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My new Allis Chalmers D272 hydraulic question.
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John426 View Drop Down
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Joined: 14 Aug 2012
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Points: 312 		Post Options Post Options   Thanks (1) Thanks(1)   Quote John426 Quote  Post ReplyReply Direct Link To This Post Topic: My new Allis Chalmers D272 hydraulic question.
    Posted: 08 Jan 2025 at 4:51am

I have just completed my collection of small Allis Chalmers with a D272 model built in England.
When restarting, the hydraulic system is very weak. I only lift 300kg. After dismantling the hydraulic pump, the relief spring is broken. After changing it, I measure a pressure of 220 bars.
This pump is the same as on the C model. Same part number and spring. But I have no information on the hydraulic pressure of the D272 model. I do not have a service manual, only the parts manual.
What surprises me is that the integrated cylinder of the D272 measures 76mm in diameter, or 46 cm², which with 220 bars would gives a force of 9.6 tons and provide a lifting capacity of 1.7 tons.
This effort of 9.6 Tons seems very high for this small tractor and for the frame which is the stop for the cylinder. Isn't there a risk of breaking the lifting frame?
Any information or experiences on this subject?





Edited by John426 - 08 Jan 2025 at 4:52am
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TramwayGuy View Drop Down
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Joined: 19 Jan 2010
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Points: 11784 		Post Options Post Options   Thanks (0) Thanks(0)   Quote TramwayGuy Quote  Post ReplyReply Direct Link To This Post Posted: 08 Jan 2025 at 9:44am
Are you measuring the bore diameter or the rod diameter of the lift cylinder? I don’t think there is piston packing like on most hydraulic cylinders, so it’s the rod area that counts.
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John426 View Drop Down
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Joined: 14 Aug 2012
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Points: 312 		Post Options Post Options   Thanks (0) Thanks(0)   Quote John426 Quote  Post ReplyReply Direct Link To This Post Posted: 08 Jan 2025 at 10:06am
It is the bore diameter 3" . There is no rod , it is not a standard cylinder.










Edited by John426 - 08 Jan 2025 at 10:42am
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Gary View Drop Down
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Points: 5905 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Gary Quote  Post ReplyReply Direct Link To This Post Posted: 08 Jan 2025 at 11:51am

Hi John

For reference only, here is a Link to a picture of the Rear of a D272:

G

https://www.tamarvintagetractors.co.uk/product-page/allis-chalmers-d-272
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DiyDave View Drop Down
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Joined: 11 Sep 2009
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Points: 54450 		Post Options Post Options   Thanks (0) Thanks(0)   Quote DiyDave Quote  Post ReplyReply Direct Link To This Post Posted: 08 Jan 2025 at 2:44pm
220 bars converts to 3190 PSI, if I remember right, CA pump was 3500 PSI max, 4gpm flow rate.  Have you checked the flow rate of the pump?
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Les Kerf View Drop Down
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Points: 1395 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Les Kerf Quote  Post ReplyReply Direct Link To This Post Posted: 08 Jan 2025 at 8:10pm
Originally posted by John426 John426 wrote:

... provide a lifting capacity of 1.7 tons...

Just looking at the pictures it would appear that the relative lever ratios will reduce that lifting capacity by a significant amount. 300 kG may not be too far from reality.
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