Why did this Bobcat hydraulic pump housing crack?

Question

I pulled a hydraulic pump off a Bobcat 863 skid steer loader today. I knew there was a crack in the outside (because it was gushing out oil), and I’m not terribly surprised that the crack goes through the block, but I struggle to explain why this happened in the first place.

Here are the best pictures I could take of the damage:

In place on the machine, before touching anything:

Still on the machine, with the end cap of the pump removed. Note the bottom left bolt hole and the crack all the way through the housing:

And with the guts removed, showing the crack running the length of the housing and detail inside the bolt hole:

I have a new pump on order, but I’m puzzling over what happened here. The machine had been leaking “a bit” for a while, then this pump failed catastrophically and spewed oil everywhere. On disassembly, the internals looked to be in great shape.

My best guess is that moisture got into the bolt hole, then froze, causing the damage? I’m having difficulty modeling the interactions in my head. Is it remotely possible that the pump was over-pressured and caused this damage to itself?

Further, anything I should do beyond replacing the pump? I’d rather not put a new one in and have it do the same thing again.

Answer 1

Most likely there was a stress riser there some place, then with the internal pressure created by the pump, a crack formed and found its way through the body. A stress riser could easily have come from a defect in the pump body or if there was a nick in just the right spot. Who really knows. I don't think there's anything you're going to do with will make things better or worse. I'd speculate with a new pump on there, you'll never see the same problem again.

Answer 2

In one of the photos, there looks like some damage -

If this wasn’t seated correctly for some reason when it was fitted, tightening the bolt may have caused the crack to start.