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Post by tangobravo on Apr 9, 2021 12:58:13 GMT -5
Got to wondering recently about crankcase sealing with the crank seals, cylinder gasket, reed valves and case integrity. This needs to hold pressure to deliver the next intake charge to the cylinder. Does anyone have any ideas on how much pressure the crankcase operates at idle and at high rpm?
Edit: This is something you can feel when pulling the start cord? One cylinder compression tug and one crankcase compression tug???
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Post by protocol1 on May 23, 2021 21:36:16 GMT -5
I think I read somewhere the crankcase pressure (average absolute pressure,) while running varies between ~ 14 psia at idle and ~ 12 psia at full load max rpm. (Sea level altitude and minimum piston ring blow-by) Of course, this is a function of the specific
properties of the engine.
The actual values for absolute crankcase pressure are effected by complex interrelated factors primarily exhaust and transfer port timing and crankcase volume.
The only way to know the actual average absolute crankcase pressure for any particular saw is to install a hose barb port for the crankcase and measure the pressure while running the saw.
The crankcase pressure cannot be felt by operating the pull starter.
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Post by tangobravo on May 25, 2021 20:03:58 GMT -5
Interesting- Gives the crank seals and the cylinder gasket a little to hold. No wonder they can fail occasionally.
Seems to be that I feel a higher compression tug on the pull rope, then a lighter 2nd one after the TDC mark. Any ideas on what that is??
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Post by protocol1 on Jun 18, 2021 0:03:20 GMT -5
Interesting- Gives the crank seals and the cylinder gasket a little to hold. No wonder they can fail occasionally. Seems to be that I feel a higher compression tug on the pull rope, then a lighter 2nd one after the TDC mark. Any ideas on what that is?? It may be possible you are feeling the crankcase compression, but it would be very light most would not feel it.
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