Intake rocker breather

acadian · Mar 16, 2010

I'm looking for some feedback/opinions/experience on installing an intake breather on the inlet rocker cover. For those of you who have installed such a device, are you using it as an intake or exhaust breather? Inline valve?

I've got an XS650 valve installed in the crank breather line but am curious as to whether or not I should provide intake breathing solution to the system. (similar to the Bunn kit) Thanks for the input.

geo46er · Mar 16, 2010

Hi Acadian,
I'm glad you started this thread as I think crankcase ventilation is something that needs discussing here. The XS, Motormite, Ducati, CNW, and every other type of one-way valve being mounted on Norton cases and/or breather lines is NOT for crankcase ventilation (as in an automotive system), but used to reduce crankcase pumping losses by eliminating (or at least reducing) the negative (air back into case) flow, theoretically creating a slight in case vacuum. Unfortunately, for us this does NOTHING to vent all the nasty and moisture filled blow-by gases from the crankcase. To add insult to injury most Norton riders vent what does make it out straight into the oil tank. The Bunn system seems to address crankcase ventilation by establishing a through case air flow similar to an automotive system. Unfortunately, unlike an automotive system (or any multi cylinder system), boxer, parallel, and to a lesser extent V twins have to deal with massive pumping losses. I believe the Bunn system would effectively vent the crankcase, but would do nothing to reduce pumping losses. One of those damned if you do, damned if you don't situations. Perhaps if your Norton is prone to oil leaks, install one one-way valve and reduce crank pressure, on the other hand if your engine is somewhat tired (excess blow-by and/or moisture) you may be better served with the Bunn system.

GB

kommando · Mar 17, 2010

The oil pump moves a lot of air with the related blow by contaminates back to the oil tank and then to the air intake, the return side of the pump has twice the capacity of the feedside and the excess takes the form of air.

mike996 · Mar 17, 2010

I had never heard of the Bunn kit until reading this post. In reading about it, it seems like an excellent way to address crankcase breathing. Their site has a lot of information that seems to show that he (Bunn) did a lot of research in this area. I was quite impressed. Of course, his site IS trying to sell something but the data seems well done and certainly worth consideration if looking into "better" crankcase breathing. For others who may also be new to the info, Go here and then to his BLOG http://bunnbreather.bigblog.com.au/index.do

More info here: http://www.britishcycle.com/Products/Bu ... er_kit.htm

Gino Rondelli · Mar 17, 2010

Our first meeting last Sunday and one of the guys had fitted a breather to his intake rocker cover, just ran it to a small catch bottle. He reckons its got rid of all the annoying persistent leaks.

acadian · Mar 17, 2010

geo46er said:
Hi Acadian,
I'm glad you started this thread as I think crankcase ventilation is something that needs discussing here. The XS, Motormite, Ducati, CNW, and every other type of one-way valve being mounted on Norton cases and/or breather lines is NOT for crankcase ventilation (as in an automotive system), but used to reduce crankcase pumping losses by eliminating (or at least reducing) the negative (air back into case) flow, theoretically creating a slight in case vacuum. Unfortunately, for us this does NOTHING to vent all the nasty and moisture filled blow-by gases from the crankcase. To add insult to injury most Norton riders vent what does make it out straight into the oil tank. The Bunn system seems to address crankcase ventilation by establishing a through case air flow similar to an automotive system. Unfortunately, unlike an automotive system (or any multi cylinder system), boxer, parallel, and to a lesser extent V twins have to deal with massive pumping losses. I believe the Bunn system would effectively vent the crankcase, but would do nothing to reduce pumping losses. One of those damned if you do, damned if you don't situations. Perhaps if your Norton is prone to oil leaks, install one one-way valve and reduce crank pressure, on the other hand if your engine is somewhat tired (excess blow-by and/or moisture) you may be better served with the Bunn system.

GB

Thanks for the reply, this is what perplexes me. Having the XS650 breather installed in my crank breather line will do nothing to help ventilate the crankcase itself, correct? Therefore, adding an one way intake breather to the inlet rocker would not help much without a second one way outlet breather (in addition to the existing line) elsewhere on the crank?

