Description
The 708-1S prefix covers several different pumps on several different machines, and that is exactly how ordering mistakes happen. On a three tonne mini excavator this item is the main pump. On a D61 or D65 dozer, a number in the same prefix group is the fan pump. Same family code, different circuit, different machine class.
Applicability
Komatsu PC27MR-2 and PC30MR-2 mini excavators, listed in parts data as the hydraulic main pump for that machine family. Komatsu’s online catalogue does not return a citable page for this number, so the item name is trade-established rather than manufacturer-confirmed, and no displacement, pressure or flow figure is published for it here.
Mini excavator pumps are not small problems
A rental fleet mini excavator runs a duty cycle that is unusually punishing for its size: hundreds of short start-stop cycles a day, hydraulic oil that spends long periods at high temperature because the machine is idling more than it is digging, and filters that get changed less often than they should because the service interval is measured in machine hours that never accumulate evenly. The pump absorbs all three.
The failure pattern is predictable: swing and boom speed fade first, the machine takes longer to fill a bucket, and oil temperature climbs because bypassed flow is doing no work. Before condemning a pump on a PC27 or PC30, check the pilot pressure and the relief settings, because a stuck relief valve on these machines produces a very similar symptom.
Diagnosis order
- Measure implement pressure and flow at working temperature.
- Check pilot pressure and relief settings before assuming pump wear.
- Inspect the oil and the return filter element; glitter in the sample changes the scope of the job.
- Confirm the suction line and strainer are clear, since starvation wears a pump that was otherwise sound.
The method is in our pump buyer’s and specification guide and regulator diagnosis and adjustment article.
Fitting and ordering
Match shaft spline, pilot, flange, port positions and control orientation against the removed pump. Prime with clean oil before cranking, change the return filter element, keep the case drain unrestricted to tank, and target ISO 4406 18/16/13. Minimum order one piece. Three to six month warranty on new aftermarket units as stated on your proforma invoice; bench checked and photographed before the wooden case closes, delivery 5 to 8 working days from payment subject to stock. The dozer fan pump in the same prefix group is 708-1S-00241, and the range sits under Komatsu hydraulic pump.
