Hitachi Zaxis 120-1 Swing Motor Leak

[cryzpene]

I have a Japan-imported ZX120-1 used to build agricultural terraces here in the Malaysian part of Borneo. It has clocked about 17000 hours so far.

Hydraulic oil mixed with gear oil started to overflow from the gear oil inlet at the bottom of the swing motor. Just prior to the leak, the swing motor started to vibrate. What we have done so far but have yet to resolve the weeks-long issue:
- replaced the seals
- replaced the shaft and bearing
- replaced the valve plate

The mechanic who has been doing the above is a very senior mechanic at a heavy machinery company who moonlights to help me. Other mechanics told me to verify that the swing motor is assembled correctly but my mechanic is adamant the assembly is correct.

Any tips/suggestion on what to look for next is greatly appreciated.

 

[mg2361]

Welcome to HEF cryzpene!

Did he check that the case drain back to tank is not clogged, kinked or restricted in any way?

 

[Tones]

Worn rotating group will cause this problem. At 17000 hours it's probably time for all new internals in that motor.

 

[cryzpene]

Worn rotating group will cause this problem. At 17000 hours it's probably time for all new internals in that motor.

Update: I brought in another mechanic. The swing motor vibrates less now but no longer leaks after 8 hours of work today. This mechanic reinstalled the disc spring inside the bushing which he said was wrongly installed by the previous mechanic. The new valve plate that was installed by the previous mechanic was taken out and the old one was put back. He said the new valve plate no longer could be used.

While it no longer leaks, he suggests replacing the rotor, piston and the other parts shown below which is quite pricey.


@Tones, is this what you more or less meant when you said replacing the internals?

 

[Tones]

Yes Sir