DD 2-71 fuel pressure?
Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Construction and other equipment
Forum Description: everything else with orange (or yellow) paint
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=155123
Printed Date: 20 Aug 2025 at 6:49am
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Topic: DD 2-71 fuel pressure?
Posted By: DavidnTenIll
Subject: DD 2-71 fuel pressure?
Date Posted: 28 Oct 2018 at 8:04pm
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Wondering if anyone knows what primary fuel pump pressure on a Detroit 2-71 should be at cranking speed ?
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Replies:
Posted By: Ray54
Date Posted: 29 Oct 2018 at 2:44pm
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I just remember if it was under 45psi running it was time to change filters.
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Posted By: DMiller
Date Posted: 29 Oct 2018 at 3:14pm
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Believe that was running pressure, been looking for my 71 service manual, thought cranking was like 25, have a note somewhere.
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Posted By: Coke-in-MN
Date Posted: 29 Oct 2018 at 5:02pm
Cranking or running - on startup it's low - running 15 to 25 PSI seems where mine runs . depending on RPM
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Life lesson: If you’re being chased by a lion, you’re on a horse, to the left of you is a giraffe and on the right is a unicorn, what do you do? You stop drinking and get off the carousel.
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Posted By: DavidnTenIll
Date Posted: 29 Oct 2018 at 8:14pm
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Can't see any pressure on mine when cranking (and it doesn't want to start) removed pump and ran on bench with a battery power drill that has three gear ranges. Tag on drill says 300,600,1600 rpm respectively. When I run it at 300rpm I get 10psi, at 600rpm 25-30 psi and at 1600rpm 60 psi (approximately) I don't know what rpm pump shaft turns when cranking but i see no pressure on gauge?
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Posted By: Amos
Date Posted: 29 Oct 2018 at 9:25pm
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is the pump turning? I had one that the small coupler on the driveshaft to the pump had split and fallen off...nothing worked then
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Posted By: DMiller
Date Posted: 30 Oct 2018 at 6:07am
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The other potential is the blower drive shaft splines sheared. Is a common problem on the older high hour engines. With the pump off spin the engine and see if the drive turns. If can get pressure from a drill running it then look elsewhere.
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Posted By: Eric B
Date Posted: 01 Nov 2018 at 1:47pm
I had the splines go on one of my older Detroits. Fortunately it was the splines at the pump end that were gone. I was able to buy a shaft with old (finer) spline on the end going into the blower and the new style (bigger) spline on the pump end, this way I didn't have to disassemble the blower to get fixed up.
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Currently- WD,WC,3WF's,2 D14's B. Previously- I 600,TL745,200,FL9,FR12,H3,816 LBH. Earth has no sorrow that Heaven cannot heal!
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Posted By: DavidnTenIll
Date Posted: 03 Nov 2018 at 7:11pm
Thanks for all the info. Will be checking that when I get back to it.
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Posted By: DavidnTenIll
Date Posted: 18 Nov 2018 at 6:44pm
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Did get a new pump from pro diesel. Installed, primed, and started right up. Running about 70 psi when throttled up. Dis assembled old pump. Just doesn't look that worn to me and relief valve looks ok too ? Will try to post a pic.
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Posted By: DMiller
Date Posted: 19 Nov 2018 at 5:10am
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Problem with a Positive Displacement Pump as these is they live in thousandths of an inch of tolerances. Small scratches that lead to even smooth wear grooves end up allowing the fluid in this case fuel to bypass around the gears when building pressure. Is what occurs with most hydraulic pumps, look fine but have developed a few extra thousandths of clearance and can no longer build or maintain pressure.
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