Intake rocker breather

geo46er said:

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.

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Ahh problem is my bike never sits in the garage for a week its my main mode of transport never had a car licence...good points made though informative for all

Okay I kind of get it but still not 100%. Is their someone who could draw with crayon or pencil exctactly how this bunn system works?

The one picture shows air flowing into the rocker box, but does that a filter on it, does it connect into the breather or does that have its own catchcan, is the one way reed valve with this set up.

I couldnt get a clear picture of how it works by the bunn website.

thanks

Hi mcns,
The Bunn system has two one-way valves, one for the air to go in, and one for the air to go out. You could install them to flow air from the rocker box down into the case, or from the case up into the rocker box, or if you wanted to drill some holes you could make it vent from one side to the other. You definately want to filter the air in, so you could attach some sort of aftermarket filter, or simply attach to the stock airbox. Same thing on the discharge side, set up some sort of alternative catch bottle, or continue venting into the oil tank.

GB

So two years later has anybody actually fitted one of these Bunn systems? A Mate of mine has fitted one with the inlet to the plug low on the timing side crankcase and the out valve to the normal back of the timing cover position. After about 200 miles he's collected about 175ml of oil out of that pipe (bores and top end in very good condition) the plan was to avoid routing the vented gas back through the oil tank, but when there is that much oil involved............ The cost of £80 seems quite a lot for a couple of plastic valves and a few feet of pipe.

Having a one-way valve at one end and an open breather up top seems to be against what you'd be trying to achieve with a one-way valve. With a good one-way valve to take care of efficient crankcase venting, you'd want the rest of the engine sealed up reasonably tightly so that the best effect from the valve would take place.

Really great art ,keep up the good work and pay attention to copyright laws. People steal from the internet. Anything to achieve slightly negative crankcase pressure !

Of course the mythical Ms Peel will have an intake breather with just a filter on it as will always inhale w/o a check valve. Negative pressure eductor with fresh air flush though.

marinatlas said:

? where are the gurus.......

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I believe that one of the "gurus" put 85,000 miles on his Commando engine while pulling negative pressure in the crankcase with a reed valve.

Water and fuel that is contaminating oil will vaporize out of it when it gets hot and will leave a vented oil tank the same as a vented engine.

The power losses in a Norton engine from pumping air are eliminated when the crankcases are sealed up tight and there is nowhere left to pump air to.

When air is eliminated from the crankcase and it is running negative pressure, then you are turning the crankcase into a large air-spring. If there is a vaccum the pistons will lose power pulling against it but get it back when the negative pressure helps pull them back down, just like energy is not lost compressing a spring, the spring gives it back, think of the pistons being on a negative pogo-stick.

The early 650 Norton twins had a crankcase breather and a breather coming off the intake rocker cover, both dumping onto the ground in front of the rear tire, which made for some interesting riding. Next they came out with the froth tower oil tank part way through 1962 and ran the crank breather into that. When AMC started making Nortons they eliminated the rocker breather.

So Norton WAS trying to sort things out before they were shut down. The crankcase breather to the oil tank they started using on some of the 1962 SS Nortons would cut oil consumption, and the vent from the rocker cover would let contaminant vapor out while losing little oil. Despite this they certainly had a long way to go to get where Honda was overall.......

beng said:

The power losses in a Norton engine from pumping air are eliminated when the crankcases are sealed up tight and there is nowhere left to pump air to.

When air is eliminated from the crankcase and it is running negative pressure, then you are turning the crankcase into a large air-spring. If there is a vaccum the pistons will lose power pulling against it but get it back when the negative pressure helps pull them back down, just like energy is not lost compressing a spring, the spring gives it back, think of the pistons being on a negative pogo-stick.

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Expanding on beng's comments a bit, evacuation of the crankcase also aids in piston rings sealing and reduces windage.

With a depressed crankcase pressure the rings have more of a tendency to seat against the bottoms of the ring grooves and against the cylinder wall.

To verbally illustrate "reduced windage" in a crude way, wind is comprised of air and if there's no air then no wind thus when a droplet of oil slings off the crankshaft there will be little to no wind to keep it aloft. Oil droplets would tend to hit their mark in the crankcase and dribble down to be collected.

Sealed crankcases and reed valves should be fairly effective (with a single and 360 degree twin) in getting the crankcase pressure down significantly. Sealing the crankcases should be easy until you get to the lip seals. I never could get my head around how that should be done. I always questioned whether the lip seals would burn up as lubrication for the lip seals was always being drawn away into the engine.

Jim Comstock ran an evacuation pump on one of his bikes in the past. IVacume pumps may be standard fare on NASCAR engines and perhaps Formula 1.

I purchased one of the new reed valve type breather and will see about getting some crankcase pressure readings once we get the build complete and on the dyno.

One of the successful Suzuki dragbikes of 10 or so years ago ran three electric vacuum pumps on its crankcase. The team claimed quite an increase in power to the rear wheel.

Dances with Shrapnel said:

To verbally illustrate "reduced windage" in a crude way, wind is comprised of air and if there's no air then no wind thus when a droplet of oil slings off the crankshaft there will be little to no wind to keep it aloft. Oil droplets would tend to hit their mark in the crankcase and dribble down to be collected.

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Maybe more than keeping the oil aloft is frothing. I've seen investment slurry for lost wax casting being mixed in what looks like a small sealed Cuisinart. It looks like beer till a vacuum is hooked to it. The bubbles disappear instantly. Oil temps go down and power goes up.

A good illustration of windage would be those little solar windmills in what looks like a light bulb. The vanes are painted white on one side and black on the other. Photons hit them both equally. The black sides absorb the full kinetic energy, more or less. The white sides reflect most of it. The difference makes the vane spin. The only way this could work is the fact they are working in a vacuum. No air to push around. There was a time when F1 engines were built like stacks of V-twins, each with sealed crankcases so they wouldn't try to push air. There is a NASCAR rule limiting the scavenge pumping. They're not trying to suck out oil, it's air.