Oil loss through breather pipe

[Tom Gaynor]

One of the Scottish Section members corrected me when I remarked that no two Vincents were alike. He said "No ONE Vincent is alike."

There are two possible reasons for making the holes too big, then adding wires. First is that the wires are an insurance against the hole being blocked by debris. I can't remember where I read that. It wasn't KTB, where it is recommended that the wires be thrown away. The second reason is that drilling a 1/32" hole is a pretty fraught business, likely to break drills. Drilling a 0.020" hole is even MORE fraught.
Richardson says that "all later machines" were fitted with wires. He doesn't say how late, but does say they should NOT be thrown away! It would seem logical that if the wires were added to later machines, there was a positive reason for this, just as, perhaps, there was a reason for the move from timed breathers to D-type breathers.
However, the over-arching rule remains "if it ain't broke, don't fix it".

 

[john998]

Hello Howard,
.32 PSI feels right, but I am confused with the following figure, ie 2.204 lb/Kg. Looks like a mixed metaphor.

Regards John.

 

[timetraveller]

Oh Dear! I see where the error occurred. In the second line of my earlier missive I multiplied 25 by 0.9 and got 225 not 22.5 Tricky little bu**ers these decimal points. It is the trouble with being an astronomer; all this is so small!! To go back to our pipes and holes in the return pipe and considering area only. I will ignore PI in the following as it goes out on both sides of any calculation. We have a main pipe with an internal diameter of 1/4", 250 thou, radius 125 thou. Square that and we get 15,625 square thous (ignoring PI). Suppose the holes in the rocker feed bolts are 30 thou diameter, 15 thou radius, square that and we have 225 square thous. There are four holes giving a total of 900 square thous for the oil to trickle through compared with the 'gallery' pipe of 15,625. About 6%. So how is it that a six percent bleed off of oil from a pipe can give so much oil loss as Tom experienced on his bike. In the old days when we had valve guides without seals then I can imagine at least the inlets sucking oil from the rockers down the lower valve guides on the induction stroke. Assuming that were are seals in the guides and that all was in good order then where is Tom's extra oil going? I know there are people out there who have fitted low clearance pistons and sealed valve guides who get about 2,000 miles to the pint. What I do not know is whether they are using restrictor wires or not or twin start oil pumps or not.

On the subject of pressure loss down a tube; anyone who has tuned an engine in the last 40 years or so will know that if one wants to maintain atmospheric pressure behind the inlet valve head then one has to have an inlet tract with an included angle of about 7 degrees. This is due to frictional losses down the inlet tract. Sadly when doing the calculations for a Vincent this leads to unfeasibly large carburettors etc. Down draft fuel injected engines seem to get away with it and the contemporary use of either supercharges or turbocharges means that normal aspiration is uncommon now on performance engines. Over to you chaps.

 

[Howard]

Hello Howard,
.32 PSI feels right, but I am confused with the following figure, ie 2.204 lb/Kg. Looks like a mixed metaphor.

Regards John.

Sorry John,

It didn't post the way I typed it. For some reason I divided by 1000 to change grams to kg then multiplied by 2.204 to convert kg to lbs............... 2.204 lbs/kg was my "working out in the margin" if you see what I mean.

 

[Howard]

Oh Dear! I see where the error occurred. In the second line of my earlier missive I multiplied 25 by 0.9 and got 225 not 22.5 Tricky little bu**ers these decimal points. It is the trouble with being an astronomer; all this is so small!! To go back to our pipes and holes in the return pipe and considering area only. I will ignore PI in the following as it goes out on both sides of any calculation. We have a main pipe with an internal diameter of 1/4", 250 thou, radius 125 thou. Square that and we get 15,625 square thous (ignoring PI). Suppose the holes in the rocker feed bolts are 30 thou diameter, 15 thou radius, square that and we have 225 square thous. There are four holes giving a total of 900 square thous for the oil to trickle through compared with the 'gallery' pipe of 15,625. About 6%. So how is it that a six percent bleed off of oil from a pipe can give so much oil loss as Tom experienced on his bike. In the old days when we had valve guides without seals then I can imagine at least the inlets sucking oil from the rockers down the lower valve guides on the induction stroke. Assuming that were are seals in the guides and that all was in good order then where is Tom's extra oil going? I know there are people out there who have fitted low clearance pistons and sealed valve guides who get about 2,000 miles to the pint. What I do not know is whether they are using restrictor wires or not or twin start oil pumps or not.

