small frame gas pump

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This section describes the small frame pump assemblies powered by gasoline engines intended for use in light dutyapplications. This small frame gas pump may also be referred to as ‘GPW-EG’ or ‘EG’ or ‘Economy Gas’ pumps. Most of theinformation previously printed in publication A4453 will be found here.

The small frame gas pump has the following features:

• 1500 to 1800 PSI water pressure

• 2.0 Gallons per minute flow

• Axial Cam Design

• Stainless Steel Pistons

• Fixed Pressure Unloader

• Chemical Injection System available

• Thermal Relief Valve available

• Oil Bath Drive System

• Vertical or Horizontal Engine Mount

Part 1 - Specifications and ViewsThis section presents the torque and performance specifications for Generac Portable Products® small framegas pumps. Also presented are sectional and exploded views of this type of pump assembly.

Performance Specifications

+ Pressure (in pounds per square inch) is adjustable up to the unit's rated pressure.

* Flow rate is given in gallons per minute.

‡ ‘A’ suffix denotes pumps with thermal relief valve.

Pump assemblies are listed by part number and were current at time of publication. Other pump assemblies will becomeavailable as our products evolve.

SMALL FRAME GAS PUMP

Section 5 • Small Frame Gas Pump

Portable Pressure Washer Familiarization and Troubleshooting Guide

Pump Rated Engine Pump Head Flow Rate* Piston Oil Type/Assembly Pressure+ Shaft Material CapacityPart No.‡

B1906A 1500 Straight Aluminum 2.0 Stainless Steel 80W90/120ml20965 1650 Straight Aluminum 2.0 Stainless Steel 80W90/120ml

20965A 1650 Straight Aluminum 2.0 Stainless Steel 80W90/120mlB1262 1750 Straight Aluminum 2.0 Stainless Steel 80W90/120ml

B1262A 1750 Straight Aluminum 2.0 Stainless Steel 80W90/120ml

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Cross-Sectional view A typical small frame gas pump is shown in cross-section inFigure 5.1.



Figure 5.1 — Small Frame Gas Pump (cross-sectional view)

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1 3 Rubber grommet spacer sleeve

2 1 Cage needle bearing assembly

3 1 Bearing washer

4 1 Bearing washer

5 3 Oil piston seal

6 3 Piston return spring

7 3 U-cup seal

8 1 Axial cam w/insert

9 1 Engine adapter

10 1 Piston and unloader housing

11 3 Piston spring retainer

12 3 Pilot spacer

13 3 Piston

14 1 Pump head

15 1 Radial ball bearing

16 6 Rubber bushing


O-Ring seal

18 1 High pressure transfer O-Ring

20 6 Check valve assembly

21 3 Outlet check valve cap O-Ring

22 1 Thermal relief valve (if equipped)

w/sealant

23 3 Outlet check valve cap

24 1 Unloader seat

25 1 Unloader seat O-Ring

26 1 Unloader piston

27 2 Unloader split-ring seal

28 1 Unloader spring

29 1 Unloader cap O-Ring

30 1 Unloader cap

31 1 Pipe plug (if item 22 notequipped) w/sealant

32 1 Chemical injection hose barb

33 1 Plug, w/sealant

34 1 Chemical injection ball

35 1 Chemical injection spring

36 1 Chemical injection venturi

37 6 Low pressure transfer O-Ring

39 7 Lock washer

40 4 Socket head cap screw

M6-1.0 x 35


M6-1.0 x 25

43 1 Venturi O-Ring



Item Qty. Description Item Qty. Description

Cross Sectional View Parts List

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Exploded View A typical small frame gas pump is shown in exploded view inFIgure 5.2.



Torque Chart

Item Torque

23 15-17 ft-lbs

30 Brass: 15-18 ft-lbs

Plastic: 7-10 ft-lbs

31 15-18 ft-lbs

32 9-12 in-lbs

33 12-15 ft-lbs

36 20-30 in-lbs

40 9-12 ft-lbs

42 9-12 ft-lbs

43 15-18 ft-lbs

Figure 5.2 — Small Frame Gas Pump (exploded view)

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1 3 Rubber grommet spacer sleeve

