Oil loss through breather pipe

[Tom Gaynor]

Try this with your (or, better, your neighbour's) garden hose. Put four holes in it, at 20 foot intervals, starting five feet from the tap. Turn on the tap. Note how most oil, sorry, water, squirts out of the first hole, less out of the next, and so on. This is because the pressure in the pipe slowly falls off along its length. Get a long enough, small enough hose, and nothing but a dribble comes out of the end because the pressure has been dissipated in fluid friction. This also applies to long, small diameter breather pipes. Short and thick does the trick as the old saying, etc.
Now, if it was your neighbour's hose, roll it back up, and play dumb.

Best be involved in some innocent activity when next he uses it, like fitting jiggle wires to Vincents, starting nearest the tap, sorry, pump, and working downstream, because now you know that more oil goes through the first rocker feed than through the subsequent ones. Unless he reads this forum, he'll never twig. Better of course to do them all, but if you can only do one, do the first.

Later, Google SPEEDFLOW, look for check valves, then 610-06, price £15.40, and order one. I now have three, on three different bikes. They ought to be mounted horizontally, but seem to work just as well mounted vertically. And while I made couplings for one of them, screwing a breather hose on to the ends seems to work just as well.

 

[timetraveller]

I like Tom's homely analogies. We can all identity with bits of water hose and holes etc. However, I feel a certain stirring down below which might just be the curried beans but more likely is the break down of an analogy. I suspect that Tom is quite correct as far as hose pipes are concerned but now consider the following. Put your finger over the end of the hose pipe and watch the water suddenly start to spurt from all the holes. What has happened is that, despite the friction in the pipe, pressure has now built up along the whole length of said pipe. You don't believe this? Ask yourselves how piped irrigation systems work. Both the domestic ones which are used round your garden plants or the real ones where literally miles of small bore pipes carry water to the roots of crops. I know a place in the south of Spain where they grow cotton and although the main irrigation pipes have perhaps a 4" bore the pipes which go up and down the rows of cotton have an internal bore of perhaps 1/4" with an irrigation nipple every 2 feet or so. Aha I hear you cry. The difference between Tom's hose pipe and the irrigation system is only a matter of a closed end and some pressure and we all know that the Vincent oil system does not generate a significant pressure, don't we? Well that is not quite true. Consider the vertical distance from the cylinder heads to the outlet for the returning oil in the neck of the filler cap on the oil tank. It is about 10" and that means that the whole of the oil feed to the rockers is subjected to a hydrostatic pressure of about 10" of oil. Not a lot I admit but put your finger over the lower end of a 1/4" internal diameter vertical tube with about 10" of oil in it and then watch the oil flow out of it when the said finger is removed. If I am wrong then I promise that you can all hurl abuse at my bowed head while I stand in the corner in a pointy hat.

 

[Howard]

I like Tom's homely analogies. We can all identity with bits of water hose and holes etc. However, I feel a certain stirring down below which might just be the curried beans but more likely is the break down of an analogy. I suspect that Tom is quite correct as far as hose pipes are concerned but now consider the following. Put your finger over the end of the hose pipe and watch the water suddenly start to spurt from all the holes. What has happened is that, despite the friction in the pipe, pressure has now built up along the whole length of said pipe. You don't believe this? Ask yourselves how piped irrigation systems work. Both the domestic ones which are used round your garden plants or the real ones where literally miles of small bore pipes carry water to the roots of crops. I know a place in the south of Spain where they grow cotton and although the main irrigation pipes have perhaps a 4" bore the pipes which go up and down the rows of cotton have an internal bore of perhaps 1/4" with an irrigation nipple every 2 feet or so. Aha I hear you cry. The difference between Tom's hose pipe and the irrigation system is only a matter of a closed end and some pressure and we all know that the Vincent oil system does not generate a significant pressure, don't we? Well that is not quite true. Consider the vertical distance from the cylinder heads to the outlet for the returning oil in the neck of the filler cap on the oil tank. It is about 10" and that means that the whole of the oil feed to the rockers is subjected to a hydrostatic pressure of about 10" of oil. Not a lot I admit but put your finger over the lower end of a 1/4" internal diameter vertical tube with about 10" of oil in it and then watch the oil flow out of it when the said finger is removed. If I am wrong then I promise that you can all hurl abuse at my bowed head while I stand in the corner in a pointy hat.

