CNW Breather issues

[coomo]

My 1970 750 was rebuilt 1000 miles ago.Engine was completed by the most well known ex factory Norton racer/designer in UK.We did the CNW crankcase breather mod.The one ,which is machined into case.
Ever since the rebuild,on occasions, the engine has puffed out some smoke.Despite every possible reason being investigated,it persisted.
It has just gone back, for a tune as it chewed up its 2nd Pazon.Boyer has now been fitted.Pazon were very good & replaced unit.My initial thoughts was that vibration was knocking out the coils over time.1st unit lasted 150 miles,2nd about 1000.Anyway I digress.
My engine guy was alarmed at the smoke,and wasnt happy that an engine he built be on the road with this issue.Plus the plugs were always very sooty,despite timing/carb setup being on point.Me I wasnt overly concerned as I had got to live with it.
Anyway, he asked if he could remove the CNW breather and refit a factory type.I agreed.That was completed, and smoking issues ceased.
The central oil tank breather which previously vented to atmosphere,now vents to a small catch tank.There is also a Holland Norton Works, anti sump valve fitted to oil tank outlet.
I always had great confidence in CNW parts still do, and shall continue to use them.Im just perplexed as to why for some reason the CMW breather impacted the bike this way.Not a criticism just a question.Input appreciated guys.
Just for info.The 2018 50th Anniversary, in my avatar(40 miles from new) will be sold at Bonhams next month.If anyone wants one!

 

[cNw]

This truly does sound strange. With several hundred of these running with great results out there, I have never heard of one with the issues you mention

I am wondering how you had the breather hooked up to the central oil tank ? This tank is of course a bit different in design than the standard right side mount

Matt

 

[Matchless]

I have reed valve breathers fitted to the bottom rear of the crankcase on three of my Norton twins. It's the best modification you can make to any 360 degree twin in my opinion. I think you may need to look at the routeing out of the breather hose, as it needs to go to a tank, be it oil or just catch tank which is vented to atmosphere.

Martyn.

 

[SteveA]

My 1970 750 was rebuilt 1000 miles ago.Engine was completed by the most well known ex factory Norton racer/designer in UK.We did the CNW crankcase breather mod.The one ,which is machined into case.
Ever since the rebuild,on occasions, the engine has puffed out some smoke.Despite every possible reason being investigated,it persisted.
It has just gone back, for a tune as it chewed up its 2nd Pazon.Boyer has now been fitted.Pazon were very good & replaced unit.My initial thoughts was that vibration was knocking out the coils over time.1st unit lasted 150 miles,2nd about 1000.Anyway I digress.
My engine guy was alarmed at the smoke,and wasnt happy that an engine he built be on the road with this issue.Plus the plugs were always very sooty,despite timing/carb setup being on point.Me I wasnt overly concerned as I had got to live with it.
Anyway, he asked if he could remove the CNW breather and refit a factory type.I agreed.That was completed, and smoking issues ceased.
The central oil tank breather which previously vented to atmosphere,now vents to a small catch tank.There is also a Holland Norton Works, anti sump valve fitted to oil tank outlet.
I always had great confidence in CNW parts still do, and shall continue to use them.Im just perplexed as to why for some reason the CMW breather impacted the bike this way.Not a criticism just a question.Input appreciated guys.
Just for info.The 2018 50th Anniversary, in my avatar(40 miles from new) will be sold at Bonhams next month.If anyone wants one!

By CNW style, do you mean you have had a reed valve breather? And that you have now removed it?

And by 'puffed out smoke' do you mean a smokey exhaust?

Where do you think the oil got into the combustion chamber, past the rings or down the inlet valve guides?

You don't say, but do the plugs look good now?

 

[cliffa]

It sounds as though for some reason the reed was not opening.

 

[Schwany]

In my limited Norton tuning experience a bad breather arrangement usually results in loss of top end power. Motor goes flat sooner than it should and won't pull anymore. It's quite noticeable until resolved. I can't see how Matt's reed breather could fail to work properly. It is a simple solid design. Very curious indeed.

I was going to say the reeds were installed backwards (sort of like cliffa said), but I thought that would have been checked.

