The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: roadrocket on 16.04. 2014 23:20
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Hello,
The Bunn breather kits are no longer available, but you can buy a very long and expensive book that tells you how to rig every bike you like, and all the science behind. The short version can not be had via Kindle for some reason. Now, have anybody fitted one to an A10, and will they reveal which parts are needed to rig one up?
Otto in DK
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Are you sure about that ?
Rex & I keep in touch since he went back to NZ & he has not said anyhting about stopping production , although he is now in the middle of making a movie.
He was having them made by a local factory.
Nothing special in the kits except for the valves & the material he finally settled on ( no I will not tell you what it is ) to make them out of.
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A friend has been trying to get one for a while and phoned Rex.I had heard he sold it off and the new owner has shelved it.
The system is so simple (the valves are a work of art and far from simple) fresh air in one way, gaseous fumes out another way.
Very light poppet or reed valves would work (just not as well).
Cheers
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I would happily buy one, but as they are no longer available, I thought that no harm could be done by making up sometjing similar. The guidebook is not available either, except for the 600 page version which is very expensive, and not what I need.
Otto in DK
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A friend of mine had one fitted to rocker box one to crankcase breather and the crankshaft oil seal popped out, presumably due to excess pressure caused by the crankshaft bunn breather blocking up, this was with new breathers on a newly rebuilt engine.
The oil seal popping out is a safety feature Ive been reliably informed, it is deliberately not securely held in place.
The bike now runs fine without the crankshaft breather.
So my 2 cents worth is that the (extremely extensive) theory on these breathers is probably fine, but in practice they are just another point of failure.
Maybe some engines benefit from them some don't? Maybe the engines that suffer from above average blow by?
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hi guys, a bit of research came up with this, cheers
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See this this link for the Bunn breather, they are expensive £89 but have been developed specifically for motorcycles by Rex Bunn in American.
Shropshire Classic Motorcycles are the UK agents for Bunn breathers, their website is www.triumphbonneville.com/
and you need to go to the T140 Shop tab on the left of page and then put breather into the search box and it will bring it up.
mod edit. insert picture
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Here is my set up.
1: intake to front tappet cover. Nice clean cool air going in at the hottest spot of the motor.
2: exit bad air out normal exit point. Piped to oil tank. Or to atmosphere if wanted.
3: bad air enters oil tank. A std tank could be modified.
4: bad air and oil fumes exit oil tank.
5: exit to atmosphere.
The only internal mod was to cut the timed breather off at the holes so the ports are always open.
No problems like blown seals. Less oil leaks. Quicker revving. You get used to the sound of the valves.
Cheers
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hi guys/musky, one guy i came across made his setup from these parts from Ebay,cheers
p.s.musky,can you explain the mod to the timed breather a bit more,cheers
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Hi this is my 1st post, I have Bunn breathers fitted to both my BSA's The A10 is a 1954 S/A basket case bought off Trade me, as it was a budget rebuild only new rings & big end bearings were fitted, on start up it breathed as you would expect from the crankcase leaving oil leaks when ever I stopped after fitting the Bunn breathers the leak was 99% cured I fitted the inlet in the back end of the timing chest & the outlet from the rocker box. I piped the original crankcase breather with 5/16 copper tube & then plastic tubing down to terminate adjacent to the rear chain which it lubricates nicely. On consultation with Rex I tried blocking the factory crankcase breather but it over pressurised the engine on a long trip & leaked out of the head at the back by the pushrods & on to the magneto slip rings causing misfiring. I would certainly recommend these breathers as they do control oil leaks by reducing crankcase back pressure. My A10 has now done 8 thousand miles which has given this 73year Kiwi A lot of pleasure.
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The non return valve pictured would work but it would need a very light spring. The Bunn valve opens with a flea fart. I cut the timed breather off at the bottom of the holes (see pic), that way the flange and cork are still eliminating any camshaft end float, but the port is always open.
Cheers
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hi guys/Musky, thanks for the pic it explains a lot.(He spent a day or two with Rex and was able to obtain a kit) perhaps you could inform me of his add he might be just down the road then i can contact him to see if he has anymore kits. I didn't realise that the engine breathing was the cause of all the troublesome oil leaks, having now read a few articles on the subject i see that we certainly need to improve the original set up, cheers
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kiwipom PM sent.
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I've had the Bunn breather kit on my B33 for some time and it works a treat.
I always wondered how to fit it to the A10 and now I know*smiley4*
Thanks for the post
S
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Well I think Otto has his question answered, and at the risk of going off topic, I remember seeing that the standard timed/rotary breather could be modded to work better, by elongating the hole in it? Ive done a search but not found the details on this forum, does anyone know where the post is with the details of the mod?
