Author Topic: A working Bunn valve breather system on my A10.  (Read 641 times)

Offline t20racerman

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Hi all

The topic of crankcase pressure and the BSA timed breather system has been discussed quite a lot on this site in the past (eg here - https://www.a7a10.net/forum/index.php?topic=721.0 ) and I joined in a few of these discussions as I was interested in fitting a Bunn valve (one-way flow) system to my A10. I did eventually do this to my bike, but I had to take it off the road shortly afterwards due to a few unrelated problems including a failing gearbox and (sadly!) it was off the road for nearly 18 months...

Anyway, its back on the road, running lovely, and that inspired me to make a YouTube video of what I did and how I did it for those who are interested. (The video is of the latest set-up as I've improved/changed it twice)

You can find it here:
https://www.youtube.com/watch?v=P1gGEYJd-A0

Hope you find it interesting.

If you want to see the bike being taken for a thrash through the countryside, here's another video that I did some time back.
https://www.youtube.com/watch?v=Wg8_lj2q4ac&t=1s

All the best

Adrian

1961 A10 - somewhat modified :-)
1980 TZ350 - lunatic Classic Race machine
1967 T20 Suzuki - heavily modified Classic Racer
1967 T20 Suzuki - pretty standard road bike
2007 KTM 660 SMC - fast and furious supermoto
Triumph 675 Speed triple
Ossa 250 and yet another T20 racer in bits both being built up

"If I had all the money back that I've spent on motorcycles... I'd spend it all on motorcycles!"

Online muskrat

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Re: A working Bunn valve breather system on my A10.
« Reply #1 on: 11.04. 2019 09:57 »
G'day Adrian.
That looks familiar.
Shame their unobtainable now.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Offline BSA_54A10

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Re: A working Bunn valve breather system on my A10.
« Reply #2 on: 11.04. 2019 10:24 »
G'day Adrian.
That looks familiar.
Shame their unobtainable now.
Cheers

The whole kit & cabbodle is for sale if you want to make Rex an offer
You could sell them as Musky-Bunns, I can see the packaging right now.
Bike Beesa
Trevor

Offline t20racerman

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Re: A working Bunn valve breather system on my A10.
« Reply #3 on: 11.04. 2019 10:33 »
Hi muskrat

Yes, you were one of the original commentators that piqued my interest in Bunn valves! So thanks for that :-)

Although the original Bunn valves aren't being made any more, there are numerous similar products on the market that would be just as good. Search for 'check valves'. Here's a good site:

http://www.smartproducts.com/check_valves_series_100_cartridge_specialty.php

Plenty of others too. Industry use these a lot.

Cheers
Adrian
1961 A10 - somewhat modified :-)
1980 TZ350 - lunatic Classic Race machine
1967 T20 Suzuki - heavily modified Classic Racer
1967 T20 Suzuki - pretty standard road bike
2007 KTM 660 SMC - fast and furious supermoto
Triumph 675 Speed triple
Ossa 250 and yet another T20 racer in bits both being built up

"If I had all the money back that I've spent on motorcycles... I'd spend it all on motorcycles!"

Online berger

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Re: A working Bunn valve breather system on my A10.
« Reply #4 on: 11.04. 2019 11:09 »
T20 racerman what size did you tap the crankcase and what is the bore of the fitting cheers, at the moment mine is tapped 3/8 whit cheers

Offline t20racerman

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Re: A working Bunn valve breather system on my A10.
« Reply #5 on: 11.04. 2019 12:39 »
T20 racerman what size did you tap the crankcase and what is the bore of the fitting cheers, at the moment mine is tapped 3/8 whit cheers

I really don't remember the thread size - I originally tapped it back in the early 90s when my bores were badly worn and the bike was blowing out a lot of oil - I did it to put an oil collection tube and container on!

Re the hole in the middle, again, my memory eludes me. I reprofiled the outer end, and then re-drilled it recently to make the hole bigger, and went as big as I dared before making the walls too thin. 7.5mm rings a bell. As wide as possible seems the way to go.
1961 A10 - somewhat modified :-)
1980 TZ350 - lunatic Classic Race machine
1967 T20 Suzuki - heavily modified Classic Racer
1967 T20 Suzuki - pretty standard road bike
2007 KTM 660 SMC - fast and furious supermoto
Triumph 675 Speed triple
Ossa 250 and yet another T20 racer in bits both being built up

"If I had all the money back that I've spent on motorcycles... I'd spend it all on motorcycles!"

Online berger

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Re: A working Bunn valve breather system on my A10.
« Reply #6 on: 11.04. 2019 12:59 »
ok racer man the hole in crank case is near to 8mm and my tube outlet 7mm , I will be looking into this before I build it  up  cheers

Online chaterlea25

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Re: A working Bunn valve breather system on my A10.
« Reply #7 on: 11.04. 2019 19:00 »
Hi All,
Some years ago I fitted a Bunn breather to an AMC 650 twin, they originally a flap valve breathing into the primary case

I fitted the inlet to the rocker box and an outlet stub welded into the timing cover
It works very well  *smile*  Rather than oil gathering in the bottle water vapour condenses in there and needs emptying out every so often

On another Notrun that had oiling problems I tried a catch bottle as well, it filled with snot like emulsion *eek*

From those experiences I think piping the breather back to the oil tank is a bad idea  *????* *????*

John
1961 Super Rocket
1963 RGS (ongoing)

