G4-107 CP1 Pump Plunger Lapping Tool

G4-107 CP1 Pump Plunger Lapping Tool

G4-107 is a dedicated hand lapping tool kit developed for the repair of Bosch CP1 common rail high pressure pumps. It is used to restore the fit and sealing performance of the pump plunger and the control valve, which are the two most wear-sensitive precision pairs inside the CP1 pump.

What Is Included

• CP1 control valve lapping fixture — marked CP1 Control Valve Grinding, with mounting holes and a knurled adjusting knob

• Plunger lapping clamp — V-slot body with long handle and large knurled knob for clamping and rotating the plunger

• Two diamond lapping pastes — red W1.5 and blue W2.5 grades

• Small renewal parts — spring, steel balls and locating pins

Why CP1 Pumps Need Plunger Lapping

The CP1 is Bosch's first-generation common rail high pressure pump, widely used on passenger cars and light commercial vehicles. It uses a three-element plunger design with pressure control on the low pressure side. Over time the plunger and barrel pair wears, the internal clearance opens up, and the pump can no longer build full rail pressure. Typical symptoms are a long crank before start, limp-home mode, rail pressure deviation codes and metal debris in the fuel system.

Replacing the whole pump is expensive, but in many cases the plunger and barrel can be re-fitted by precision hand lapping. G4-107 gives the workshop the fixtures needed to hold both parts rigidly and to work the matching surfaces evenly with graded diamond paste.

How To Use G4-107

1. Disassemble the CP1 pump and clean the plunger, barrel and control valve thoroughly.

2. Mount the control valve into the lapping fixture and secure it with the knurled knob.

3. Apply the coarser red W1.5 diamond paste and lap the surface in a slow, even figure-eight motion.

4. Clean the part completely, then switch to the finer blue W2.5 paste for the finishing pass.

5. Clamp the plunger into the V-slot body and repeat the same lapping procedure.

6. Wash all parts, verify the fit and clearance, and re-assemble the pump.

Compatible Systems

G4-107 is intended for Bosch CP1 series common rail high pressure pumps. CP1 pumps are found on a very wide range of European diesel vehicles, including Bosch CP1 pumps fitted to passenger car and light commercial diesel engines. For pump identification, the CP1 family is recognised by its three-element plunger layout and side-mounted pressure control valve.

Frequently Asked Questions

Do I need both lapping pastes? Yes. The red W1.5 grade removes material and corrects the surface, and the blue W2.5 grade produces the fine finish required for sealing. Skipping the finishing pass leaves a surface that will leak.

Can this tool be used on other pumps? It is designed specifically for the CP1 series. Other pump families use different plunger dimensions and different control valve geometry, so they need their own fixtures.

What else should I have in the workshop? A CP1 plunger sealing test tool is strongly recommended so that the result of the lapping operation can be verified before the pump goes back on the vehicle.

Related Products

Beacon also supplies the full range of CP1 pump service tooling, including plunger sealing test tools, oil pipe repair tools and electronic pump disassembly frames. If you need a complete CP1 repair station rather than a single fixture, we can quote the whole package.

Contact

For pricing, packing details, shipping or technical questions, contact our sales team on WhatsApp: +8618253885138. We reply to technical enquiries within one working day and can supply high resolution photos, videos and drawing dimensions on request.

Introduction

G4-107 CP1 Pump Plunger Lapping Tool is a workshop hand-lapping kit for Bosch CP1 common rail high pressure pumps. It restores the plunger and control valve sealing surfaces so that a worn pump can be re-fitted instead of replaced.

System Application

Bosch CP1 common rail high pressure pump — first generation common rail pump with three-element plunger design. Suitable for passenger car and light commercial diesel engine pump overhaul.

Remote Diagnostics

Beacon offers remote technical support for pump overhaul work. Send us photos or video of the pump, the plunger and the lapping result and our engineers will advise on lapping depth, paste grade and acceptance criteria. Support is available over WhatsApp during Chinese business hours.

12 Months Warranty

All Beacon tooling carries a 12 month warranty covering manufacturing defects.

After-Sales Service

Spare lapping paste, replacement knobs and renewal small parts are available as separate items. Contact us for a full CP1 pump service package.