Author Topic: Bunn Breather - or something like it  (Read 6754 times)

Offline BSA_54A10

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Re: Bunn Breather - or something like it
« Reply #15 on: 19.04. 2014 11:47 »
I doubt that an outsider will go into production if he keeps the same specs.
I will be chastising Rex for not letting me know it was up for grabs as I would have gone deeper into hock to keep them into production.
the killer is the material that Rex uses for the valve.
The stuff is dearer than diamonds weight for weight .
Rex found a company that was using the material and he bought their scrap & hand cut the valves from it then on sold the reminants to some one else.
If you make them from complete sheet then you would be looking at over $ 200 Aus which is way too much for most BSA owners to fork out.
Racers will happily pay that for the extra Hp but not enough volume to make them viable.

If his blog is still up he goes through what he tested and why each one of them failed so you will find a few options that were "second best"
Bike Beesa
Trevor

Offline roadrocket

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Re: Bunn Breather - or something like it
« Reply #16 on: 20.04. 2014 09:31 »
Thanks folks!

Just to reasure myself: The valve behind the little inlet air filter is a non-return valve that lets air in but not out. The other (exhaust) valve is also a non-return valve that lets air out but not in? Whether you want to let the polluted outlet hose run to the oil tank or atmosphere is optional seen from a viewpoint of engine brething? This should be done only if you cut off the timed breather?

Otto in DK
Otto in Denmark

Offline BSA_54A10

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Re: Bunn Breather - or something like it
« Reply #17 on: 20.04. 2014 10:22 »
yep, that is the way it is done.
you can plug the exhaust into the oil tank so the condensed oil returns to the right place but if you do it this way you need to make sure the oil tank breather is the same size as the exaust gas breather tube or you will be pressurizing the oil tank.
Bike Beesa
Trevor

Offline kiwipom

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Re: Bunn Breather - or something like it
« Reply #18 on: 20.04. 2014 11:49 »
hi KiwiGF, you say(One other thing that seems odd is the breather runs at half speed so if it has just one hole it must only allow gases out every other revolution, would making 2 holes in it make it work better) i have two of these parts and both have 2 holes opposite each other in them so is that not normal? cheers
A10.G.Flash(cafe racer)Honda 250 vtr. Yamaha Virago XV920.

War! what is it good for?Absolutely nothing, Edwin Star.
NewZealand

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Re: Bunn Breather - or something like it
« Reply #19 on: 20.04. 2014 12:04 »
That's how I've got it Trevor.
Mate said the reed valve is the size of a matchbox. I'll check it out in a fortnight.
Cheers
Kwipom two holes opposite is good
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Offline BSA_54A10

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Re: Bunn Breather - or something like it
« Reply #20 on: 21.04. 2014 09:18 »
Just had a thought.
Rex did a couple of breathers for modern Enfields which I think got added to the Deluxe & the electric start models as standard so you might be able to get the valves from your local Oilyfield dealer or at least from the Enfield sites on the www.
He was going to do them as an aftermarket jobbie but could not get any one in OZ to make silver tube so the units did not stick out like the proverbial doggies.
Bike Beesa
Trevor

Offline Dynamo Regulators Mike

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Re: Bunn Breather - or something like it
« Reply #21 on: 23.04. 2014 21:30 »
I thought the valve pictured by Kiwipom worth a closer look so bought one from fleabay.
Seems promising, light spring opens readily, don't know about a 'flea fart' Musky, but perhaps a fly's?
Said to be fuel/diesel resistant but wonder how well it might cope with blow by fumes.
This is intended for my smoky B50 by the way. Don't have any trouble with the A's breather, as long as all end float taken up of course.
This is what it looks like inside:
Mike Hutchings
A10, B50, T800; 1,2,3 (& DVR2)
Director, DRL www.dynamoregulators.com

Offline victortrry

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Re: Bunn Breather - or something like it
« Reply #22 on: 30.04. 2014 12:32 »
I have an early royal Enfield and they have thing called a duckbill breather, just a rubber hose with a flattened end .
When I got the Enfield I could not get it to start because this particular breather was missing. It does all the things that that the bunn breather did and they cost about $2.50 each


Victo

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Re: Bunn Breather - or something like it
« Reply #23 on: 30.04. 2014 20:55 »
G'day Mike. I like the look of that valve but I don't think the lift is sufficient to allow the required flow/volume.
G'day Victor. The pressure required to open a duckbill is dependent on the material used. Another would be required in reverse to allow fresh air in.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
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Re: Bunn Breather - or something like it
« Reply #24 on: 30.04. 2014 22:33 »
Another would be required in reverse to allow fresh air in.


Except, of course, you don't need fresh air let in.

