Technical Resource
How to Rebuild a Rotary Gear Pump: Step-by-Step PA200 and PA300 Guide
A complete field rebuild of the NAPCO PA200S, PA200C, PA300S, and PA300C rotary gear pumps using a factory repair kit and standard hand tools.
When a rotary gear pump starts showing flow loss, seal weeping, or bearing noise, the decision is usually straightforward: rebuild or replace. In most field situations, a rebuild wins. NAPCO PA200 and PA300 series pumps are fully serviceable with standard hand tools, and a factory rotary gear pump repair kit contains the wear parts that actually need replacement.
This guide covers a complete rebuild of the PA200S, PA200C, PA300S, and PA300C rotary gear pumps. It applies to any NAPCO repair kit: PK200S, PK200C, PK300S, or PK300C.
When to Rebuild Instead of Replace
Rebuild when the housing, end covers, and gear bores are still in good condition. Replace the pump only when the body is cracked, the bores are deeply scored, or the cost of repeated rebuilds exceeds a new unit.
Common rebuild triggers:
- Flow loss greater than 15-20% from baseline
- Seal weeping at the shaft or end covers
- Bearing noise, rough rotation, or shaft play
- Repeated difficulty holding prime
- Visible gear wear on the tooth profiles
A NAPCO rebuild typically costs 30-50% less than a new pump and can be completed on-site in 2-5 hours. For a full cost-and-downtime breakdown, see Pump Repair Kits vs. Full Replacement. NAPCO also offers factory repair and rebuild services if you would rather not rebuild in-house.
What’s in a NAPCO Repair Kit
Every NAPCO repair kit ships in a 12″ × 18″ × 6″ carton and weighs 28 lbs for the 2″ kits and 34 lbs for the 3″ kits. The kit contents are identical across all four kits except for the two gear assemblies, which match the housing material and pump size.
| Part | Description | Qty |
|---|---|---|
| Drive gear assembly | Gear on its shaft | 1 |
| Idler gear assembly | Gear on its shaft | 1 |
| PM038 | Roller bearing | 4 |
| PM036 | High-pressure seal | 4 |
| PM037 | Low-pressure seal | 4 |
| PM007G01 | Centercase gasket, 0.008″ | 3 |
| PM007G02 | Centercase gasket, 0.016″ | 2 |
| PB43 | Cover bolt o-ring (2-012 N70) | 4 |
The PB43 o-rings seal the bearing housing cover bolts. Gasket counts are frequently transposed in the field: PM007G01 is the 0.008″ gasket and PM007G02 is the 0.016″ gasket. The stack uses five gaskets total.
The kit does not contain wear plates, assembly lubricant, the housing, or end covers. If those components are damaged, order them separately or replace the pump.
Tools and Supplies
Required:
- Torque wrench, 35 ft-lbs (48 Nm) range
- Standard socket and wrench set
- Bearing puller
- Bearing driver set or soft drift
- Feeler gauge, 0.001-0.020″ range
- Caliper (optional, for gear inspection)
- Clean rags and lint-free wipes
- Approved assembly lubricant
- Loctite 222 for set screws
- Grease gun with compatible grease
Optional but recommended:
- Brass or plastic scrapers for gasket removal
- Parts washer or mild solvent for cleaning
- Magnetic tray for bolts and small parts
Step-by-Step Rebuild Procedure
Step 1: Lock Out and Drain
Close inlet and outlet isolation valves. Open any drain plugs and allow the pump to empty. Lockout/tagout the driver per site procedure.
Step 2: Remove the Drive Coupling
Remove the coupling half or drive key. Loosen all set screws. Set aside for Loctite 222 on reassembly.
Step 3: Remove the End Covers
Remove all side cover bolts. Tap end covers straight off with a rubber mallet — avoid cocking them, which can score the housing bore. Discard old gaskets and PB43 o-rings.
Step 4: Pull the Gear Assemblies and Shafts
Slide the drive and idler gear assemblies out of the housing bore. Note orientation relative to inlet and outlet ports.
Step 5: Remove Bearings and Seals
Use a bearing puller to remove all 4 PM038 roller bearings. Press or tap out the PM036 high-pressure seals and PM037 low-pressure seals. Discard all removed bearings, seals, and o-rings. None are reusable.