2 1 Cage needle bearing assembly

3 1 Bearing washer

4 1 Bearing washer

5 3 Oil piston seal

6 3 Piston return spring

7 3 U-cup seal

8 1 Axial cam w/insert

9 1 Engine adapter


11 3 Piston spring retainer

12 3 Pilot spacer

13 3 Piston

14 1 Pump head

15 1 Radial ball bearing

16 6 Rubber bushing


O-Ring seal

18 1 High pressure transfer O-Ring

20 6 Check valve assembly

21 3 Outlet check valve cap O-Ring

23 3 Outlet check valve cap

24 1 Unloader seat

25 1 Unloader seat O-Ring

26 1 Unloader piston

27 2 Unloader split-ring seal

28 1 Unloader spring

29 1 Unloader cap O-Ring

30 1 Unloader cap

31 1 Pipe plug (if item 43 notequipped) w/sealant

32 1 Chemical injection hose barb

33 1 Plug, w/sealant

34 1 Chemical injection ball

35 1 Chemical injection spring

36 1 Chemical injection venturi

37 6 Low pressure transfer O-Ring

39 7 Lock washer


M6-1.0 x 35


M6-1.0 x 25

43 1 Thermal relief valve (if equipped)

w/sealant

45 1 Venturi O-Ring



Item Qty. Description Item Qty. Description

Exploded View Parts List

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Part 2 - DisassemblyGeneral Information & Special Tools

NOTE: There are no special tools required todisassemble or reassemble this pump.

CAUTION: The pump is full of oil. Whenremoving pump from engine, drain by pouring oil outof port used by the crankshaft.

Pump Head

Refer to Figure 5.3 for this procedure.

Using a 5mm Allen wrench, remove the four (4) M6-1.0 x35 cap screws and lockwashers to separate pump head frompiston housing.

To disassemble pump head:

1. Remove the three (3) water seals. Seals should slide outby hand.

2. Remove the three (3) inlet check valves. A 5/16”-18bottoming tap may be used to remove these valves. DONOT use a screwdriver as it will damage valve and head!

3. Remove the O-Ring from the high pressure transfer boss.

4. Remove the three (3) M8-1.5 outlet check valve caps andO-Rings.

5. Remove the three (3) outlet check valves and O-Rings.

6. Do not attempt to remove the pipe plug (item 7). It isinstalled with a thread-locking compound and is notmeant to be removed.

Piston & Unloader Housing Removal

Refer to Figure 5.4 for this procedure.

Before disassembling the piston and unloader assembly, dothe following:

1. Remove the three (3) pilot spacers. These will just slideoff.



Figure 5.3 - Pump Head

Item Name

1 Water seal

2 Check valve

3 Low pressure transfer O-Ring

4 High pressure transfer O-Ring

5 Outlet check valve cap

6 Outlet check valve cap O-Ring

7 Pipe Plug - If present, DO NOT REMOVE

8 M6 lock washer

9 M6-1.0 x 35 cap screw

Figure 5.4 - Pump-Adapter Assembly

Item Name

1 Piston

2 Pilot spacer


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2. Remove the three (3) low pressure transfer O-Rings.

WARNING: There may be up to 75 pounds ofstored energy when separating the piston andunloader housing from the engine adapter housing.Remove these bolts slowly and evenly.

3. Apply a 6” C-clamp to hold the engine adapter and thepump head together.

4. Remove the three (3) M6-1.0 x 25 cap screws that holdthe engine adapter to the piston and unloader housing, asseen in Figure 5.5.

5. Slowly loosen the C-clamp until spring tension is releasedand the components separate.

Piston & Unloader Housing Disassembly

Refer to Figure 5.6 for this disassembly, as follows:

1. Remove O-Ring from housing.

2. Remove the three (3) pistons, springs, and retainers. Todo this, grasp the piston springs and pull straight out. Theretainers will stay attached to the pistons.

3. Remove the three (3) piston oil seals.

4. Remove the thermal relief valve (if present). It is notnecessary to remove the pipe plug, if installed in place ofthe thermal relief valve.



Figure 5.6 - Piston & Unloader Housing

Item Name

1 O-Ring

2 Piston and retainer

3 Spring

4 Thermal bypass valve or pipe plug

5 Piston and unloader housing

6 Piston oil seal

Figure 5.5 - Engine Adapter

Item Name

1 M6-1.0 x 25 cap screw & M6 lock washer

2 Engine adapter

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Chemical Injection System

Refer to Figure 5.7 and follow this chemical injection systemdisassembly procedure.

