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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Oil loss through breather pipe
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<blockquote data-quote="timetraveller" data-source="post: 16625" data-attributes="member: 456"><p>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.</p><p> </p><p>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.</p></blockquote><p></p>
[QUOTE="timetraveller, post: 16625, member: 456"] 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. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Oil loss through breather pipe
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