Dieseltech or others. Sheared key on DPA pump

RGMartin · Sep 29, 2020

What would cause a timing gear key to shear on a DPA pump on a Cummins 4B? The pump feels right when rotated by hand. Sheared key was found while reassembling during overhaul(no history on machine). Machine had been recently overhauled by someone with poor attention to detail(3 cylinders were bored to .018" but had .020" pistons in them) leading to it seizing, then being left to rust.

Pump has no paint and appears to have been recently rebuilt.

Any thoughts?

Billy Shafer · Sep 29, 2020

Sounds like someone needs. A better repair shop.

David G · Sep 29, 2020

My thoughts are a seized rotor in the pump.

Al Baker(pumpman) · Sep 29, 2020

Well I will chime in as "others", 1st. Is the whole pump turning, or just the front half? Look though the holes where the high pressure lines hook and rotate it slowly,
you should see ports passing by the port with female threads. 2nd was the timing gear tight, and the key or slot hoged out? I have seen bent input shafts, It only takes
a few grand to make a problem. Did the pump use a gasket, or o ring to seal to the block? I have seen guys use to thick of a o ring and when it got tightened down it
wasnt straight to the timing cover, one side still had a small gap. This will cause a out of round situation. The key is only used for alignment, not for driving the
pump. a tight timing gear will almost always destroy a pumps insides if the key has been slipped. Al

RGMartin · Sep 30, 2020

(quoted from post at 23:05:16 09/29/20) Well I will chime in as "others", 1st. Is the whole pump turning, or just the front half? Look though the holes where the high pressure lines hook and rotate it slowly,
you should see ports passing by the port with female threads. 2nd was the timing gear tight, and the key or slot hoged out? I have seen bent input shafts, It only takes
a few grand to make a problem. Did the pump use a gasket, or o ring to seal to the block? I have seen guys use to thick of a o ring and when it got tightened down it
wasnt straight to the timing cover, one side still had a small gap. This will cause a out of round situation. The key is only used for alignment, not for driving the
pump. a tight timing gear will almost always destroy a pumps insides if the key has been slipped. Al

Thankyou for responding.

With the high pressure lines removed, there is a centered hole approximately .080" in diameter at the bottom(doesn't appear to be threaded). A punch inserted into this hole detects nothing moving at the bottom of it. With a strong light I can't see anything passing by.

The pump mounts with the triangular flat gasket. Was firmly attached. Gear was tight, and turned about 120 degrees out, with the gear's keyway raising a burr which I at first thought was a key.

Safe to assume that it is badly broken inside? I have 20+ pieces of equipment around here with DPAs, I have had lots of leaks, but never a mechanical failure like this.

Are parts available reasonably, or am I better to find a core from under my workbench to use as a donor? Thanks again

Al Baker(pumpman) · Sep 30, 2020

have repaired many seized head n rotors from Dpa pumps. Not much different than a Roosa, or Bosch rotary. Just find a donor pump with the same head ## and swap it out, and reset the fuel
calibration and timing of course .Dpa pumps are very popular so finding a good used head n rotor isnt hard or real pricey, Al

Dieseltech or others. Sheared key on DPA pump

RGMartin

Well-known Member

Billy Shafer

Well-known Member

David G

Well-known Member

Al Baker(pumpman)

Member

RGMartin

Well-known Member

Al Baker(pumpman)

Member

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