Oil loss through breather pipe

[John Appleton]

Hi, I am running at the moment on 20:50 Silkolene for old motors. I believe a mineral oil. Is this ok?? or should I try another oil? 20:50 chosen due to the hot weather we get in Summer in this part of the world.
Tony

Tony, I ran many miles using 20/50, and had no trouble apart from trying to buy some for topping up when abroad in Europe. When we started stocking 10/40 in bulk at our family business I started using that as it coincided with a routine engine overhaul. Many of my miles are covered in warm climates and I have no reservations about using either oil in those places.
John

 

[John Appleton]

Hi John, Can I be cheeky and ask you what type of breather valve you installed in Petes bike when you overcame the oil spillage problem through the front engine breather please. True, I have experiance of other Vintage bikes, but none at all of Vincents. So am all ears to learn and try to do things correctly.
Thank you for your input.
Tony

Tony, the breather we used is mounted on the magneto drive cover and uses the original cover as a lid. Within the housing is a spring loaded plastic valve, and the housing is vented to atmosphere through a 15mm. pipe. In the bottom of the housing is a 3mm hole which returns the oil to the crank case.
The operation is :- excessive pressure lifts the valve and vents oily air into the outer chamber as the pistons travel down the cylinders. The oil seperates out onto the walls of the chamber and finds its way down to the bottom, where it is sucked back into the timing chest as the pistons rise. The original timed breather is left in place as our one is only intended to work when crank case pressure is too high.
John

 

[tjcassar]

John,
I see so I can get this thing from the VOC??if so would you kindly give me details. Sorry to be a pest!! Re oil, Have taken on board your suggestion especially re availability abroad. I usually take some oil with me to cover the trip so this is normally not an issue. However at the rate of 1/2 a ltr daily being blown out of the breather, it does become a problem as how much oil can one pack. Obviously, the answer is to solve this issue. A bood breather valve will help. My breather pipe is a straight through bunjo bolt attached to the crank case just above my distributor. Is this supposed to be so?? or should the breather have some sort of non return ball valve as is the case on some other British bikes? Mine is straight through with nothing to close the air plus dust!! going in when the pistons are on the upward travel. I find this rather odd. So would like to know if I hasve the right part fitted.
Thank you once again.
Tony

 

[John Appleton]

Hi Tony, the breather is not available as a spare, but is of our own design and manufacture for our own use, but I am sure you will know of somebody to make you one locally. It is normal for the standard breather to be straight through as there is a sleeve valve timing device within the timing chest. This is designed to close 30 degrees after bottom dead centre of the rear cylinder, so there should be no likelyhood of dirty air being drawn in as the pistons rise, but you are quite correct in saying that a purely atmospheric breather would be a bad idea for this very reason.
From all that you have said it sounds as if you have a perfectly standard breather set up on your bike.
John

 

[tjcassar]

Hi John, I see, at least I know that what is fitted is the correct set up. Now I will monitor the situation as the running in of the engine progresses. Should it not improve, I will have no option but to fit a valve breather.
Thank you. Tony

 

[timetraveller]

Just to ensure that Tony can visualise what the original breather is like here is a description. The gear which drives the magneto/distributor is the same size as the half time pinion, i.e. it rotates at engine speed, and the gear itself has a hollow tube in the centre of it. The tube has a rectangular hole cut in it so that as it rotates this slot can act as a valve. The combination of gear and hollow shaft rotate on a hollow spindle which itself has a slot and it is the lining up of the two holes/slots which allows air to escape when the pistons are descending and, when the two slots are not lined up, stops air being sucked in when the pistons are rising. Personally I always fit the spindle so that its slot is facing downwards to try to help prevent oil escaping but that might seem a bit over cautious to some people. Phil Irving recommended widening the slot in the tube/gear pinion combination if the bike was to be used for racing. The open back end of the hollow spindle interfaces with the banjo bolt to let the air out. On ‘D’s the whole thing was got rid of and replaced by a different valve spring cap, with its own banjo bolt, but for this to be effective there has to be additional clearance in the various holes on the way to the valve spring to let the air get out to the valve cap and hence the atmosphere. Unfortunately some people do not realise this latter point and fit the ‘D’ caps without ensuring that the various holes are opened up and even worse some people leave the original breather in place which means that the engine now tries to suck air in through the top breather while the pistons are going up and then the engine has to work harder to expel this extra air when the pistons are going down. If you do not already have it then you would probably find it very advantageous to get a copy of the Spare Parts List which shows all parts of the engine and gearbox. Good luck.

