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Knowledge Base › Bad Excavator Pump: Rebuild with a Rotary Group or Buy a Complete Pump?
Short answer: Once the pump is confirmed worn: housing good, shaft good → rotary group (cylinder block / pistons / valve plate) + full seal kit restores like-new performance for a fraction of an assembly. Cracked housing, scored shaft or loose bearing seats → replace the assembly.
Repair / replace decision table
| What you find on teardown | Plan | Note |
|---|
| Light scoring on block/pistons, grooved valve plate | Grind or replace parts + full seals | The most common case — rotary group wins on cost |
| Seized piston, spalled cylinder block | Rotary group | Check the swash plate and servo piston while in there |
| Cracked housing, worn bearing seats | Complete assembly | The housing is the datum — not worth repairing |
| Scored drive shaft splines | New shaft or assembly | Depends on shaft availability |
Three things never to skip on a rebuild
- All seals at once — you're in there anyway; old seals will leak on reassembly;
- Cleanliness — flush the tank, change oil and filters before start-up, or the new parts die in days;
- Match the pump nameplate — brand + displacement series; send us a nameplate photo and we verify.
Get the small parts here
Tap through to our live parts search — check stock and send us the part number for an instant quote:
Frequently asked questions
How much cheaper is a rotary group?
Typically a fraction of the assembly — send the nameplate photo for an exact quote.
Which pump brands do you carry?
Kawasaki K3V/K5V, Kato, Rexroth A8VO/A11VO, Nachi and other mainstream series.
Break-in after a rotary group?
Avoid full-load shock for the first 50 hours; change oil and filters on schedule.
Got a part number or a photo?
Send it to our online chat — in-stock parts quoted the same day.