 

[Fast Eddie]

Do you have the breather that was removed? If so you should be able to see how it works, it’s a very straightforward thing, air gets out but won’t get back in. I run a reed valve breather on mine and cannot see how it could be your issue.

What led your engine builder to the hypothesis that removing the reed valve would cure the issue?

You haven’t actually said how your engine breathes now ?

Why have you fitted a catch bottle to the tank vent? And does it actually catch any oil?

 

[coomo]

This truly does sound strange. With several hundred of these running with great results out there, I have never heard of one with the issues you mention

I am wondering how you had the breather hooked up to the central oil tank ? This tank is of course a bit different in design than the standard right side mount

Matt

Yes Matt.Breather runs to oil tank., routing via some rubber/braided line.However.Now im beginning to wonder if the issue maybe bad routing or bad line.I had recent oil leak with some lines we used on a Porsche 911.Ill investigate further.

 

[coomo]

Do you have the breather that was removed? If so you should be able to see how it works, it’s a very straightforward thing, air gets out but won’t get back in. I run a reed valve breather on mine and cannot see how it could be your issue.

What led your engine builder to the hypothesis that removing the reed valve would cure the issue?

You haven’t actually said how your engine breaths now ?

Why have you fitted a catch bottle to the tank vent? And does it actually catch any oil?

Havent collected bike yet Eddie, I will check when I do.The "factory" breather hasnt been permanently fitted yet,as far as I know.My builder was racer/factory tech.His builds dont seem to suffer from issues that many do.Plus hes old school and suspicious of new "fangled " ideas!
The catch bottle initially collected a far amount.However,after few hundred miles it lessened.Maybe half egg cup every few hundred miles.The catch is just for the oil tank venting.As factory it just exits straight into the air filter.

 

[coomo]

By CNW style, do you mean you have had a reed valve breather? And that you have now removed it?

And by 'puffed out smoke' do you mean a smokey exhaust?

Where do you think the oil got into the combustion chamber, past the rings or down the inlet valve guides?

You don't say, but do the plugs look good now?

Yes reed breather.I presume its been blocked off.Ive got to collect bike yet.Yup smokey exhaust.Havent seen plugs yet, nor do I know route of oil.

 

[coomo]

Do you have the breather that was removed? If so you should be able to see how it works, it’s a very straightforward thing, air gets out but won’t get back in. I run a reed valve breather on mine and cannot see how it could be your issue.

What led your engine builder to the hypothesis that removing the reed valve would cure the issue?

You haven’t actually said how your engine breaths now ?

Why have you fitted a catch bottle to the tank vent? And does it actually catch any oil?

Ill see valve when I collect bike.

I have reed valve breathers fitted to the bottom rear of the crankcase on three of my Norton twins. It's the best modification you can make to any 360 degree twin in my opinion. I think you may need to look at the routeing out of the breather hose, as it needs to go to a tank, be it oil or just catch tank which is vented to atmosphere.

Martyn.

Its routed back to oil tank.

 

[RoadScholar]

I was going to say the reeds were installed backwards (sort of like cliffa said), but I thought that would have been checked.

The reed can be installed 4 ways, IIRC, only one of which is correct. The instructions cNw supplies, if followed, remove the elements of chance. I have used several of cNw's reed valves with 100% success. If installed incorrectly the reed valve will actually increase crankcase pressure; work backwards.

If cNw didn't do the machining/conversion the timing side of the engine may not have had the benefit of tapping and plugging of the holes that allow direct communication with the chamber the crank lives in. Almost useless to speculate any further with out more data. I am glad that you are back on the road without the appearance of riding a 2 stroke.

The anti drain valve will raise some dust on the forum unless you have backed it up with an oil pressure gauge?

Best.

 

[Fast Eddie]

Ill see valve when I collect bike.

Its routed back to oil tank.

Routed back to the tank yes… but from where / how?

I didn’t realise you hadn’t got the bike back yet. You might wanna leave the victory flags in the drawer until you’ve ridden it yourself, on routes you normally ride, how you normally ride it.

My local Mercedes dealer has ‘fixed’ a fault on my wife’s car 3 times recently… except they haven’t…!

