Additional or alternative engine breather

piggywig

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Non-VOC Member
More Breathing.

Clevtrev,
Ref. your cryptic remark : (Also remember the more you breathe, the less likely your return oil side will return oil.)
I think it would be of great benefit to the many owners who have tinkered/modified the standard breather to hear of any possible downside in doing so, and less returning oil sounds rather ominous!
I would certainly like to hear more-- please.
Regards,Col.
 

John Appleton

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VOC Member
I think it would be of great benefit to the many owners who have tinkered/modified the standard breather to hear of any possible downside in doing so, and less returning oil sounds rather ominous!
I would certainly like to hear more-- please.
Regards,Col.[/QUOTE]

I am sure trevor is trying to get you all to put your thinking caps on before modifying anything with more enthusiasm than skill. Let us consider the conditions in the crankcases, and there are three possible variations on the pressures involved.
The first is pressure too high. Possible causes are blowpast at the piston rings or mistimed breather.
The second is pressure too low ie a partial vacuum. Possible cause mistimed breather.
The third is neutral ( ie atmospheric)
If the pressure is too high it will lead to oil leaks at the weaker sealing faces, but the scavenge pump will have an easy time as the pressure will help it in its designed task.
If the pressure is too low (partial vacuum) there will be no oil leaks, but the scavenge pump will have to overcome this depression before it can return any oil to the tank. In an extreme case it is conceivable that it will not work at all !
If the pressure is neutral (ie atmospheric) it would suggest that the breather is sucking and blowing leading to large quantities of dirt entering the crankcasing unless an efficient filtration system is employed.
There are many other pros and cons for each condition described, but these will give you the idea.
I have looked at various solutions that people have come up with and can see shortcomings in some of them . The most obvious of these concerns the breathers which are vented through either the valve spring or push rod caps. The valve gear depends on some of its oil running back down the pushrod tubes, and the last thing it needs are great gouts of displaced air pushing it back to where it came from. this displaced air is also being forced to pick up some of this oil and carry it with it out through the breather pipe.
The elephant trunk breather seems to me to be one of the better ideas, but to my eye is ugly.
I am using a home brewed system which consists of a chamber , fitted in place of the ATD cover, which is separated from the timing chest by a poppet valve held closed by a very light spring. The fumes which pass this valve are automatically deflected onto the walls of the chamber which has the effect of separating the oil content. In the bottom of the chamber is a 3mm hole through which the oil is sucked back into the engine as the pistons rise. The fumes pass out of the chamber through a 1/2inch o/d tube, the inlet of which is at the highest point of the chamber and this tube exits the chamber at the bottom and down under the engine through a convenient hole in the front propstand plate.
I have retained the original breather and , by virtue of the poppet valve, the extra breather can be considered as an auxhillary which only operates when the pressure rises to an unacceptable level.
It works.
John
 

clevtrev

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VOC Member
So John is pointing you in the right direction. Consider the operation of the pump. At 1000RPM Engine speed the pump will operate a little over one second between pulses, that means oil has to flow through an opening 5/16"dia over a short distance to fill the pump, this is the largest opening time , the faster you now go, decreases the opening time. So you think oil will fill that opening in that time ? No, the pump will cavitate, without some help.
Try a little experiment, only those with breathers other than standard need bother. Take a normal ride, say for 10 miles, drain the sump and measure, then another 10 miles with a speed not exceeding 40mph. measure amount of oil in sump. I will guarantee that the oil level will have risen. I should say put the sump oil back in before the second ride.
Discuss.
 

peterg

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Non-VOC Member
Howdy Trevor,

So extending this scenario of compromised scavenge through lack of positive crankcase pressure assistance: if one rides far enough on a PCV they will gradually wet sump and possibly hydraulic if not emptying their UFM first?
 

Bill Thomas

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VOC Member
Evening All,
After 44 Years of over reving Vins, 17 of them racing, The only trouble I've had with oil returning was too much !!.
Many racers find with the 2 start oil pump as soon as the revs go up oil squirts out the breather hole in the filler cap. I soon went back to the standard pump. My Special twin once reved to 6,500 on standard gearing
on a flying kilo'.
If you think about every squirt of oil going to the right place at the right time you will not go far.
I say "Suck It And See".
All The Best Bill.
 

timetraveller

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VOC Member
One thing which I think I have mentioned before but not on this thread is that fitting an open atmospheric breather, i.e. 'D' type, in conjunction with a timed breather cannot be a good idea. The whole point of the timed breather is to let air out when the pistons are descending and to stop air going in when the pistons are ascending. Guess what will happen if you have an open 'D' type breather when the pistons are going up! That's right. Air will get sucked in meaning that there is more to expel when the pistons come down next time. One or the other chaps but not both.
 

john998

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VOC Member
Breather

Timetraveller makes a good point, you can have a timed breather or an open one, both together can cause the open one to pull in dust and grit.
Aeons ago I fitted an open breather on the primary case, the result was a gritty sludge in the bottom of the case.
My set up now is a form of elephants trunk made up in stainless steel that Ivan Caffery used to supply. It has a nylon ball non return valve that is a little noisy but it cut the oil consumption by 50%.
Not sure why some folk call the valve a PCV, I think they are more correctly called non return valves.
As far as negative crankcase pressure causing oil return problems go, I like Bill Thomas have not had any trouble. The potential negative pressure if you are very lucky is only a few millibars, and is unlikely to be achieved on most engines. John.
 

clevtrev

Well Known and Active Forum User
VOC Member
Howdy Trevor,

So extending this scenario of compromised scavenge through lack of positive crankcase pressure assistance: if one rides far enough on a PCV they will gradually wet sump and possibly hydraulic if not emptying their UFM first?
As I see it only extended running at low RPM. There must be a point when the breather ceases to operate as such. Consider the timed breather, as I said before, it opens approx each second at 1000RPM. At 4000RPM it opens 66 times a second ! The constant is the volume of air compressed but the opening time is virtually nil. So what happens then ?
 

piggywig

Well Known and Active Forum User
Non-VOC Member
Time to evaluate.

My purpose in initially starting this thread was to tap the collective wisdom of the V.O.C. before carrying out alterations to the breathing, intending to let the pistons/bores bed in first which should improve breather pipe ejection of oil, now collected in a conveniently located catch tin instead of on the rear tyre. Plenty of info to go on so far, albeit some conflicting, but we are getting something of an education on the questions involved in crankcase breathing, which will help in deciding on a suitable breather set-up, standard or otherwise.
Thanks to all contributors.:rolleyes:

Col.
 

Bill Thomas

Well Known and Active Forum User
VOC Member
Hello Col,
If you use a big pipe with an oil separator you don't need a catch tin.
In the 70s Hillman Cars used a round plastic separator which came off the air cleaner box. The IN and the OUT are offset with a bit of mesh between. I know they don't look good but I gave up with standard breather years ago. On my Comet I use a D valve cap on the EX tappet cap, short right angle pipe ,separator,then a short right angle pipe which tucks into the front of the petrol tank.
My Lightning rep' has an alloy pipe welded to the Mag' inspection cover and up to the same place. As long as the outlet pipe does not go down I have found you only get a bit of oil mist.
Good luck Bill.
 
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