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320C Hydraulic Pump won’t turn

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Pralhad Birdi

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Jan 30, 2018
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198
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Kenya
Hi all,
I’ve got a Japanese 320C excavator serial no. AKH 01848. The machine is working on an earth dam, excavating relatively soft material.
It’s been working without an issues, until a couple of days ago when the operator switched the machine off at lunch time. When he tried to start it up again, the engine wouldn’t turn over. We initially thought it’s a started issue, so removed that, checked it, but the starter was okay. Tried turning the engine over with a screwdriver on the flywheel, and it was a lot tighter than it should be. Pulled the sump, checked all the con and main bearings, all in order. Fearing hydraulic lock or a dropped valve above the pistons, we pulled the head. Again, all in order.
We’ve just separated the hydraulic pump from the engine now, and the engine turns freely, but the pump won’t turn.
This is a machine we’ve never had any hydraulic issues on, and we’ve been replacing the hydraulic oil and filters every 1500 hours for as long as we’ve had it (15 years).
I would really appreciate any advice on the way forward, as I’m getting the pump pulled out now and brought to the workshop. What can I check?
Thanks
 
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Pralhad Birdi

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Just a small update:
The pump has been removed, and all the oil drained. No foreign particles at all in the oil or the filters.
 
Mobiltech

Mobiltech

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You may have something jammed between the drive gears inside the pump. There are two pumps in one housing driven by helical gears. I have seen where a screw came out of one of the piston retainer plates and dropped into the gears .
 
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Pralhad Birdi

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Messages
198
Location
Kenya
Mobiltech said:
You may have something jammed between the drive gears inside the pump. There are two pumps in one housing driven by helical gears. I have seen where a screw came out of one of the piston retainer plates and dropped into the gears .
Click to expand...
So I’m guessing once I get the pump into the workshop, my best bet would be to take it apart and check for something like this? And if so, any tips on how I should go about it?
Because I’ve serviced gear pumps on our D7 3Ts, but nothing like this, so I’m slightly apprehensive about doing it.
 
Mobiltech

Mobiltech

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You can check the gears by removing the drive coupling off the input shaft and then remove the front cover/ mounting plate.
I think you will find that the pump will have to be completely disassembled cleaned and repaired . If you have rebuilt a piston pump before these are not hard to do but you will probably end up needing a reman pump if there is much damage.
 
Last edited:
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Pralhad Birdi

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Jan 30, 2018
Messages
198
Location
Kenya
Mobiltech said:
You can check the gears by removing the drive coupling off the input shaft and then remove the front cover/ mounting plate.
I think you will find that the pump will have to be completely disassembled cleaned and repaired . If you have rebuilt a piston pump before these are not hard to do but you will probably end up needing a reman pump if there is much damage.
Click to expand...
Thank you, I should be getting it in tomorrow morning, so I’ll start off with the input shaft and work my way backwards.
Any torque specs, etc. that I need to keep in mind when putting it back together? Or is there a service manual that I can follow?
 
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Pralhad Birdi

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So I’ve taken off the coupling and flange, found no debris/foreign matter in the gears. The pump is turning over with a small pipe wrench on the input shaft, but I can’t turn the shaft by hand.
I’ve taken off both of the valve bodies on either side, the ones that control the angle of the pump. Nothing amiss in there either as far as I can tell.
So my question is, is it normal for the pump to need this sort of (albeit small) force to be rotated?
 
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Pralhad Birdi

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Kenya
Thank you guys, that’s a relief to hear. Just heading out to site with the pump now, hopefully should have it fitted and be able to test by the end of the day.
 
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Gary Layton

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Glad you got it working. What actually made the hydraulic pump start working again? As I understood it, you had to the pump brought to your shop, took it apart, found nothing amiss and then took it back to the job site and re-installed. What actually fixed things?
 
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Pralhad Birdi

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Messages
198
Location
Kenya
Gary Layton said:
Glad you got it working. What actually made the hydraulic pump start working again? As I understood it, you had to the pump brought to your shop, took it apart, found nothing amiss and then took it back to the job site and re-installed. What actually fixed things?
Click to expand...
I’m genuinely not sure mate because the initial report from site was that the engine wouldn’t turn over, but once the pump was decoupled, it did. Unfortunately the head had already been removed at this point, so that cost a bit in spares and downtime.
The pump coupling had partially disintegrated, so there was a fair few sizeable aluminium bits riding around in the bell housing. I’m suspecting maybe one of them somehow got wedged between the flywheel and the bell housing, and prevented the engine from turning over.
There was a nervous moment when we put everything back together, and the engine still wouldn’t turn over, but that turned out to be the batteries. Chucked in new ones, and it started up immediately.
 
92U 3406

92U 3406

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Generally the first thing I do in a situation like that is remove or somehow disconnect whatever's hanging off the flywheel housing if it can be done in a reasonable amount time. At least then that eliminates the suspects down to the engine or the driven component(s).
 
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Pralhad Birdi

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Messages
198
Location
Kenya
92U 3406 said:
Generally the first thing I do in a situation like that is remove or somehow disconnect whatever's hanging off the flywheel housing if it can be done in a reasonable amount time. At least then that eliminates the suspects down to the engine or the driven component(s).
Click to expand...
Yeah that’s a very good policy and I think I learned that the hard way this time. Will definitely do that next time before pulling heads and sumps.
 
G

Gary Layton

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Pralhad Birdi said:
I’m genuinely not sure mate because the initial report from site was that the engine wouldn’t turn over, but once the pump was decoupled, it did. Unfortunately the head had already been removed at this point, so that cost a bit in spares and downtime.
The pump coupling had partially disintegrated, so there was a fair few sizeable aluminium bits riding around in the bell housing. I’m suspecting maybe one of them somehow got wedged between the flywheel and the bell housing, and prevented the engine from turning over.
There was a nervous moment when we put everything back together, and the engine still wouldn’t turn over, but that turned out to be the batteries. Chucked in new ones, and it started up immediately.
Click to expand...
Good feedback...thanks for the detail.
 
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