 

[cNw]

Yes Matt.Breather runs to oil tank., routing via some rubber/braided line.However.Now im beginning to wonder if the issue maybe bad routing or bad line.I had recent oil leak with some lines we used on a Porsche 911.Ill investigate further.

As Fast Freddie mentions, where it’s attached to the oil tank is absolutely critical. There is only one place it can go to in order to operate properly

You also mention that your catch can at the end of the atmospheric vent was in fact filling with oil. This typically only happens when your oil tank is overfull. It being a vent line, should be mostly air/ oil mist. Sure over miles it can add up but should not just fill up in a short amount of time

Keep us posted as to what you find

Matt

 

[Time Warp]

That is a camshaft breather engine in stock form with a frame cross tube that does not allow the large sump plug location to be used (clash) so you would (or not) have to wonder what breather is added (surely not the back of the engine cases machined) and where the hose is going to.

Stating the obvious, the easiest way to get smoke is to introduce oil into the combustion cycle be it by the inlet tract, guides or past the piston rings from the sump and the last two would not be sporadic taking for granted the plumbing from the breather is correctly routed.

 

[Fast Eddie]

That is a camshaft breather engine in stock form with a frame cross tube that does not allow the large sump plug location to be used (clash) so you would (or not) have to wonder what breather is added (surely not the back of the engine cases machined) and where the hose is going to.

Stating the obvious, the easiest way to get smoke is to introduce oil into the combustion cycle be it by the inlet tract, guides or past the piston rings from the sump and the last two would not be sporadic taking for granted the plumbing from the breather is correctly routed.

He mentioned it’s the cNw breather, so that’s the back of the case job, it’s NYC that sell the sump plug type.

 

[Fast Eddie]

Just thinking about these symptoms again, personally, the syptoms of poor breathing I have observed in the past have been oil leaks. I’ve never seen poor breathing cause smoking (Although smoking does casue poor breathing… in humans… but that’s another thread entirely).

And I have good experience in this field. When I was 15-16 I built a Tiger Cub and not knowing much about engines, I built it without ANY engine breather. I couldn’t work out why it kept pissing oil everywhere despite copious amounts of bathroom silicone. My Japanese mounted mates all offered various helpful comments like ‘Waddya expect from Brit shit’ Etc ! IIRC it was my Dad who spotted the (literal) school boy error !

Even recently when I conducted a (failed) experiment using the rocker boxes for breather outlets on my T140, oil leaking past the seal and into the dry primary was the symptom, not excessive smoking.

I find it interesting that in removing the Reed valve breather, the engine builder also changed other aspects of the plumbing, added a catch bottle, etc, so I suspect something else is afoot here.

Jus’ sayin’.

 

[gortnipper]

Your engine will smoke if the oil tank does not vent to air. Breather tube to tank, tank to catch bottle. I made that mistake on my mk3 when I first had it in the 80s...

 

[Time Warp]

He mentioned it’s the cNw breather, so that’s the back of the case job, it’s NYC that sell the sump plug type.

Yes, I just did not want to believe it being a 20M3S engine with the timing side blanking plate.
The engine case is thin enough as is without fly cutting and make holes in it.

Perhaps CNW could consider a billet one piece reed valve unit that replaces the T/S plate, the divider wall would need drilling to feed it.
It would simply follow the stock 850 routing. (but the cam shaft breather outlet by the engine number location would need to be plugged)
#
The first thing to do would be unplugging the hose from the CNW breather (Tank end) and verifying what is coming out the end of it with the engine running.
A good deal of calamities turn out to have simple remedies after fault tracing .

 

[Onder]

Agree on checking that hose. And then check that each leg of every hose is clear. On start up my sump plug type valves pukes a fair amount of oil back the tank. Wet sumping of course. But once clear there is very little to none. Stock routing on the later engines tank vents to the air cleaner. When I pulled the aircleaner off yesterday I could see that vapour does get sucked into
the carbs and over time there is some small residue. The bad part is you are digesting oil and the good part is you are positively
venting the oil tank. With a good engine there isnt much vapour to worry about. I will put a catch can on this line now just to see
how much I get.