I think you're probably right, but 10" is about 0.5 psi, plus a bit of resistance in the pipe, so Tom's idea has a lot of merit too. I'll have a look round the garden centre to see if Hoselock do a fitting for Vincent rocker feeds.

You've actually scared me with your estimate of the pressure, but looking at the return to the oil tank (even with 2 start pump) I don't think you're far off.

H

 

[Howard]

You shouldn't start me thinking, it's dangerous, I don't do it very often.

The low pressure oil system if fine for rolling element bearings, but we also have a fair number of plain bearings that may benefit from a bit of pressure.

My Comet had needle rollers in the cams and rockers, I thought it was a bit of overkill at the time, mainly because I assumed it had been done for reduced friction, but it was probably a good idea from a lubrication point of view.

Does anyone use needle rollers anymore?

H

 

[Albervin]

Is this going to be the most viewed thread in a fixed time period?? I think it says a lot about our pre-occupation with too much or too little oil! I reckon it is more beneficial than debating over the more mundane things in life such as global warming or the demise of the Euro!! What about a thread on petrol next? I filled my tank with 98 octane (zero alcohol) on Saturday morning. At lunch I had the choice of 95 Octane (E10) or 92 Octane. No Black Label. The bike told me in no uncertain terms it did not like the 95E10!!! Power was down right through the range. Would not pull 35 mph in 3rd without a protest. On the way home I topped up with 98 Octane & it was back to normal so I gave it hell!!! Series B Rapide, std. bore, 8:1, modern BT-H and standard carbs.

 

[timetraveller]

Same with me Howard. I sometimes suspect that my brain has gone down the loo. However, I am not sure about your figure of about half a pound per square inch. I did the sum the following way. Say that the 10" height is 25 cm and that the specific gravity of oil is about 0.9 gm/cc. (Water is 1.0). That means that in a 25 cm column there are 25 X 0.9 gms of weight i.e. 225 gms which will be exerting a pressure of 225 gm/square cm at the bottom of the column. In round figures there are 6.25 sq cm in a sq inch so multiply the 225 figure by 6.25 and we get 1,406 gm/sq inch which is about 3 lbs/sq inch. Not enough to be blowing your oil pipes off but significant. Over to you for either a correction or confirmation.
.
Regarding needle rollers then see recent postings by me re. modified push rods for Vincent twin clutches. I am now trying to do the same for Comets but there seems to be differences between various Comet outer clutch plates so it is taking a while.

 

[Howard]

Is this going to be the most viewed thread in a fixed time period?? I think it says a lot about our pre-occupation with too much or too little oil! I reckon it is more beneficial than debating over the more mundane things in life such as global warming or the demise of the Euro!! What about a thread on petrol next? I filled my tank with 98 octane (zero alcohol) on Saturday morning. At lunch I had the choice of 95 Octane (E10) or 92 Octane. No Black Label. The bike told me in no uncertain terms it did not like the 95E10!!! Power was down right through the range. Would not pull 35 mph in 3rd without a protest. On the way home I topped up with 98 Octane & it was back to normal so I gave it hell!!! Series B Rapide, std. bore, 8:1, modern BT-H and standard carbs.

Is that 35 mph serious, or just for emphasis?

I'm having a helluva job getting my twin to run right, and I suspect it's my lack of experience with unleaded petrol. I've nearly sussed it now (again) but last weekend it seemed to hit a wall at 80 mph. I made a few carb adjustments, and last night it was comfortably reaching 90 mph 2 up (watching for cameras) BUT I've also filled up with petrol so you've made me wonder if I've made a differemce, or just the petrol. Bring back Esso Golden!!!!!!!!!!!

