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Additional or alternative engine breather

piggywig

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Non-VOC Member
In a recent posting Tom wrote of adding a breather to the front exhaust valve cap, while the series D had a breather fitted to the front inlet valve cap and a recent photo of a lightning I saw had the modified or additional breather fitted to the front inlet rocker cap. It is obviously easier to fit to the rocker cap as the top valve guide seat needs modifying (K.T.B.) in the D arrangement, so what is the best technically leaving aside aesthetics? On a C the exhaust valve cap appears to be the only place that offers plenty of room for fitting apart from the rocker caps.
My rebuilt C engine emits oil through the standard breather but if it does not improve with 'running in' then other solutions will need to be investigated. I have a quite successfully installed a neat catcher box with vent and a drain plug behind the left pillion plate to keep oil from the rear wheel, but preventing it getting there in the first place would be a better solution. Answers anyone?
I have yet to see a Vincent with a rusty rear wheel...........................
Col.
 

Howard

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VOC Member
I used the front exhaust rocker cover for a long time, without the timed breather. I think the rocker cap is a better option than the valve cap, because the path to it from the crankcase is less restricted. Seemed ok, but it did need a catch tank. I replaced it with a breather in place of the rev counter drive (never used a rev counter on the road) that was better, but still lost some oil, and it isn't as neat.

At the moment I've got the rev counter breather, but fitted with a non-return valve. I haven't done enough miles to recommend or condemn it yet.

If you look on the internet there's a breather system advertised for classic bikes, look for Bunn breather (I think) you may even find details on this forum. I don't know much about it, but it gets rave reports on it's own website (well, it would would'nt it ?).

H
 

BigEd

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VOC Member
VOC Forum Moderator
Here is my experience with my'48 Rapide, built from (what seemed like a million) battered bits that had returned from Argentina. I got it registered and back on the road last September, i.e. just over 12 months ago. I'm still getting the bugs out but having put on 10,000 miles there are hopefully not too many bugs left to sort. I used a standard timed breather set-up initially and this was pretty oily. As the new pistons and bores bedded in things improved a little.
There were/still are various weeps and drips from poor joint faces. Modern sealants have reduced these significantly.
I re-routed the breather pipe straight up and over the top of the engine and into an approximately half pint plastic catch bottle. Over two to three
hundred miles the bottle maybe collected a quarter pint of oil/watery emulsion.
The next mod was some sort of car PCV valve bought cheaply on ebay and plumbed into the rear cylinder exhaust rocker cap. Several people on list have done a similar modification. This breather was also routed to the catch bottle so that I could monitor the effect. The result is that the catch bottle now collects very little. Over the last 1500 miles it has collected perhaps two egg cups of oil/emulsion.

Summary: On my machine the PCV valve seems to have improved the breathing.
I still have the original breather operating so maybe I could try plugging this and see if this is better or worse.


In a recent posting Tom wrote of adding a breather to the front exhaust valve cap, while the series D had a breather fitted to the front inlet valve cap and a recent photo of a lightning I saw had the modified or additional breather fitted to the front inlet rocker cap. It is obviously easier to fit to the rocker cap as the top valve guide seat needs modifying (K.T.B.) in the D arrangement, so what is the best technically leaving aside aesthetics? On a C the exhaust valve cap appears to be the only place that offers plenty of room for fitting apart from the rocker caps.
My rebuilt C engine emits oil through the standard breather but if it does not improve with 'running in' then other solutions will need to be investigated. I have a quite successfully installed a neat catcher box with vent and a drain plug behind the left pillion plate to keep oil from the rear wheel, but preventing it getting there in the first place would be a better solution. Answers anyone?
I have yet to see a Vincent with a rusty rear wheel...........................
Col.

Regards,
Eddy
 

peterg

Well Known and Active Website User
Non-VOC Member
Breather: PCV

Howdy Sir,

One from the “similar modification” camp on exhaust rocker mounted PCV’s, you can view my simple solution here in our photo section.

For old hands here the Vin breather subject has been flogged for 60 years but some new members to the fold may benefit from further bleatings on the topic so bear with me for (way more than) a moment. Like shock absorbers and ATD’s, timed breathers were in their relative infancy in the mainstream as m/c manufacturers transitioned away from crankcase turbulence as a supplement to early (inadequate) positive pressure lubrication systems. The mere presence of an un-valved atmospheric breather like the “D” indicates that the makers here were more inclined to evacuate positive pressure than use it to drive atomized oil to the far reaches of the engaged volume to supplement the oil pump. So therein lies our mission. Reduce positive pressure…but for many of us without complete sealing (ie, valve stems and generator drive) not stray too far into a significant vacuum as other issues can arise.

So, some primary elements for consideration are displaced volume (at BDC) and vent velocity, the latter to be viewed as a reverse of the preferred environment to atomize fuel. You want to reduce the displaced volume over time, thereby enabling use of a smaller breather device which is porting less gases at lower velocity so the oil has a chance to drop out before being vented. By installing a PCV, you will note on engine start up a high volume of gases vented at rather high velocity but in a matter of seconds it will begin to draw down positive crankcase pressure thereby reducing volume and velocity. If mounted vertically atop your #2 exhaust rocker cap you will benefit from the pushrod tube, cap and PCV acting as a vertical standpipe to let surface tension capture the now more slowly passing mist, converting into droplets which thereafter can drain back into the sump.

