for oil to be it the cNw type breather. Especially if your bike wet sumps (well that’s a given really, more like how bad it wet sumps). It has no impact on its functionality.

In fact that’s one of its benefits, it’s great at containing a wet sump issue by providing for rapid egress of excess sump oil back to the tank. Thus avoiding blown primary seals etc.

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Hi Eddie.Engine has never wet sumped, enough to cause starting issues.It does have the Holland Norton works, anti return ball valve fitted to oil tank.

coomo said:

Hi Eddie.Engine has never wet sumped, enough to cause starting issues.It does have the Holland Norton works, anti return ball valve fitted to oil tank.

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Cool, so the wet sump feature isn’t useful to you. But my main point was to point out that oil doesn’t harm or hinder the the functionality (in cases that was a consideration).

coomo said:

Yes it is Norman.I visited yesterday.On removing the CNW breather and running the pipe into a bottle,a far bit of oil vented.We couldnt road test,as its pissing down.
Now ill explain the complete set up guys.Its a 70 bike with the central oil tank.The CNW breather returns to the spigot on the filler neck.(the same place as original vent)Its a crush proof line with a direct route.
The original tank breather,is basically a hole with vents into the air filter pod.As I used a mikuni, I made a spigot, and then ran a hose to a small catch tank.
Yesterday, I attempted to blow air through the catch tank(lung version) I did so, but it wasnt that easy.Awaiting updates.I will bring this thread to a conclusion and hopefully an answer as it progresses.

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Can you please take a picture of your oil tank of the filler neck and post it. The 1970 tanks I have seen do not have a spigot on the filler neck.

I can’t say I have seen more than about a dozen come through the shop (one here right now) so there is certainly a chance there may be some variations of that tank.

Matt

Its taken me an hour to post these! Im no good with this stuff,hope you can alll see it.This was oil system being built.Bike is not home yet.You can see spigot on front of tank, which goes to catch tank.You can see oil return, into filter under tank.Matt,if you look closely on top of second image,you can just see spigot of return junction of breather return

Hi guys.Apologies for delayed response.Work Projects getting in the way again.Anyhow,When I dropped bike at Normans,I was firm in my desire that the Comstock/CNW breather remains.If it was faulty or incorrectly assembled, then to check it.He Usually fits the later mk3/4 breather, for many years without issues.I wanted the CNW unit to remain.
I had an idea that the breathing was being restricted by the catch tank I installed, unless of course the restriction was in the oil tank.
Part of the service was to fit a Boyer.2 failed Pazons in less than 800 miles,left me less than confident.
I got the call on thursday, and collected the bike.Norman was happy with it, which generally means I will be.
The issue did in fact lie with the rubbish catch tank I fitted.Norman fitted one of his designs.Just ridden 50 miles.It actually seems to perform better than ever.The front Isolastics were 40 thou out.They were replaced too.We all know Commandos are the best Godamn bikes ever built, but im really over the moon how its riding.In fact Norman said, "You really need to ride another Commando,to realise how good it is"
He showed me a customers bike that had SS pipes fitted.The Andover units are awful.The tube is butt welded to the flange.Not suprisingly they crack.Norman supplys his
own whereby the tube inserts into the flange.Simple stuff, why Andover dont do this is beyond me.
Pictures below of current setup.
Just in case anyones interested the "50th Anniversary cafe" in my Avi (40 miles from new) sold at Bonhams last week.£10,000 dead.Add £1500 fees .

Always nice to hear about a problem being sorted. Glad you nailed it. Now to enjoy riding it !

Not good news on the sale of your 961 tho

Fast Eddie said:

Always nice to hear about a problem being sorted. Glad you nailed it. Now to enjoy riding it !

Not good news on the sale of your 961 tho

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Well,I did take a pill on the 961.However, ill put the money into another bike.Yknow.One I can actually ride!