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Antique Engine Archives All archived posts from 1999 to 2004 when SmokStak was on EnginAds. This is a read-only board.

Antique Engine Archives

Will it coast LONGER or shorter?


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  #1  
Old 05-12-2004, 04:28:09 PM
Kevin O. Pulver
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Default Will it coast LONGER or shorter?

I just bought a 28" clutch pulley for my 12HP Champion/Hercules. Will the extra weight make it coast longer or shorter time periods between firings? On one hand, it seems something heavier would take longer to coast down, on the other hand, it seems something heavier would also gain less speed from each single power stroke when it hits. So it seems like it might almost make no difference at all. Is there a voice of experience out there? THanks Kevin
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  #2  
Old 05-12-2004, 05:33:52 PM
Roy Pasini
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Default Re: Will it coast LONGER or shorter?

There's a simple way to find out. Run it with and without the pulley and count RPMs. Don't waste your time theorizing.
  #3  
Old 05-12-2004, 05:49:17 PM
Mac Leod
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Default Re: Will it coast LONGER or shorter?

It should coast longer because once it gains momentum it will do a better job at keeping it, objects in motion tend to stay in motion until acted upon by an outside force (friction). Larger objects with more mass will be less effected by out side forces. It will also take longer to pick up speed because objects at rest stay at rest until acted on by an out side force (engine fireing. This is why hit n miss engines have larger fly wheels, to maintain speed. The clutch should allow for more coast time but only trying it will tell

My thoughts

Mac Leod
  #4  
Old 05-12-2004, 10:12:32 PM
Patrick McNallen
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Default Re: Will it coast LONGER or shorter?

I think that it would gain less speed from each of the power impulses, but coast longer due to having more mass in motion. It should be able to run slower, too, since more rotating weight would help to keep it from stalling on the compression stroke. I have a 20 HP 2-cycle with no clutch and lightweight steam engine flywheels. It accelerates fast, and each power impulse causes it to speed up noticably. It coasts down fast though. It won't run at a really steady speed, even though the cylinder is in good shape. I'm sure that heavier flywheels or a big heavy clutch would even it out.
  #5  
Old 05-12-2004, 10:19:50 PM
Mac Leod
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Default Re: Will it coast LONGER or shorter?

My friend, you have it right, wish I could have made it that clear...more mass moving will take longer to gain speed and it will take longer to loose speed.

Mac Leod
  #6  
Old 05-12-2004, 10:44:38 PM
Tom Cwach
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Default Re: Will it coast LONGER or shorter?

It won't change coasting time. Same rotational drag, same power input. The RPM may be more steady with the extra weight. I have a 12hp Economy with a 30" Edgemont clutch pulley. Coasts the same 36 revolutions between hits clutch in or out. If you have the pulley out and stop the pulley the engine will hit twice to get back up to speed when you engage the clutch then goes back to single hits.
  #7  
Old 05-13-2004, 04:32:52 PM
Patrick McNallen
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Default Re: Will it coast LONGER or shorter?

Tom: There is no power input when the engine is coasting.
  #8  
Old 05-13-2004, 07:55:38 PM
Tom Cwach
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Default Re: Will it coast LONGER or shorter?

There is power input when the engine comes off latchup and makes a power stroke, once in every 30 revolutions or so, your results may vary. There is rotational drag from the bearings. piston friction drag,air pumping drag from the coasting cylinder, and some air drag on the flywheels while coasting and during the power stroke. Clear enough?
  #9  
Old 05-13-2004, 08:17:40 PM
Mac Leod
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Default Re: Will it coast LONGER or shorter?

But the inertia will help over come this because of the extra mass moveing around. Notice how tops have a large heavy rim, reduce the mass of it and the top will not spin as long.

Mac Leod
  #10  
Old 05-13-2004, 08:47:52 PM
Doug Kimball
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Default Re: Will it coast LONGER or shorter?

I think Roy has best answer above.
 

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