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?
Going back to the Bunn breather, a quick search reveals this a contraversial and much discussed topic for the other brands like norton triumph etc, another what oil is best what tyres are best sort of topic, here's a sample link which mentions the use of other valves from brake servos and xs650's
http://www.nortonownersclub.org/noc-chat/technical4-commando-forum/342798656/view
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G'day all.
Well the Bunn Breather is no more *ex*.
Mr Bunn sold the business/patents over a year ago and no longer has an interest in it.
From what I gather the new owner has shelved it. I will endevour to find out the new owners particulars in the hope that with enough inquires he may decide to commence production.
A friend had been working on a reed valve set up that tested as good as the Bunn. Watch this space.
Cheers
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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"
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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
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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.
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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
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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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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.
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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:
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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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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
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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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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
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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.
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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.
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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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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?
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/ (http://www.carcraft.com/techarticles/ccrp_9903_moroso_vacuum_pump_test/)
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?
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Trevor, your preaching to the converted. I KNOW it works, and works well.
Yes TT, we Aussies do have a different sort of sense of humor. The one that comes to mind is "you can lead a horse to water but you can't make it drink". I have one fitted to my cafe and wish I had more kits for my other bikes. I noticed the difference the moment I fitted it by having to back off the idle. Throttle response is much quicker and less oil leaks.
Lets just agree to disagree.
Cheers
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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.
Well he and the engineering school at the University of Auckland where the latter work was done and a couple of graduate thesis would all have to be wrong as well.
Please do not tell HD as they modified their engines and AFAIK rex is still getting royalties for that work.
Have a look under the hood of most Mitsubishi's.
At the rear of the engine in the rocker cover is a pipe from 1/2 to 3/4 on latter models which is plumbed into the air cleaner.
This is the fresh filtered air inlet.
Near the distributor is another line usually 1/2 with a one way valve in it which goes to the carburettor or to the engine side of the butterfly on fuel injected engines.
This is the crancase exhaust
Clean air in , dirty air out.
So if Mitsubishi went to this extent on a partially balanced engine pumping system, are they just superstitious ?
They are however not 360 deg engines like a single or Pommie twin so the flow characteristics are totally different and they can get away without a valve on the intake.
When Phil Irvine developed the Repco Brabham "Yella Terra" engine one of the things he did was to add a fresh air intake and a valve regulated exhaust.
GMH fitted this engine ( minus the big cam & domed pistons ) to the 1966 range of cars.
The full Yella Terra kit came with a new PCV valve and rocker air inlet designed to work properly at the higher revs that these engine did comparred to the standard red series engines.
I know this one as I fitted a head without the modified breathers and it was as smokey as hell under full throttle till I got the right breathers on it.
Oh and Phil did this after he had a stint at Chamberlan Tractors where he doubled the Hp of their entire range ( both petrol & deisel ) and these all got fitted with flow through crank case ventilation as part of the upgrade.
Now perhaps this was because we have high energy air down here comparred to your lazy fog up there, but some how I think not.
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Interesting stuff, thanks.
I can see how a through flow of air might clear nasty gases away and that must keep the oil and cases cleaner, to some extent. I suppose the inlet is restrictive, to maintain depression in the crankcase?
I wouldn't set much store by what modern car makers do. They have emissions priorities.
My own old bike has no oil seal on the drive end of the crankshaft, so I don't expect much air would come in through an inlet on the rocker cover. I've driven a few miles with a screw-on rocker cap missing and didn't notice any better performance or throttle response.
There is an oil seal on the timing end of the crankshaft and the acids and gases have failed miserably to destroy it, over many years.
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Here's a rocker cover, into which clean fresh air passes, in a cold damp climate.
(https://www.a7a10.net/forum/proxy.php?request=http%3A%2F%2Fi257.photobucket.com%2Falbums%2Fhh236%2Ftritonthrasher%2Fimagejpg1_zps22279d9a.jpg&hash=5ea2d2bc2c0314bd2b204d791dd41c22bb677291) (http://s257.photobucket.com/user/tritonthrasher/media/imagejpg1_zps22279d9a.jpg.html)
It suddenly occurs to me that I have not looked inside a car rocker cover since the 1980s. Motoring is not what it used to be.
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OK folks; I have now got one of the original kits for the T140, and will adapt this to suit the A10. At least the valves are the right ones. Thanks for all input.
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GMH fitted this engine ( minus the big cam & domed pistons ) to the 1966 range of cars.
The full Yella Terra kit came with a new PCV valve and rocker air inlet designed to work properly at the higher revs that these engine did comparred to the standard red series engines.