Step 6: Clean and Inspect the Housing
Clean the housing bore, end covers, and all mating surfaces. Inspect for scoring, pitting, or erosion. Deep scoring across seal or gasket lands requires component replacement.
Step 7: Install New Seals
Apply light assembly lubricant to each seal OD. Press PM036 high-pressure seals squarely into bores, lip facing inward. Install PM037 low-pressure seals the same way. All 8 must be fully seated.
Step 8: Install New Bearings
Lightly lubricate each PM038 outer race. Press squarely into end cover bores using a driver contacting the outer race only. Never apply force to rolling elements or the inner race.
Step 9: Install New Gear Assemblies
Slide drive and idler gear assemblies into the housing bore. Lightly lubricate shaft journals before sliding end covers into position.
Step 10: Set Gear Clearance
Install the centercase gasket stack. Verify 0.006-0.008″ clearance with a feeler gauge, adjusting the gasket combination as needed.
Step 11: Reassemble and Torque
Install new PB43 cover bolt o-rings on all cover bolts. Start all bolts finger-tight. Torque to 35 ft-lbs (48 Nm) in a cross pattern. Verify the shaft turns freely by hand. Apply Loctite 222 to all set screws. Grease all 8 fittings until new grease appears at the bearing seals.
Step 12: Prime and Verify
Remove lockout/tagout. Open the inlet valve and prime the pump per normal procedure. Run at low speed and check for leaks, abnormal noise, or excessive heat. Gradually bring to operating speed.
Gear Clearance and Gasket Stack Detail
Correct gear clearance is the difference between a quiet, long-lasting rebuild and one that fails early. The target end clearance between the gear faces and the end covers is 0.006-0.008″.
NAPCO kits include two gasket thicknesses:
- PM007G01: 0.008″
- PM007G02: 0.016″
Typical stack combinations:
| 0.008″ (G01) | 0.016″ (G02) | Total Stack Thickness |
|---|---|---|
| 3 | 1 | 0.040″ |
| 2 | 2 | 0.048″ |
| 3 | 2 | 0.056″ |
Measure the assembled clearance at multiple points around the gear perimeter using a feeler gauge. If clearance is below 0.006″, add a gasket. If it exceeds 0.008″, remove one. Record the final stack for future rebuilds on the same pump.
Reassembly Torque and Final Checks
- Cover bolts: 35 ft-lbs (48 Nm), cross pattern
- Set screws: Loctite 222, snug plus 1/4 turn
- Shaft rotation: free by hand, no binding
- Grease fittings: pump until fresh grease appears at both bearing seals
- Leak check: 15 minutes at operating temperature before returning to service
After a successful rebuild, the pump should perform to the original flow and pressure curve. NAPCO PA300 series pumps deliver up to 158 GPM and PA200 series pumps deliver up to 69 GPM, both rated to a maximum of 100 PSI. Full performance data lives on the PA300S and PA200S product pages. To keep a rebuilt pump on curve, follow the rotary gear pump maintenance schedule. These same pumps and kits serve the fluid-transfer duties described on our general industrial applications page.
Frequently Asked Questions
When should I rebuild instead of replace?
Rebuild when flow drops, seals leak, or bearings get noisy but the housing and end covers are still sound. Replace only when the body is cracked or the bores are deeply scored.
What repair kit do I need?
PK300S for the PA300S, PK300C for the PA300C, PK200S for the PA200S, and PK200C for the PA200C.
What is the correct bolt torque?
35 ft-lbs (48 Nm), using a torque wrench in a cross pattern.
What gear clearance should I target?
0.006″ to 0.008″. Adjust by combining PM007G01 (0.008″) and PM007G02 (0.016″) gaskets.
Does the kit include O-rings and wear plates?
The kit includes cover bolt o-rings (PB43, 4 pieces). Wear plates, assembly lubricant, the housing, and end covers are not included.
Can I rebuild in the field without special tooling?
Yes. Standard hand tools only. A torque wrench, bearing puller, feeler gauge, and wrenches are all you need.
How long does a rebuild take?
Allow 2-4 hours for a PA200 series pump and 2-5 hours for a PA300 series pump, depending on accessibility and cleaning time.
Need the right kit for your pump?
Tell us your pump model and we’ll confirm the correct repair kit, contents, and lead time.