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| Bengs, Flame Eater. "Nick"......... |
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| vtsteam:
To optimize, you'd want a very free exhaust. Big port. Chimney looks like a restriction. A chimney could be big bore, or extractor cone, finned, maybe to rapid cool and act as an extractor. Fun to think about this stuff. :coffee: How does this open for exhaust? a second one way valve on top? It must be very short timing on exhaust... Floating disk valve, maybe. Maybe no spring, Does the screw set the clearance, or the spring pressure on the disk. Or is it a flapper? Floating disk would be better. Could be a ball, but more inertia -- slower acting. I'd vote for a disk. That valve inertia is critical to power output. The faster acting, the more power. |
| Stilldrillin:
--- Quote from: vtsteam on June 12, 2014, 11:03:47 AM ---Took a little head scratching to figure out what you were doing, David! :scratch: That big steel bolt was just used as a combination wrench socket and extension -- not an addition to the engine. And by turning down the diameter of the head -- you mean the head of the bolt, not the engine. Sorry, a bit dense here sometimes! :doh: Is the lack of compression due to a leak or too much head space? It does sound like tightening up the valve clearance will help. You have got me thinking about the problem of a vacuum engine valving...... :scratch: :scratch: :coffee: --- End quote --- Hi Steve. Thanks for your interest....... :thumbup: Correct. On the "big steel bolt". Which is a pifflin' 4mm dia. I turned the caphead down, to easier fit on the other nuts, which were holding bearing caps etc. Lack of "compression". (Note inverted commas). Is down to several little leaks. Aint got no valves. As such. It should make squarking noises, rotated forward. And, lock solid against vacuum, in reverse. --- Quote from: vtsteam on June 12, 2014, 11:07:52 AM ---Isn't the power stroke a vacuum, and not a result of compression on these? --- End quote --- Yes! --- Quote from: vtsteam on June 12, 2014, 11:27:46 AM ---To optimize, you'd want a very free exhaust. Big port. Chimney looks like a restriction. A chimney could be big bore, or extractor cone, finned, maybe to rapid cool and act as an extractor. Fun to think about this stuff. :coffee: How does this open for exhaust? a second one way valve on top? It must be very short timing on exhaust... Floating disk valve, maybe. Maybe no spring, Does the screw set the clearance, or the spring pressure on the disk. Or is it a flapper? Floating disk would be better. Could be a ball, but more inertia -- slower acting. I'd vote for a disk. That valve inertia is critical to power output. The faster acting, the more power. --- End quote --- Vacuum..... Therefore no gasses to exhaust. The piston created vacuum, draws in the flame. Which cools, to draw the piston back to tdc. The "chimney", houses a 6mm dia rubber ball. A one way valve. To allow any unwanted compression out, during overlap. The only valve, is the sliding shim. Sealing against the face of the cylinder head, during the vacuum stroke. David D |
| vtsteam:
--- Quote from: Stilldrillin on June 12, 2014, 04:31:57 PM --- ...The "chimney", houses a 6mm dia rubber ball. A one way valve. To allow any unwanted compression out, during overlap. David D --- End quote --- That's what I meant by exhaust and exhaust valve. The vacuum created is only partial and reduces to positive pressure as the piston moves back to the head end. That pressure is made up of the cooled gasses from the prior combustion. They contracted but didn't disappear. These must be exhausted as much as possible at TDC before drawing in the next charge of hot gas. They otherwise cool it and reduce the displacement available. This conversion from vacuum to pressure happens near TDC, so exhaust interval is extremely short. Valve action must therefore be very snappy. That means a low inertia valve, yet one with low spring pressure, since exhaust pressure is low, too. As a guess, a thin metal disk valve would have faster action than a rubber ball, so might offer the opportunity to increase performance. That's what I was mulling over. I could be wrong, but it makes me want to experiment along those lines. Too bad I'm stuck on the tractor, for the near future. And rain yesterday, today, and a real downpour predicted for tomorrow. I think your engines are just wonderful to follow, and they make me think a lot. |
| Stilldrillin:
Steve. The one, main thing, about my orphans..... There's lots of scope for thought and experiment! :thumbup: Well........ The run didn't go well. Stopping every few seconds. :scratch: I realised, the engine didn't spin over, as it had done previously. Possibly out of alignment, after I had tightened all the loose nuts? :( Time to strip further! Piston. Scuffed one one side. With what looks like ptfe tape packing......... That's not original, surely? Made from 16mm bar. Not machined on the o/d......... Looks like the oiler insert was a bit long. And held fine bits of swarf.......... Better view. Bore is badly scuffed, on the other side to the oiler........ Time for a rebore......... And hone........ Sheesh! :bang: :bang: David D |
| fcheslop:
Oh dear the joys of hot air engines :hammer: That will keep you busy marra.Never seen a piston like that one. Vac engine principles Jan Ridders has good animation http://www.ridders.nu/index.htm cheers |
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