Wow- then that was likely in the Brabham (RIP Jack) Toranas too, I think the only one I saw was parked out front of my aunts' house in Melbourne about then.....! *eek*
Thanks for all the input guys
I had thought about this while rebuilding mine, so might also work towards similar mod... sometime
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Not too sure about that Brabham torana, Dutch.
My mate had one. It had a small 4 cylinder engine that wouldn't pull the skin off a custard.
It did have a racing stripe though. woo hoo.
Don't think that's the motor Trev is talking about. I'm surprised Jack 'rip' put his name on such a piece of sh!t.
cheers
oops, hope you're not passionate about them.
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Haha Yep Olev, I'm hearin' yea, would say it put the tard in custard- the one I saw was (custurd) yellow with a black stripe maybe your mates, don't imagine they made many- but if any still exist I'm sure it'd be a collectable (but you wouldn't tell anyone...!!)
Well that's that Yella Terra done and dusted...! *work* *beer*
Related, but not Bunn or engine Primary case- As an experiment the other day I fitted an old finned inspection/ filler cover to the primary so I could undo it easy when hot, to allow hot (expanded) air out to maybe alleviate pressure/oil leakage...? Will have to see if it makes a difference- just a thought
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Here is my set up.
1: intake to front tappet cover. Nice clean cool air going in at the hottest spot of the motor.
2: exit bad air out normal exit point. Piped to oil tank. Or to atmosphere if wanted.
3: bad air enters oil tank. A std tank could be modified.
4: bad air and oil fumes exit oil tank.
5: exit to atmosphere.
The only internal mod was to cut the timed breather off at the holes so the ports are always open.
No problems like blown seals. Less oil leaks. Quicker revving. You get used to the sound of the valves.
Cheers
I run bunn breathers on Bender and have adopted the opposite approach to Muskrat *eek* although otherwise comparable. I vent to a breather bottle on the sidecar deck
My fresh air comes in the original breather and fresh is vented out the top front rocker box. My philosophy for the 10cents its worth is that I want the fumes being blown topside not down through the engine as my engine fumes are carrying methanol, which I don't want dwelling in the bottom end where they can encourage corrosion.
I think the bunn breathers are ideal for any racing application, but probably unnecessary for a plodder.
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Not too sure about that Brabham torana, Dutch.
My mate had one. It had a small 4 cylinder engine that wouldn't pull the skin off a custard.
It did have a racing stripe though. woo hoo.
Don't think that's the motor Trev is talking about. I'm surprised Jack 'rip' put his name on such a piece of sh!t.
cheers
oops, hope you're not passionate about them.
The Repco Brabham ran what became the Holden red motor which was superceeded twice if not 3 times before the Torana saw the light of day.
Despite the bull shit that is being spread every where the deal was Repco footed the bill for the car ( if not all , a good lump of it ) in return for the technology and endorsements from Jack.
After Jack did the deed Repco released the engine pack in drips & drabs as did Ford with the Moffat ( phase I, II & III uprades ) Falcon motor.
These were marketed as Yella Terra, starting with just the cam ( useless ), head with cam, head cam & extractors, and full kit head cam coil distributor extractors induction tube & breather.
I am not quite sure if the "red" motor came before or after the Repco Brabham and Phil Irvine is uncharasticlly vague about the exact timing apart from the fact he was commissioned to work on the old Holden "Grey" motor ( 138 from memory ) and his work principally turned it into the "red" series ( 149 & 176 ?).
Repco continued to offer the hot up kits for the reds and for the blue series that followed.
Cerdit where credit is due, Jack was a really really good driver, but that Repco Brabham was such a good car it was around for nearly 20 years and was winning for at least 10 of them without Jack in the hot seat.
As for lending his name to the Torana, Jack was never one to turn down a job or say no to a cheque.
He was the "named front man" for the bunch of "criminals" who milked the state government mercilessly building the original white elephant called Eastern Creek Raceway.
Which from memory was a quick & dirty land grab from the bod who got framed for the Hilton bombing ( his name & the sect name eludes me at the moment ).
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Just a quick heads up.
It appears that there wil be a limited production run of the breather kits very soon for the US distributor only.
So if you want one put an order in now.
Looks like there might be a new manufacturer early in the new year, solicitors pending.
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Just a quick heads up.
It appears that there wil be a limited production run of the breather kits very soon for the US distributor only.
So if you want one put an order in now.
Looks like there might be a new manufacturer early in the new year, solicitors pending.
Trevor,
do you have any contact details for the distributor?
Cheers
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British Cycle Supply Company