The issue with the timed breather? It is just that, timed, it cannot control vacuum and pressure to the degree a PCV can, which being pulse activated is constantly on duty and can be tuned by virtue of activating spring pressure and controlled vacuum leakage. Worse, its position low nearer the source of the pressure differential – the port in the timing side case leading to the crankcase gallery – where that port, acting as venturi is atomizing oil centrifuging off your flywheels and now blown out into the timing chest at BDC. Whereas the breather sleeve may be large enough to handle some volume it is completely negated by the restrictive banjo fitting and no benefits of surface tension to capture oil mist in these high velocity gases can be realized because the line is routed immediately downward to exit.

The rap on open atmospheric breathers is that any atmosphere being ingested as the pistons rise to TDC must be re-expelled on descent to BDC so these devices have to work at the high end of displaced volume all the time to be effective and that is why bigger (and more obtrusive) is better. Admittedly by its size, an Elephant trunk is very effective at de-atomizing vented gases of oil by virtue of lowering velocity, presenting lots of capture area for surface tension to work and nearly a foot vertically to conduct this process on.


Admittedly, my two machines fitted with the above PCV and timed breather blanked off do leave a few drops after a ride because I have elected not to fit any capture device, like say a wire mesh pad inside vessel along the lines of the old vent caps on old car valve covers, but the total elimination of oil wafting out the de-compressor hole in the timing cover to liven up handling from an oily rear tire is more than payback.

 
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piggywig

Well Known and Active Website User
Non-VOC Member
Breather /PCV valve

:)Thanks to all who replied to my initial thread, and especially to Peterg for the full and detailed reason and theory behind the venting process. ( And I thought it's main job was to preserve the left side of the rear wheel to match the chain oiler that takes care of the
right!)
If the PCV valve with it's relatively small 3/8' outlet sees the the exiting air moving quite rapidly, would two be of advantage in providing double the area and perhaps not carrying precious oil away??
I have long been plagued by the "vent pipe auto oiler' ( and what Vincent owner has not?) and the hidden catch tin seemed a second best solution, together with an oil impervious garage floor finish. Now help appears to be at hand, as there are quite a number of PVC type valves suitable for motorcycles, or claimed as such.
As with all advice one can assess it's worth by carrying out a trial, evaluate the effectiveness or otherwise of the mod. and then settle on a more informed and hoped for permanent improvement, but there now seems to be a far better chance of the oil staying inside the engine.
Col.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Come on Trev, Tell us more you can't just leave it at that.
I've always used a 3/4'' big pipe and not had trouble.
All the fast lads use similar.
Such as the "Jim Smith" Engines.
Cheers Bill.
 

peterg

Well Known and Active Website User
Non-VOC Member
Howdy siir,

Two would no doubt be likely more effective depending on the characteristics of the PCV's employed. I was just looking for THE most unobtrusive, effective and quick fix... forgoing the oil entrapment device as earlier mentioned.

Speaking of unobtrusive, Earnesto's solution is hard to beat and besides capturing oil mist it is capitalizing on an equation to seek advantage. The air volume in the UFM acts to change the ratio of displaced volume (by the pistons) to engaged volume (an area within your powerplant where turbulance has access). The larger one can make engaged volume compared to displaced volume, all things being equal (gas flow within the engaged volume) the less turbulence you have to deal with.

Very nice, but a PCV over time acts to lower the amount of turbulence to be dealt and a lot easier to install than getting to the chain oiler at the UFM.
 

vin998

Well Known and Active Website User
VOC Member
VOC Forum Moderator
One thing that has always worried me about Earnesto's breather solution of connecting it to the oil tank is it's not just air and oil breathing into the tank, but also water. Look at what comes out of your breather. I put a bottle on the end of my Vincents breather pipe, and over a dry 200 miles it collected a teaspoon of emulisified oil which was floating on top of 50cc of water.
In Earnesto's breather, that water would also have been returned to the oil tank as water vapour. Modern engines run the oil hot enough so the water is evaporated off, but the oil temperature in a Vincent's oil tank is a lot lower.

You could blame it on the damp weather in the UK but the above test was on a dry run to the Severn rally. Maybe where Earnesto lives is it very dry, but you will still get a very small amount of water vapour passing the pistons to the oil below as it is one of the byproducts of the combustion process.
 
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manxnortonman

Well Known and Active Website User
VOC Member
Engine breathers

I run the standard timed breather on my Norvin and Rapide,but have added a D valve cap to the rear cylinder. This is vented out the via the breather tube welded to the rear mudguard on the Norvin.On the Rapide it is vented along with the timed breather throUgh alloy pipes to the rear of the machine. Neither engine leaks oil even after a porlonged blast around the M25 and very little emits from the breathers. Most of the crankcase pressure I have witnesed on british morotcycles is due to worn bores creating excess pressure which will come out somewhere.

Regards Garry
 

piggywig

Well Known and Active Website User
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

Well Known and Active Website User
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

Well Known and Active Website User
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

Well Known and Active Website User
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

Well Known and Active Website User
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

Well Known and Active Website User
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 Website 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 Website 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 Website 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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