H

 

[Tom Gaynor]

The analogy remains sound, although the pressure losses due to friction are reduced in your example, because flow is reduced. The pressure will still be higher in the leak nearest the tap, and lowest at the remote one.
Take the head off any convenient Rudge Ulster, every home has one, and you can prove it. The inlet rocker feed is to the centre of the pivot shaft. The only exits are two pairs of holes suitably placed to lubricate the (4" long) rocker bush - about 3 to 3 1/2" apart. As manufactured, all the holes are the same size. Squirt oil in with an oil can, and it all comes out the nearest pair, none comes out of the remote pair. To get oil to the remote pair one must reduce the near 2 x 1/8" holes to 1 x 1/16", leave the others alone. The exhaust rocker lube system is the same, but links three rockers. Same picture. To get any oil at all to the remote one, follow the same procedure, ending up with something like a 1/16" hole in the first, followed by 1/8", followed by 2 x 1/8". The only exit for oil is via the holes: the finger of Norman is not needed...
I confess I'm more used to doing these calculations for 15,000 feet of drill pipe, and accessories, but the principle is the same. What surprised me with the Rudge head was how big the disparity in delivery was in so small a compass, and that, rather than "theory" is what makes me think the first rocker feed will be better fed than subsequent ones. Whether it makes any difference to wear, I very much doubt, but then who'd have thought putting 4 x 0.020" jiggle wires into feed holes so small as to be near invisible, would improve oil consumption by ~300 mpp. Not me.

 

[Howard]

Same with me Howard. I sometimes suspect that my brain has gone down the loo. However, I am not sure about your figure of about half a pound per square inch. I did the sum the following way. Say that the 10" height is 25 cm and that the specific gravity of oil is about 0.9 gm/cc. (Water is 1.0). That means that in a 25 cm column there are 25 X 0.9 gms of weight i.e. 225 gms which will be exerting a pressure of 225 gm/square cm at the bottom of the column. In round figures there are 6.25 sq cm in a sq inch so multiply the 225 figure by 6.25 and we get 1,406 gm/sq inch which is about 3 lbs/sq inch. Not enough to be blowing your oil pipes off but significant. Over to you for either a correction or confirmation.
.
Regarding needle rollers then see recent postings by me re. modified push rods for Vincent twin clutches. I am now trying to do the same for Comets but there seems to be differences between various Comet outer clutch plates so it is taking a while.

Hi

psi = 0.434 x head in feet x SG

Amongst other things, I design the machines that go round and round on sewage works sprinkling "water" out of lots of nozzles from a single feed point. What Tom says is right, but properly designed the difference in flow at the rockers on a system like ours should be negligible - not saying it is, just that it should be. If we blocked the end of the return pipe the rockers should have the same feed rate unless the drilling is much too large and lets too much through the first hole.

I think the drillings are probably too big, but don't like the idea of blocking them with wires even though they're intended to keep the hole clear, if we had more pressure in the system I may change my view.

I use a 2 start pump because it was "fashionable" in the 70s and I only use wires if I need to combat smoke.

To throw a new spanner in. If Tom's breather is off the top of the engine (mine is from the timing case) the problem may be due to the speed of the breather air up the relatively small pushrod tunnel keeping more oil in suspension (not sure if that's the right word for oil in air).

That should keep the thread moving, if nothing else!!!

H

 

[Howard]

Same with me Howard. I sometimes suspect that my brain has gone down the loo. However, I am not sure about your figure of about half a pound per square inch. I did the sum the following way. Say that the 10" height is 25 cm and that the specific gravity of oil is about 0.9 gm/cc. (Water is 1.0). That means that in a 25 cm column there are 25 X 0.9 gms of weight i.e. 225 gms which will be exerting a pressure of 225 gm/square cm at the bottom of the column. In round figures there are 6.25 sq cm in a sq inch so multiply the 225 figure by 6.25 and we get 1,406 gm/sq inch which is about 3 lbs/sq inch. Not enough to be blowing your oil pipes off but significant. Over to you for either a correction or confirmation.
.
Regarding needle rollers then see recent postings by me re. modified push rods for Vincent twin clutches. I am now trying to do the same for Comets but there seems to be differences between various Comet outer clutch plates so it is taking a while.

Column of oil is actually - 25 x 2.54 x 2.54 cm x 0.9 = 145 grams on 1 sq inch (2.54 x 2.54)

(145 / 1000) x 2.204 = 0.32 psi 2.204 lb/kg

I would work out the amount of oil to each rocker, but it's too much like work, and to be honest I'm not sure how the viscosity of the oil and the tiny holes affect my normal calcs. I'm normally working with water through 200 off 20 mm dia holes (minimum) in 150 metres of 300 mm bore pipe - strangely, with not much more pressure - but a helluva lot more flow.

H