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Re: Bunn Breather - or something like it
« Reply #25 on: 01.05. 2014 20:46 »
Can you breath out, and now out again, and again, No don't breath in, just out. passed out yet?
So on the up stroke we're fighting vacuum & compression!! So what is the duckbill letting out?? Blowby the rings. Now add vacuum = more blowby. then there's all that acidic gas trapped in there breaking down seals and oil more quickly.  *fight*
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
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Muskys Plunger A7

Offline Nourish

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Re: Bunn Breather - or something like it
« Reply #26 on: 02.05. 2014 09:08 »
I must  admit I'm not getting this either, Why do you want a valve on the crankcase to let out the positive pressure to create a vacumm if you're only going to let it in again with another untimed valve - why not just have the system open to the air?
My BMW boxer twin(airhead) has just the exit reed valve.

Offline BSA_54A10

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Re: Bunn Breather - or something like it
« Reply #27 on: 02.05. 2014 10:58 »
If you want the full explanation then go to Rex's blog. He has left it on the web for the benefit of other Pommie bike owners.
The whole story goes like this.
He bought a job lot of unit singles and kept a B44 & B50 for himself.
After a rebore & two attempts at seating the rings he found oil emerging from under the head nuts ( B50's are through bolted ).
This is because when BSA made the studs thicker they did not move the centres out, just drilled bigger holes which end up being too close to the mouth of the crank case.
They oft leak due to failure of the cylinder base gasket, failure of the studs to make an effective seal agaist the crank cases or the case itself cracking between the mouth & the stud hole.
The usual trick is to pull the studs , drill a small counter sink & fit some really thin O rings. or acorm nuts on the head with copper washers underneath.

Rex was not interested in pulling the motor apart again and wondered why there was enough pressure to force oil all the way up the stud and then out from undeer the nut.

What he larned was breathing theory had never been investigated properly from the days of oil slingers and while it still stood up for slow reving bikes with no oil seals, it did not stack up for modern bikes with modern seals.
With oil seals fitted there is no reason for having negative pressure in the crank case in fact it robs the engine of power, up to 2 Hp on some engines. ( Got your attention Musky ? )
He then went off on a crusade to fix this problem, not treat the symptoms as my "fixes" did.
Thus he found out the best practice was to allow air in then allow it back out and by doing this blow by from the rings was almost eliminated as most of the blow by happens at or near BDC as the piston rises but not enough to have compression force the rings to seal against the bore and of course on exhaust stroke, the piston rings do not make an effective seal and any reduced pressure under the piston, sucks the gas past the rings into the crank.

Even worse for timed breathers, because air actually has mass, it has a resistance to being moved and will compress slightly before it starts to move so the pressure pulses inside the crank end up being out of phase with piston movement so timed breathers only work properly over a speciffic range of crankcase speeds and these will change with bore : stroke ratios.
Flapper valves ( as fitted to the singles ) had the same fate. Up to around 2000 rpm the M series valve works very well however by the time you get to around 4000 rpm it is "fluttering " 100% out of phase with piston movements.
This is basically what the strokers found out with transfer ports & why they spent a fortune developing variable port engines.
Rex tested every available check valve ( brake valve to the USA readers ) to try and find one that worked from 500 rpm to 7000 rpm in an engine . ( guess who was a guniea pig for the preunit singles )
Every one on the market ( the complete market, not just automative ones ) failed miserably.
So thus the design of the various valves and eventually the entire kit.
The hope was to make a simple drop in replacement unit but that just did not work.
Further more the exhaust tube should be treated ( and thus tuned ) exactly the same as an exhaust pipe ( listening Musky ) to gain the maximum efficiency.
At one time we actually fitted some clear tube and watched the pulse nodes traveling up and back down the tube.

Now if you are thinking of making your own reed type valve, the teflon coated silk fabric that they make the impulse pump diaphragm valves out of would be about the best material you could find without going to the ultra expensive stuff that he used.
Bike Beesa
Trevor

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Re: Bunn Breather - or something like it
« Reply #28 on: 02.05. 2014 18:01 »
I have little faith in the "full explanation."

Large breathers, with or without one-way valves, are well known to reduce oil leaks.

 The desirability of drawing fresh air through the engine sounds like superstition. Why would I want cold Scottish fog to enter my engine?

Mr Bunn appears to be ploughing a lonely furrow if he purports that a partial vacuum in the crankcase reduces power.

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Re: Bunn Breather - or something like it
« Reply #29 on: 02.05. 2014 18:10 »
Can you breath out, and now out again, and again, No don't breath in, just out. passed out yet?

Is that just an example of your humour? Or do you think motorbikes faint if they don't breath in and out?

Quote
So on the up stroke we're fighting vacuum & compression!! So what is the duckbill letting out?? Blowby the rings. Now add vacuum = more blowby.

It is widely accepted that the opposite of those effects are apparent. http://www.carcraft.com/techarticles/ccrp_9903_moroso_vacuum_pump_test/

Quote
then there's all that acidic gas trapped in there breaking down seals and oil more quickly.  *fight*
Cheers

Sounds like a feasible theory. What were the results of the controlled experiments?