 

[Tom Gaynor]

The timed "breath" exits via that banjo. Originally the pipe only went less than a foot down through the front RH engine plate and finished there. The series D breather (and Vincent improved things as they went along) had an untimed breather from a rocker inspection cap. This too had no PCV, but benefits hugely from having one fitted.

What I suggest you do is take out one section of the return pipe, the one that feeds the rockers, and see if there is a restrictor wire in the feed bolt. (The 1/4" BSF bolt that secures the banjo screws into it.) These wires reduce the flow of oil to the rockers, and were fitted as standard. Without them the oil scavenged from the crankchamber is returned quick-time to the crankchamber via the four rocker feeds, thus keeping the crankchamber full of oil which is then dumped via the breather. If there is no wire in the one you look at, there are probably none in the others. This MAY be the cause of your oil-dumping. The wires are 0.020" and a strand of clutch cable inner is about right. Heat it red hot and let it cool in air to anneal (soften) it. The wire is poked through the hole (which is about 0.030" and bloody difficult to spot), and wound round the stem of the feed bolt. This solved my problem, although my having a two-start pump was a major factor.
And if it makes no difference, it's easy to reverse.
Further advice is 1) join VOC 2) buy the books "Richardson" and "Know Thy Beast", especially the latter. Vincents are supported by very good literature, and it's well worth buying.
Here's the good news: Vincents built at the factory regularly went 50,000 miles with no trouble at all. People then did however worry less about the odd oil drip. I'm not paranoid about originality (I wouldn't be without my French button starter) but almost all of the problems I had were solved by a 50,000 mile rebore and refurb. And putting the restrictor ("jiggle") wires back in.

 

[tjcassar]

Thank you for a very detailed explanation. I did follow you especially when reading the Paul Richardson book ( A bit too short on words for me) Not being British, its rather difficult to understand first go!!
I do follow the logic though and am sure will be able to sort matters out. I have the spare parts book on back order. In the meantime, I will keep listening to what all you experienced people have to say.
Tony

 

[tjcassar]

Hallo Tom,
Your advise is very sound, as most advise has been. I like your idea of looking for the wire in the return oil feed via the rockers cover. I am not sure I understand you too well when you advise how to fit the wire should this be found missing. I understand fully the logic behind restricting the oil going throgh, although I find the wire business rather crude!! But this is just my opinion. The feed bolt , is this the one which goes through the bunjo? I will try to find out more about this beofre attempting to undo these. You say that you have a two start pump. What is this? should I upgrade mine and can help solve the problem? maybe a combination of both!! I will buy the book "Know your beast" as suggested by you. As to becoming a member, Yes of course I am becoming one, just downloaded all the papers and will send via post. Thank you for your time and priceless advise. Tony

 

[Tom Gaynor]

Sid Biberman told me the breather was better fitted to the rocker inspection covers. I admit I thought this was a refinement too far, but eventually tried it, moving the (D type + PCV) breather from the front exhaust valve cover to the front inlet rocker cover. Sid was right. It did dump less oil. It did however still dump far too much. Simon Linford advised a breather catch bottle so I could find out how much, which is good advice even if later, problem solved, one could dispense with it. But it did lead to the jiggle wire / two start pump discovery, so everything turned out well in the end.
What I like about the PCV is that it is closes the moment it has a vacuum applied. I always imagine oil forced out under crankcase pressure, about to escape to where I'll have to clean it up, being remorselessly sucked back into the engine. This is almost certainly the result of an over-active imagination, but, what the hell, simple things please simple minds.
The best of all breathers is the one on G50 Matchless's. I have one on my Manx. It consists of a flap valve (PCV) in the end of the drive-side mainshaft. It opens under pressure, closes under vacuum. It breathes to atmosphere. The genius is that centrifugal force keeps the crank axis clear of oil, so nothing comes out but oil-free air. There isn't so much as an oil-stain on the fairing immediately adjacent. Now THAT's clever.