Offline t20racerman

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Re: A working Bunn valve breather system on my A10.
« Reply #8 on: 11.04. 2019 19:50 »
Hi All,
Some years ago I fitted a Bunn breather to an AMC 650 twin, they originally a flap valve breathing into the primary case

I fitted the inlet to the rocker box and an outlet stub welded into the timing cover
It works very well  *smile*  Rather than oil gathering in the bottle water vapour condenses in there and needs emptying out every so often

On another Notrun that had oiling problems I tried a catch bottle as well, it filled with snot like emulsion *eek*

From those experiences I think piping the breather back to the oil tank is a bad idea  *????* *????*

John

A fair point, and I have noticed some condensation coming out the breather - but only a very tiny amount. It's something I'll keep in mind, but when I originally routed the outlet pipe down towards the swing arm, rather than up to the oil tank, I did get a lot of oily vapour blowing out and it made a right mess on a long run (no catch bottle originally...). Now its going upwards, there will be a tendency for any oily 'mayonnaise' that was going to form to stay engine side and hence get hot and so not last for long.

Also, I tend to use the A10 for decent distance rides, and ridden quite hard too, so it usually gets pretty hot when run, and any condensation should be disposed of via the breather pipe, rather than contaminating the oil. Thanks for your thoughts, and I'll monitor the situation, but everything is working well, and as I'd hoped for, at present. Hopefully it will remain so!  *smile*

Adrian

Edit: Another thought - collecting condensation and a little oil vapour in a small cold collecting bottle would definitely encourage the emulsion you saw wouldn't it? Whereas a hot oil tank wouldn't?
1961 A10 - somewhat modified :-)
1980 TZ350 - lunatic Classic Race machine
1967 T20 Suzuki - heavily modified Classic Racer
1967 T20 Suzuki - pretty standard road bike
2007 KTM 660 SMC - fast and furious supermoto
Triumph 675 Speed triple
Ossa 250 and yet another T20 racer in bits both being built up

"If I had all the money back that I've spent on motorcycles... I'd spend it all on motorcycles!"

Online chaterlea25

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Re: A working Bunn valve breather system on my A10.
« Reply #9 on: 11.04. 2019 21:16 »
Hi T20,
The catch bottle is sited well hidden away up high beside the iol tank on the AJS, that one only shows water
The Notrun has an alloy oil tank that might cool the oil a bit?
I tried lots of permutations on the Norton with routes and places to feed the breather pipe to
including the oil tank, I had transparent tubing from the crankcase to the snot was easily visible  *eek*
(The eventual cure for it was to go back to the original 3? start oil pump gears and breathe into a bottle)

A long time ago I built a tuned engine for a BMC mini, I added a 3/4in breather into a catch bottle, it gathered water too
The engine oil stayed like new in it and none of the usual snot in the rockerbox

John
1961 Super Rocket
1963 RGS (ongoing)

Online muskrat

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Re: A working Bunn valve breather system on my A10.
« Reply #10 on: 11.04. 2019 22:16 »
G'day John.
I don't see much "snot" at all. Must be the hotter, drier weather down here. I run the breather tube to the oil tank then vent it through the Bunn to atmosphere. The "snot" is an emulsion of oil and water (humidity in the air) which evaporates out when the motor warms up. That's why I always bring a motor up to operating temp before I shut it down. Good excuse for a few laps of the block.
G'day berger.
1/4 BSP for a 3/8 hose on the inlet (front tappet cover). Drill and tap same at the outlet hole in the case.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Offline Rocket Racer

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Re: A working Bunn valve breather system on my A10.
« Reply #11 on: 12.04. 2019 00:27 »
on my methanol (very hygroscopic) a10 road rocket  which also runs a bunn set up, my catch bottle when emptied typically includes a quantity of water! presumably attracted by the methanol contamination from bore wash.
So on a race machine the bunn set up is very good for clearing water absorbing fumes.
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
New Zealand

Online ironhead

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Re: A working Bunn valve breather system on my A10.
« Reply #12 on: 12.04. 2019 01:00 »
G'day John.
I don't see much "snot" at all. Must be the hotter, drier weather down here. I run the breather tube to the oil tank then vent it through the Bunn to atmosphere. The "snot" is an emulsion of oil and water (humidity in the air) which evaporates out when the motor warms up. That's why I always bring a motor up to operating temp before I shut it down. Good excuse for a few laps of the block.
G'day berger.
1/4 BSP for a 3/8 hose on the inlet (front tappet cover). Drill and tap same at the outlet hole in the case.
Cheers

G'day Musky
You got a reverse head on that engine ? :o
SA

Offline Rocket Racer

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Re: A working Bunn valve breather system on my A10.
« Reply #13 on: 12.04. 2019 02:25 »
with methanol, my theory is I want to introduce fresh air to the bottom end and extract the contaminated air from the top end, so my exhaust rocker cover is also the outflow for my breathers. Works for me. sounds like the opposite of Musky's set up.
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
New Zealand

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Re: A working Bunn valve breather system on my A10.
« Reply #14 on: 12.04. 2019 09:44 »
Yes I have the inlet Bunn in the exhaust tappet cover with the little air filter sitting just in front of the frame down tubes. I figure that's where the cold fresh air is , cooling the hottest part of the motor.
Exit is the normal breather exit in the crank case and piped to the oil tank. The oil tank is vented through the exhaust Bunn to atmosphere.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7