***edit to clarify with my meager drawing skills, is the set up indicated enough to accommodate proper crank case ventilation?

mike996 · Mar 17, 2010

What you drawing shows is essentially what the Bunn system does...looks like a good idea to me.

Reading all of the Bunn blog makes it very clear that a PCV valve is useless on these bikes since a car engine works very differently from a Norton engine. On the car, the PCV is always under vacuum from the int manifold. On a Commando there is no such vacuum applied and crankcase venting is a completely different function. The blog states in one of the entries - the only thing that the Norton engine and a car engine share is that they are both Otto-Cycle engines. NOTHING else is common to them so applying a car breather system to a commando motor is useless and counter-productive.

sidreilley · Mar 17, 2010

Interesting this has come up. My 69 came with a small barbed fitting on the intake rocker to provide a vent to something but it had been squashed and nothing was attached by the time I got it. The actual venting hole was probably around 1/8 " and I wondered what the PO was thinking or trying to do. It didn't seem to me that this small size could actually provide much venting from pressure. Is the idea to vent it to the manifolds or back to the oil tank? I can't tell from your detailed drawing :wink:

acadian · Mar 17, 2010

sidreilley said:
Interesting this has come up. My 69 came with a small barbed fitting on the intake rocker to provide a vent to something but it had been squashed and nothing was attached by the time I got it. The actual venting hole was probably around 1/8 " and I wondered what the PO was thinking or trying to do. It didn't seem to me that this small size could actually provide much venting from pressure. Is the idea to vent it to the manifolds or back to the oil tank? I can't tell from your detailed drawing :wink:

I won't be giving up my day job to freelance as an artist anytime soon... The idea is to provide not just crank case outlet breathing through the crank breather to the oil tank, but to provide complete ventilation by using the rocker breather as a fresh air intake. As far as the oil tank itself, it's vented separately to a catch bottle.

swooshdave · Mar 17, 2010

acadian said:
Thanks for the reply, this is what perplexes me. Having the XS650 breather installed in my crank breather line will do nothing to help ventilate the crankcase itself, correct? Therefore, adding an one way intake breather to the inlet rocker would not help much without a second one way outlet breather (in addition to the existing line) elsewhere on the crank?

***edit to clarify with my meager drawing skills, is the set up indicated enough to accommodate proper crank case ventilation?

Not sure what you mean. The crankcase breather will let any excess gases/pressure out. This includes the blow-by.

ML · Mar 17, 2010

On my 850 Mk2 I run a 1/4' hose from the inlet cover direct to a 600mm catch bottle. Then I run a outlet hose from the bottle to atmosphere. I have been using this system for 6 years and find it very effective. I used clear hose so that I could see what fluid movement may occur. The most interesting thing was the obvious moisture as an emulsion being expelled. I wanted to minimise contaiminated blow by being returned to the oil tank and relieve internal pressure. I do run the stock timing side hose into the tank, but I always felt this was inadequate for the volume and pressure in the crankcase, hence relieving the top end as a means to reduce overall pressure. Another benefit has been the total reduction of oil weeping on the motor. I mentioned in an earlier posting that the top end breather expells about 250ml of fluid every 500Kms (my motor is pretty well used but emits no smoke or vapour). That 250ml was a typo, its actually 150ml or 1/4 pint every 300 miles.

I have no pro or cons for a one way vacuum device, (as in XS650) but in relation to my set up, can't see that it would make much difference. I have always subscribed to the concept as in car engines, a motor does need to breathe. In the case of the Commando, it is to make the variation between pressure cycles as little as possible.

