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Harry Ferguson Tractors Discussion Forum
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dwell/tack

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dfitch

01-15-2006 09:09:53




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I want to use a dwell/tack on my Ferguson and the dwell/tack I have only has an 8 clyinder scale.

Am I right in assuming that to correctly translate the readings from the 8 clyinder meter to the 4 clyinder motor that I need to double the dwell reading and divide the RPM reading by 2




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Fred Martin

01-18-2006 10:35:21




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 Re: dwell/tack in reply to dfitch, 01-15-2006 09:09:53  
Heres what it says on the face of the dwell meter in front of me...4cyl = 8cyl X 2. So I"m assuming that you would do it for the tach, dwell and points scales. I now come to a question....if the tractor is positive ground, won"t you have to hook the meter up backwards to keep polarity correct for the meter?... as you can see...I haven"t used mine on the Fergeson 20 but probably could on the MF-35, as it"s 12 volts and negative ground. I think I"ll try it on the 20...as soon as I cut the old expired tire off the back and charge the battery and....well, I bought this old 48 Plymouth and a Mopar engine and 727 transmission....and, you know...things have their priority. Fred OH

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Dennis P in Ohio

01-16-2006 05:53:49




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 Re: dwell/tack in reply to dfitch, 01-15-2006 09:09:53  
Good question. I can't answer, but maybe you could help me with the hook-up. I haven't used mine in so long, I cannot remember how to hook it up, and I lost the book that came with it.
Thanks.



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dfitch

01-16-2006 06:12:11




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 Re: dwell/tack in reply to Dennis P in Ohio, 01-16-2006 05:53:49  
My dwell/tack has 2 wires on it. I hook the red lead from the meter to the side of the coil that goes to the distributor and the black meter lead to tractor ground. This is on a 12 volt to-30

I get good reading just don't know how to correctly translate. I guess I'm mathmaticaly challenged.



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Jim in OH

01-16-2006 11:00:59




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 Re: dwell/tack in reply to dfitch, 01-16-2006 06:12:11  
If it is set to 8-cyl mode but connected to a 4-cyl engine (at the coil) then:

1- The RPM reading that you see on the meter will be 1/2 of the actual RPM of the engine. The meter "counts" the opening and closing of the points and your 4-cyl will only have half as many counts as the 8 cyl at the same RPM. Multiply reading by two to get the correct RPM.

2-Dwell reading that you see on the meter is the fraction of the time that the points are CLOSED. At "0%" they are closed none of the time (always open) and at "100%", they are closed all of the time (never open). Dwell should usually be in the range of nominally 60% closed. Unfortunately someone decided to calibrate dwell in degrees turned by the distributer, instead of percent clsoed so they now have to make multiple scales on the meter.... so on an 8-cyl engine, 360/8=45 degrees is 100% and on a 4-cyl 360/4=90 degrees is 100%. With the meter set for an 8cyl, 60% on the meter will read 27 degrees but the actual dwell angle of your 4-cyl distributor will be 54 degrees (60% of 90). Multiply dwell meter reading by two to get actual 4-cyl measurement. (Note that the correct needle position is still in the range 60% of full scale. If you are setting new points, I would use the manufacturer gap then read the dwell for calibration use with used points later...)

Jim

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gerard

01-15-2006 09:43:09




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 Re: dwell/tack in reply to dfitch, 01-15-2006 09:09:53  
Thought you"d have to multiply rpm by 2



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