HONDA WP30X vs WB30X vs KOSHIN SEH-80X-BAC: Complete Parts & Compatibility Guide

HONDA pump users often ask the following questions during repairs and parts searches:

1. What is the difference between HONDA WP30X and WB30X pumps?

2. Is KOSHIN SEH-80X-BAC the correct model for Honda?

3. How to find interchangeable parts?

Great perspective! You’ve touched on a topic where marketplace confusion around spare parts hits an absolute high. Let’s break it all down step-by-step: first, we’ll sort out the tricky differences between the WP30X and WB30X pumps, and then match them up with KOSHIN diagrams.

What is the main difference between Honda WP30X and Honda WB30X?

The nameplate in the photo clearly states: HONDA WATER PUMP, MODEL: WP30X, TYPE: DXE2. Many think the WB and WP series are identical, but that’s not the case. This is a classic example of OEM manufacturing:

• Honda WB30X is an original "in-house" water pump, completely designed and assembled by Honda itself at its own manufacturing plants (typically in China, Thailand, or India in recent years). It features its own unique casing mold design, original impeller part numbers, and custom mechanical seals.

• Honda WP30X is a pump manufactured under contract for Honda by the Japanese factory KOSHIN. Honda supplied its engines (GX160) and placed its signature black nameplate on the housing, but the hydraulic pumping unit is pure Koshin.

Key difference: Their internal components (pumping assemblies) are completely different. Seals, impellers, volute casings, and gaskets from an original Honda WB30X will absolutely not fit your WP30X pump. To repair a WP30X, you must search for parts using Koshin catalogs.

Does the KOSHIN SEH-80X-BAC model match your pump?

Yes, absolutely! You hit the mark. Matching the specs from your nameplate with the Koshin SEH-80X catalog confirms this:

• Connection Diameter (Connection Dia): The nameplate lists 80 mm (3 inches). In Koshin's model coding, 80 stands specifically for the port diameter (80 mm). (2-inch models carry a 50 index, like the SEH-50X).

• Delivery Volume: The nameplate indicates 1000 l/min. This is the standard rating for the Koshin SEH-80X.

• Engine (Power/Speed): The nameplate lists a power rating of 3.8 P.S. at 3600 r.p.m.—the exact net output of the legendary Honda GX160 engine.

Therefore, the provided diagram for KOSHIN SEH-80X-BAC-2 (DWG No. 011938312) is the exact factory technical manual for your WP30X pump.

Important nuances when ordering parts from this diagram

Since you have the original Koshin diagram for your pump, take note of the key high-wear components most frequently needing replacement:

• Position 8 (Impeller): Koshin part number 011053202. Ordering this from Honda WB30X is useless—they have different engine shaft thread sizes.

• Position 15 (Mechanical Seal): Koshin code 011066402 (for a 20 mm shaft). This is the most critical component. If the pump was run dry (not for nothing does the label say DON'T RUN DRY), the seal burns out first.

• Position 7 (Volute Casing): Koshin code 011317603.

• Position 23 (Large Casing O-Ring): Code 011501501 (size 1517-46.5).

Summary: Your pump is a solid Japanese Koshin machine wearing Honda outer trim. Feel free to use the attached seh-80x-bac file for selecting any parts—they will fit perfectly.

Are these other modifications compatible as well?

Be very cautious here. The short answer is: yes and no. It depends on which specific parts from these modifications (BAC-5 and BAC-6) you want to install on your pump (BAC-2).

Koshin carried out a significant internal hydraulic upgrade in these later revisions. While external components (casing, flanges) can be made to fit, the most common internal wear parts are strictly non-interchangeable.

Let's break down the details into three main categories:

What is STRICTLY INCOMPATIBLE (Internal Hydraulics)

In the BAC-5 and BAC-6 revisions, the manufacturer completely altered the geometry of the pumping assembly for better efficiency.

• Impeller — Position 7 / 8:

  • In your original scheme (BAC-2), the impeller part number is 011053202.

  • In the BAC-5 and BAC-6 diagrams, the part number changed to 012104602 / 0121046. They have different blade thicknesses and mounting depths. Putting a new impeller into an old volute casing will cause it to bind or fail to pump water.

• Volute Casing — Position 6 / 7:

  • In BAC-2, the part code is 011317603.

  • In BAC-5 and BAC-6, the part code is 012104702 / 0121047. Its geometry was altered to match the new impeller.

⚠️ Critical Repair Rule: Swapping an impeller and volute casing from BAC-5 or BAC-6 onto your BAC-2 pump can only be done as a matched pair (set). Individually, they are not interchangeable.

What fits PERFECTLY (Consumables)

Standard dimensions were maintained here, so the most common maintenance parts can safely be sourced from any of these revisions:

• Mechanical Seal — Position 14 / 15: Part number 0110664 (011066402) is identical across all versions because the Honda GX160 engine shaft diameter remained 20 mm.

• O-Rings:

  • Small Volute O-Ring (Pos. 23) 011398901 (0113989) — Identical.

  • Large Casing O-Ring (Pos. 22) 011501501 / 0123214 (size 1517-46.5 NBR) — Geometrically interchangeable.

• Check Valve — Position 3: Part number 011279901 (0112799) — Identical.

What fits, but WITH CAVEATS (Outer Casing and Flanges)

• Main Pump Casing — Position 1:

  • In your BAC-2, the part number is 012019601. In BAC-5 it is 012019602, and in BAC-6 it is 0120196. Physically, they mount onto the engine the same way, but pay attention to the upper outlet flange attachment.

• Delivery Flange and Gasket — Position 8 / 9 / 12:

  • Revisions BAC-2 and BAC-5 use flange 0110570 and classic flat gasket 011058402.

  • Revision BAC-6 replaced the flange with 0123760 and the gasket with 0123206. If you decide to swap the top flange from a BAC-6, you must buy the matching BAC-6 gasket as well.

Final Verdict: If you are looking for a mechanical seal, rubber O-rings, or check valves, you can safely buy parts from the BAC-5 and BAC-6 revisions—they will fit. However, if you need to replace the impeller or internal volute casing, source your exact original BAC-2 part numbers, or buy the BAC-5/6 impeller and volute strictly together as a set.

Which modification is the actual right one for Honda?

For the original Honda WP30X pump (shown in your photo), the baseline, original modification is specifically SEH-80X-BAC-2 (from the first document).

This comes down to how production evolved for this model:

• SEH-80X-BAC-2 is the version manufactured during the period when Honda actively commissioned this series from Koshin under its own brand (WP30X). In this version, internal parts (impeller 011053202 and volute 011317603) match 100% with what is inside your Honda-branded pump.

• SEH-80X-BAC-5 and BAC-6 are later, updated revisions by Koshin itself. By the time these came out, Koshin was primarily releasing them under its own brand (Koshin SEH-80X), though still paired with Honda engines (GX160T2 variants and beyond).

Therefore, if you are looking for replacement parts for a Honda WP30X (Type DXE2) with the black nameplate, your primary and most accurate reference guide is the DOWNLOAD PDF diagram (modification BAC-2). Ordering internal components (impeller, volute) based on it guarantees you will avoid compatibility issues.