Mick

grandpaul · Mar 17, 2010

I typically run my crankcase vent tube through a one-way valve (trying a new reed valve setup now), then down the bottom to one side (plug up the oil tank filler neck vent pipe).

chris plant · Mar 17, 2010

hi acadian,looking at your drawing and the positioning of the breather pipes,have you fitted a one way valve{reed}to the timed breather,if so why.regarding the breather pipe to the inlet rocker cover what are you expecting from this as i dont see a one way valve atached to it.

highdesert · Mar 17, 2010

GrandPaul, are you saying that you run a hose off your one way crank breather valve directly to open air
somewhere on the side or bottom of you bike, and simply bypass it going to the tank?
Seems very simple, and without returning those crank gases back to the oil tank.............?

grandpaul · Mar 17, 2010

Yes, just so.

Standard practice on the timed breather of a classic Triumph.

If your breater pipe is spitting anything after traveling 14" in the vertical, you have other SIGNIFICANT problems that need to be addressed.

marinatlas · Mar 19, 2010

Hi there , may be dreaming or my memory failing , but seen somewhere about nor(ton that , inlet rocker breathing can impede the oil flowing down and past the cam followers , I mean without any vacuum in the cases........story or true?? where are the gurus.......

acadian · Mar 19, 2010

ludwig said:
this is a picture out of a Gus Kuhn catalogue early 70-ties .
It shows ex rocker covers with vent tubes .
They also had finned inlet covers with vents ( I bought one ).
A year or so later , when a friend of mine asked for them in their shop on Clapham road , they where no longer available : apparently they gave problems .

I've heard something similar, but the Bunn site addresses these issues in a tech article where he claims the volume of air in the pushrod tubes was too little to impede the flow of oil...

marinatlas · Mar 19, 2010

hello Jan, I also have those covers on the shelf , and before fitting them , I ask about the compatibility with the XS breather valve , mine is put just behind the timing cover (850 case), and on my mate 's engine (750 post 200.000) we do the same arrangement as Jean Droit, after he had nicely sent us good pictures of his own design.........I had again read the Bunn's breather site , and now scratching my head, about letting some air (fresh) going inside?? may be Jim Comstock will come and explain us........the engine with Schmidt 's pistons /rods is still on the bench, while a friend of mine had milled a new center flywheel from steel ( ala maney but cheaper !), during that time , I had seen that guy in Germany making nice cranshaft ...that's a never ending "quête du Graal". On the other end the G15 is nearly completed , and will be the "Commuter " bike with single carb, and stronger studs for the inner chaincase (following your advise), if I was clever enough to put some pics....Bonne journée à toi, Pierre.

plj850 · Mar 19, 2010

OK now this is getting confusing, maybe I am being really dumb but my Commando 850 has an Oil Tank Breather so my Crankcase Breather (with XS650 Valve) pumps into the Oil Tank and I assume a large quantity of this air/contaminated air is expelled through the Oil Tank Breather????. (My Oil Tank Breather vents to rear of bike) I cannot see why not....In fact if for any reason your Oil has been contaminated with water this is clearly apparent with vapour leaving the pipe....In fact when I was looking to buy a Triton one of the first things I would check out was what was coming out of the Crankcase Breather..oddly enough one bike had nothing coming out of the breather because the owner had shoved a length of rod up it hide the tell tale signs of severe blowby. :roll: :roll:

geo46er · Mar 19, 2010

Hi plj850,
In a perfect world your one-way valved engine breather tube pumps no oil to the tank. During the first couple of piston downstrokes the air is pumped from the cases establishing a slight vacuum which reduces pumping losses and keeps all the case joints and seals nice and oil tight.
In the real world the bike has been sitting a week and the crankcase is half full of wet sumped oil, the first couple piston downstrokes send a gusher of oil up the breather tube (72 models). Once the engine is running piston blow-by reduces or completely eliminates the case vacuum, and directly contaminates the oil in the engine with moisture and other nasty gases, then indirectly contaminates it by being vented into the oil tank.
Regarding your observations of breather output, when the engine is running oil is flying all over inside, therefore it is beneficial if the exhausted breather air/oil mist passes through somesort of condensor/oil trap. Venting the breather into the oil tank was Nortons answer.

Intake rocker breather

Similar threads