Reed Valve piping

Cant recall this being discussed before. Fitted my own reed valve block to the left lower crankcase, I made mine with a 1/2" outlet, now I dont feel comfortable connecting that to the 3/8" pipe at the top of the tank, a bit restrictive I think. I guess the best option would be to connect it to a catch tank which vents to the atmosphere. any idea how much oil is sent back to the tank via this reed valve setup?
your thoughts.....

Comnoz has posted videos showing that this breather method can shift huge amounts of oil with a 'wetted' sump. When all running properly, mine appears to put very little oil through the breather. But if you vent it to atmosphere, I guess you'd have big puddles on the floor after a cold start up from a longish stand.

I have Jim's reed valve on a Rickman, oil in frame.

Jim was very clear that I should not vent this to atmosphere, for the reasons Nigel mentions. This made life a little more complex with the Rickman since they originally did not return the breather pipe to the 'tank'.

The outlet from Jim's breather is 3/8" OD and the return to my Rickman frame is also 3/8" OD. To cover concerns about returning oil to the tank completely unfiltered I have fitted a screen filter designed for turbo oil feed filtering on cars, in line with the 3/8" hose. Fittings are are 6mm internal bore! I am pretty sure there is no concern with restriction and there is clearly, positive pressure in the tank, which makes sense if you have achieved negative pressure in the crankcases!

I do have the 'tank' vents (2 off at 1/4") running to a 0.5 litre catch tank and some oil does collect in this. The amount accumulated seems to vary with the amount of oil I put in the frame, last time 4 track sessions produced around 150ml. The frame will take 6 1/2 (imperial) pints or more, but it seems better with 5 to 5 1/2 pints, which is plenty. I don't find the tank breathing unusual, since this is a race bike application and is revving hard most of the time, other breather arrangements I have used racing have always produced something in the catch tank, often much more that this,maybe 0.5 litre in 4 track sessions.

Hi Madass140.
I had this concern on my Combat engine that had a front of cases oil pickup. The oil would build up at the rear of cases and be forced through the breather at high revs/speed. I have recently moved the oil pickup to the rear of the cases to reduce this problem, I hope.
To find out how your bike fares, perhaps plug the breather hose into say a 2 litre cordial bottle without a cap and go for a ride - if just fumes, ok.
If litres, you will need a way to return the (unfiltered) oil back to the tank from the catchcan. Similarly, if your cases wet sump then you will need this same system.
The hot air blasting into the oil tank was another concern overcome by using a catchcan.
Ta.

Don

As an aerodynamicist, I assure you the reduction of 1/2 inch tube to 3/8 is of little significance. Don't worry, just do it, and be happy.

Slick

Reed valve to oil tank. Then make sure the oil tank can breathe too. I run my oil tank breather to the air box and I've never seen oil there.

The volume of the expulsion of air from the crankcase is of little concern. The issue is keeping air from going back in on the upstrokes. Even at high RPM's, it is a cyclic thing rather than a volume thing. The original breather reduced to 3/8 from 1/2. Not a problem

I think when people hear "breather", they miss the true concept, nature, and purpose of these reed devices.

As our Texas turd kicker aerodynamicis says, tube size is way over kill for the volumes being moved and this shade tree adds that slightly smaller tubing moves the slight slugs of pressure a bit faster denser to work flappers a bit better. Not likely acceptable here but coming from a fast boat background thinking of just putting a duck bill scupper valve on end o oil tank vent tube. MIght even make a whoppie cushion sound on start ups. Ludwig might appreciate its features.

The Combat so called breather and bottom of the crankcases was a complete disaster but by that time Norton or whatever they were called had no real Engineers left. When NVT went to the wall in a certain cellar in Birmingham one could buy brand new Combat crankcases for £20 a pair....new boxed RH6S heads being £40 .... new disc brake front wheels complete with new Dunlop rims £20 each etc etc..Happy days for rich Norton owners who were allowed into such places......
Personally I refused to use my crankcases as a compressor blowing out air as the pistons came down and then sucking it back in as the pistons went back up ...as the idiots at Triumph later did it with tht stupid idea of breathing into the chain case...DONE so a Service Manager told me because opf the number of bikes coming into the factory for servicing with damn nigh solid primary chains because the owners were incapable of ensuring the correct oil level in the chain case!! Naturally I will not mention all those Commando owners who overfill their primary oil bath chain case by filling to the oil level plug instead of reading the manuals instruction 'under no circumstances allow more than 7 fl oz (200cc) of oil in primary case'. Section K8 in the 750/850 Commando Workshop Manual. Not that the young ever read such things as I remember it!!
BMW did a bit (Bit of ha ha they spent a lot of time and money so I heard) of research on crankcase breathing many years ago and came up with a proper reed valve. Personally I ran the crank breather from the top face of the timing chest vertically back to the oil tank and placed the reed valve in the top of the tank. The only thing that ever came out of it was air / oil mist and then initially only a few puffs as the reed valve worked till crankcase pressure settled down to bugger all .... till blow bye on the rings increased crankcase pressure again and the reed valve gave the occasional puff to compensate. JUST to be on the safe e side for racing the valve vented into a small bottle but I never found any significant oil in it.
Of course Norton twins originally employed a timed breather at the end of the camshaft that opened as the pistons came down and closed as they went back up..........
An interesting bit of reading is the section on crankcase breathing in the book 'Tuning BL's A - Series Engine' by David Vizard.
Oh and a very old Triumph breather system worked very well..run the breathers back to the oil tank and shove a tiny hole in the filler cap. As the pistons come down creating compression it is forced out through the small hole but as the pistons go up very little air at atmospheric pressure outside can be sucked back in and after a few rpm it all settles down very nicely to, so I was told, about 1 lb above atmospheric.......That should solve any engine leak problems.......

I adapted the Yamaha 650 reed valve to bolt directly to my crankcase and it's line also gets reduced at the oil tank. After enough time has passed to wet sump, I kick it over a few times with key off and watch the oil dump into the tank from the reed valve. When I start the engine, the oil cap better be on because that reed valve immediately finishes the job of drying the sump. I have never noticed any issue that might relate to the hose diameter reduction.