On the subject of pressure loss down a tube; anyone who has tuned an engine in the last 40 years or so will know that if one wants to maintain atmospheric pressure behind the inlet valve head then one has to have an inlet tract with an included angle of about 7 degrees. This is due to frictional losses down the inlet tract. Sadly when doing the calculations for a Vincent this leads to unfeasibly large carburettors etc. Down draft fuel injected engines seem to get away with it and the contemporary use of either supercharges or turbocharges means that normal aspiration is uncommon now on performance engines. Over to you chaps.

Phewwwwwwwww - I don't think I've ever seen anyone work out area in square thous before - you astronomers like your accuracy, don't you?

I've always been baffled where oil goes - but I know lots of it has landed on my boots and trousers over the years.

So, 7 degree taper from oil tank down to pump on the 1/4" oil pipe - and you thought getting the carbs and inlet tracts right was difficult.




Tom

I think you're on the right track I seem to remember that the joggle wires are so called because they joggle around to keep the oil hole clear, the holes are too big on purpose, and the wires should be a loose fit to allow them to move, but that could have been Vincent myth or PR, and as you say it's just easier to drill the bigger holes.

As an aside. When I started racing my Comet, I had to drill lots of nuts with a 1/16" hole to wire them. I broke so many drills, in despair I went into the local hardware shop and asked the young girl behind the counter for twelve sixteenths drill bits - she brought me one
3/4" drill bit - couldn't fault her maths!!! Long time ago, when kids understood real units>

H

 

[Tom Gaynor]

But there ARE 2.2 lb per kilo.... A kilo is 2.2 lb.

 

[timetraveller]

The seven degree included angle does not apply to oil pipes. The figure depends upon the viscosity of the fluid, air in one case and oil in the other. So relax, you do not have to modify the oil pipes.

 

[Howard]

But there ARE 2.2 lb per kilo.... A kilo is 2.2 lb.

Tom

I was a bit confused about that too.

John

Please explain "mixed metaphors" for us thickies - no offence meant Tom.

H

 

[john998]

Dear Howard,
Cribbed from Google 'Something used to represent another; a symbol.'
In the usual perversity of Vincent's, my solo has all the new bits, and needs a version of the elephant trunk
breather to keep the oil consumption down. The outfit gets the cast off's and even though working harder
than the solo manages fine on a standard timed breather.
Off to Applecross tomorrow on the outfit, camping made easy.
Regards John

 

[ernie]

Hi Tony, kif inti?

You started such a fascinating thread. It has excited me so much I am moved, uncharacteristically, to add my £200 worth.

First off, the standard breather on a Vincent twin is generally accepted as adequate for a normal road-going machine in good fettle. However it is also known that at tickover it will drip oil. So your breather is working normally in my opinion. The breather can be overwhelmed if there is too much blow-by past the piston rings because, as I believe to be in your case, they have not yet bedded in. 500 miles would be adequate if you ran in properly, giving it a few good squirts, up to half throttle, to force the rings against the bores. If one poodles around, it will take longer. But even when bedded in, the breather will still drip at tickover. This is simply because the timed breather valve inside the timing cover is located in a particularly oily place.

There are many many solutions to this problem. You can use a catch bottle. You can fit another breather and there are many many ways of doing this. Everyone has their favourite method and swears by it to the exclusion of all others. Tom Gaynor has his. The Appleton layer have theirs and there are many more. I have mine but I will not burden the list with a description now, unless there is a chorus of encouragement... hello... hello... curious silence.

Forget the metering wires issue. It is only significant if you suffer from a chronically smokey exhaust or oiling plugs.

Forget the 2 start pump worm issue. The standard one is perfectly adequate and you really do not want to go there.

I hope that helps. I look forward to meeting you somewhere on our bikes.

Best regards and warm encouragement from

Ernie Lowinger
born in Malta G.C. 11 My 1942