Assuming we are talking Comet/Meteor here. The sleeve E217 is an interference fit in the crankcase. it is 1/2" o.d. The recess where it sits on the outside of the crankcase is bored 3/4". You should be able to get a 1/4"or 3/8" BSP right-angled elbow to adapt to the spot by machining a simple sleeve. Anchor in place by a bracket from the F120 nut plate.You then get some tube and a couple of really cheap plastic one-way ball valves from a fish tank supplier, or on ebay from Hong Kong. run the tube as high up as you can. This is easy to do when the machine is being built, but a bugger when it is together. The Twin's sleeve is already threaded 1/4" BSP but I don't know if there is room for this wheeze. Note; Measurements need checking, as I did them with a vernier and the spot was inaccessible.
Terry Prince Top End Kit
- Thread starter davidd
- Start date
Sadly not a good idea as ball valves tend to only work at very low speeds as they go into resonance and not seat due to their high mass and low stiffness. Best to use a reed-valve system like two-stroke inlet reeds if you're serious on properly ventilating a crankcase using pressure actuation.
Probably correct as a counsel of perfection, but it worked fine for 20 years on my Guzzi. Eventual failure was only due to the cheap buggers using non-stainless ball and spring. The thing I've got against reed valves and baffle tubes is merely a reaction to egregious extrusions. On the Comet on Steroids I made a non-standard banjo from the standard outlet point, then a car in-line PCV valve, 20mm i.d. clear plastic tube upwards and rearwards to a catch tank mounted on the F106 casting. The catch tank is vented at the top and has a drain tap and tube onto the chain, which I open and close as the whimsy takes me. Even if the ball sticks open the large diameter upward pipe is better than the series "D" set-up.
All good chaps and everyone to their own but my comments are based on actual testing. If you were to use a high speed camera on your ball valves you would see them remain unseated above 2,000 to 3,000 engine rpm so instead of any sort of valve action to maintain sub-atmospheric crankcase pressure you're relying on air viscous drag forces which is highly ineffective. Under this condition a low air-pressure transducer connected to your crankcase will show nice pressure spikes. Still - if the oil stays in all good then? 
I seem to remember some correspondence on this which discussed an Enfield one way valve. It was just a moulded tube with a flattened end which, presumably, could open and close at high speed. I think these are referred to as 'duck bill valves in some applications and as 'joker valves' in the types of hand pumped toilet one gets on sailing boats. Has someone found out that these do not work on Vincents and if so could they let us know what is wrong?
Set up you original timed breather as advised by Irving in "tuning for speed" and you will have no further breather issues. No need for ANY of the so called 'solutions'.
Now if you have piston blow-by thats pressurising your cases thats a totally seperate problem - NOTHING to do with the breather. Fix that first!!!
Ba Ba
Young John says he tried 20 different PCV valves before he found what was good for his bike, 10 out of 10 for effort !!. Cheers Bill.
I fitted one of those enfield duck bill valves to the standard breather tube on my series A Comet. It works great. Remember though the breather on a series A is just an open pipe from the rocker area of the cylinder head and is not a timed breather.