Author Topic: crankcase pressure etc  (Read 6048 times)

Offline BSA_54A10

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Re: crankcase pressure etc
« Reply #60 on: 14.04. 2019 13:17 »
Quote
This all has been a very interesting topic and read it front to back.  It seems topical and resurges in interest often with different makes and models.  Some years back I worked a spell on a bike backlog for a local shop and they carried a number of bikes modern and vintage.  The owner was very interested in the BUNN Breather issue for some of the modern Enfields as we built hot rodded versions for some customers.  People tend to get tunnel vision and not look beyond their specific make and model.  At that time I amassed a huge amount of discussions and tech materials from a wide range of sources and shared it with the brain trust at that shop.
We concluded that the BUNN breather had merits but anyone could make their own versions and I suspect thats what did in the supplier.

The plumbing has been known for decades.
The trick was to find the right material for the valve that would not resonate anywhere in the frequency of the engine pulses.
Rex was a chemical engineer and eventually found a material that worked.
A sheet of it was a hock your house type price so he then hunted out users of the material , bought their scrap & hand cut all the valves from that in order to keep the price down.
Rex has a shortish attention span so after a while he was looking for a buyer but there simply was not the interest so he stopped making them and went into movie making producing 3 doccos and writing another book which includes everything he found out with the exception of the valve material.
Yes there are thousands of check valves out there.Rex and eventually the University of Auckland tested each & every valve available at the time but none worked over the entire rev range 1000 rpm to 10,000 rpm, temperature range & volume range
Some worked at low speeds & some worked at high speeds but none worked at all speeds except his.
What Rex failed to take into account was that while he wanted & was willing to pay for perfection the average British bike rider is way too cheap to pay $ 40 for his valve when they could go the el-cheapo car parts & buy a PCV valve for $ 3.95 plus 4 foot of PVC tube and that is exactly what happened .

Everything in the kit was unique to the kit
The valve , the thickness, density & size of the tubing were all specially made so they worked together.
All the current knowledge about engine exhaust went into the kits which is why they were supplied with very specific instructions about tube length for different bikes.
The kit of the B31/33 does not work on an A10 right out of the box and visa - versa.

Even the book he wrote with the results of 15 years of research never covered publishing costs.
Bike Beesa
Trevor

Offline berger

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Re: crankcase pressure etc
« Reply #61 on: 14.04. 2019 17:06 »
does anyone know if a reed valve would work? *dunno2*

Offline chaterlea25

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Re: crankcase pressure etc
« Reply #62 on: 14.04. 2019 21:31 »
Hi Berger,
Quote
does anyone know if a reed valve would work

They are fitted on XS 650 Yam's and I have read of people using them on their Brit twins

John
1961 Super Rocket
1963 RGS (ongoing)

Offline muskrat

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Offline berger

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Re: crankcase pressure etc
« Reply #64 on: 14.04. 2019 22:24 »
 I have not been to the PUB! o yeah musky its all coming back to me now, brain wouldn't go ---cheers for the link.  [again I think *eek* *conf2*] musky and john to the rescue *beer*

Offline BSA_54A10

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Re: crankcase pressure etc
« Reply #65 on: 15.04. 2019 00:08 »
Same problem.
Valves resonate so they get set to where they are most needed for that application.
Also the size of the holes are important
A small hole will have high velocity gas coming out which is good for opening a sprung valve
A big hole has low speed gas which is good for a flapper valve.
At last 50 people can tell you that the M20's breather works perfectly at any speed up to about 1/3rd throttle.
Engine is nice & oil tight (ish )
But WFO for any more than 3 or 4 minutes and all behind me are waterproofed.
The std A 10 timed breather is good to around 3000 rpm then it gets progressively more out of sync with the gas flows till it ends up backwards at 7000 rpm
Between 3 k & 7 k is generally when the rocker box leak becomes chronic .
This is because the crankcase fume has weight so the movement of the gas under the piston lags piston movement but the breather remains in sync with the movement of the pistons so it is out of time with the movement of the gas.
Then there is the resonance of the exhaust tube, just the same as the engines exhaust pipe it can end at a pulse node which will prevent the movement of oil .
Bike Beesa
Trevor

Offline muskrat

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Re: crankcase pressure etc
« Reply #66 on: 15.04. 2019 00:17 »
 *pull hair out*
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
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Muskys Plunger A7

Offline t20racerman

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Re: crankcase pressure etc
« Reply #67 on: 15.04. 2019 09:13 »
The std A 10 timed breather is good to around 3000 rpm then it gets progressively more out of sync with the gas flows till it ends up backwards at 7000 rpm
Between 3 k & 7 k is generally when the rocker box leak becomes chronic .

This is exactly what I found, and why I fitted the Bunn valves to my A10. I could ride round all day up to about 3400rpm without much more than a gentle weep at worst out of the rocker cover - hold it at about 3800-4000rpm though on a dual carriageway or fast road, and it turned into an oil pump! If I slowed back down, the leak stopped. SO frustrating
I can now run it at 3800-4000rpm for long distances (75-80mph) without a problem thanks to the Bunn valves. its such a shame they aren't being made any more. :-(
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!"

Offline berger

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Re: crankcase pressure etc
« Reply #68 on: 15.04. 2019 11:20 »
ok chaps so put it to me in simple terms, is the yam 650 breather any good for  my 500 that will be revving [ hopefully] between 1000 and 6500 max, [6500 on a mental day] or do I need this non obtainium chocolate BUN *dunno* *help*

Offline muskrat

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Re: crankcase pressure etc
« Reply #69 on: 15.04. 2019 20:46 »
G'day berger.
Yes, one in one out.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
Muskys Plunger A7

Offline berger

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Re: crankcase pressure etc
« Reply #70 on: 16.04. 2019 12:38 »
I went to the pub *countdown* musky you are a star, you told me that ages ago *whistle*--- I remember now you've said it again. brain needs a talking to *bash*