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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Cam Wear
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<blockquote data-quote="timetraveller" data-source="post: 93635" data-attributes="member: 456"><p>Hi Vic, I'm not sure that I understand the test. When you say "disconnect the return line" do you really mean disconnect or block off. The way that I understand it is that however much the 'feed' side of the pump is circulating the 'return' side tries to take more. I don't think that one could do anything with the pipes to fill up the sump. It might work if one filled the sump up first before starting the engine so that for a while the return side only sucked oil and no air. When I've been involved with engines like that the amount of smoke produced means that one does not want to do it for too long. I've run two start pumps in all my engines for years and the speed at which the oil starts to return to the tank compared with a single start pump makes me very happy that I do. There are people who have trouble with oil or oil vapour escaping from the oil filler in the middle of the petrol tank and so do not like the twin start system. However, it is the simplest thing to stop that. I used a curved piece of 'baked bean can' (cans for other purposes are available). I fastened one end under the adjusting screw for the chain feed and then gently curved the piece of metal backwards and downwards. This ensures that the returning oil follows a nice smooth path downwards and completely stops any upwards spray.</p><p>If I'm right about the pressure building up due to restrictions in the return line when a two start pump is used then any air bubbles would also be slightly compressed and help to smooth out the feed to the various orifices. The air (gas) can be compressed while the oil cannot. (For pedants I know that is not exactly true but it is near enough for this problem.)</p></blockquote><p></p>
[QUOTE="timetraveller, post: 93635, member: 456"] Hi Vic, I'm not sure that I understand the test. When you say "disconnect the return line" do you really mean disconnect or block off. The way that I understand it is that however much the 'feed' side of the pump is circulating the 'return' side tries to take more. I don't think that one could do anything with the pipes to fill up the sump. It might work if one filled the sump up first before starting the engine so that for a while the return side only sucked oil and no air. When I've been involved with engines like that the amount of smoke produced means that one does not want to do it for too long. I've run two start pumps in all my engines for years and the speed at which the oil starts to return to the tank compared with a single start pump makes me very happy that I do. There are people who have trouble with oil or oil vapour escaping from the oil filler in the middle of the petrol tank and so do not like the twin start system. However, it is the simplest thing to stop that. I used a curved piece of 'baked bean can' (cans for other purposes are available). I fastened one end under the adjusting screw for the chain feed and then gently curved the piece of metal backwards and downwards. This ensures that the returning oil follows a nice smooth path downwards and completely stops any upwards spray. If I'm right about the pressure building up due to restrictions in the return line when a two start pump is used then any air bubbles would also be slightly compressed and help to smooth out the feed to the various orifices. The air (gas) can be compressed while the oil cannot. (For pedants I know that is not exactly true but it is near enough for this problem.) [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Cam Wear
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