CAUTION: Be careful not to lose check ball andspring.

1. Remove the chemical injection fitting, check ball, andspring.

2. Using a large straight tip screwdriver, unscrew andremove the chemical injection venturi and O-Ring fromdischarge port.

Unloader

Refer to Figure 5.8 when following this disassemblyprocedure.

CAUTION: Unloader cap is under strong springpressure.

1. Remove the M25-1.0 unloader cap with a 24mm wrench.

NOTE: Unloader cap, unloader spring, andunloader piston parts may show some slightdifferences depending on production date. If theentire unloader system is replaced, newer assembliesare completely interchangeable with older models.

2. Remove the unloader spring and the unloader piston.These pieces should just slide out.

3. Remove the unloader seat by inserting a 90° O-Ring pickinto the orifice machined in the side of the seat, thengently pull the seat out of the housing.



Item Name


2 O-Ring

3 Unloader seat

4 Unloader piston

5 Unloader cap

6 Unloader spring

7 Split-ring seal

Figure 5.7 - Chemical Injection System

Item Name

1 Chemical injection venturi

2 O-Ring

3 Barbed nipple

4 Check ball

5 Spring


Figure 5.8 - Unloader Parts

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Engine Adapter

Refer to Figure 5.9 when following this disassemblyprocedure.

1. Remove the thrust washer.

2. Remove the cage needle bearing.

3. Remove the retainer washer.

4. Remove the axial cam/radial ball bearing assembly.Because the bearing is pressed onto the cam, the cam andbearing must be replaced as an assembly.

5. If present, the pipe plug was installed with a thread-locking compound and should not be removed.

Part 3 - InspectionSeals, O-Rings, and Gaskets

Once the pump is disassembled, make a careful inspection ofall seals and O-Rings for any defects that may affect theproper operation of the pressure washer.

Piston & Spring Assemblies

Referring to Figure 5.10, inspect the three (3) pistonscarefully. Reject any piston that is scratched, dented, orotherwise damaged.

CAUTION: Do not strike a piston with any objector use a piston to strike any object.Do not drop thepiston. Dropping the piston will result in damage.



Figure 5.9 - Engine Adapter & Axial Cam

Item Name

1 Thrust washer

2 Cage needle bearing

3 Retainer washer

4 Axial cam

5 Radial ball bearing

6 Engine adapter

Figure 5.10 - Piston Assembly

Item Name

1 Retainer

2 Piston

3 Spring

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Each of the three (3) pump pistons pass through an oil sealin the piston and unloader housing. Note the oil seal andpilot spacer illustrated in Figure 5.11. The oil seal lip will facetowards the piston spring and retainer to retain the pumpoil.

Inspect the three (3) piston springs. Replace any spring thatis damaged or broken.

Engine Adapter, Pump Head, and Piston & UnloaderHousing

Clean all parts. Inspect carefully for cracks, damage, and soforth. Check for corrosion. Replace any damaged, defective,or corroded part as necessary.

Axial Cam Drive Components

Referring to Figure 5.12, carefully inspect the engine adapterbearing and the axial cam bearing assemblies for wear,damage, and freedom of rotation. Replace any damaged ordefective bearing assembly.

Inspect the retainer washer and the thrust washer. Replaceif damaged.

Inspect the axial cam. Replace if worn excessively ordamaged.



Figure 5.11 — Piston Chamber

Item Name


2 Piston

3 Oil seal

4 Pilot spacer

5 Pump head

Figure 5.12 - Axial Cam Drive Components

Item Name

1 Thrust washer

2 Cage needle bearing

3 Retainer washer

4 Axial cam

5 Radial ball bearing

6 Engine adapter

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Part 4 - Reassembly

NOTE: Refer to the Torque Specifications providedon the pump exploded view found at the beginning ofthis section when reassembling this product.

Engine Adapter

1. Install the retainer washer (thinner one) on the axialcam/radial ball bearing assembly.

2. Install the cage needle bearing (either side up).

3. Install the thrust washer (thicker one, either side up).

Unloader Assembly

Refer to Figure 5.13 for this assembly.

1. Install the new O-Ring on the unloader seat (if replacing).

2. Install the unloader seat with O-Ring (use a small amountof petroleum jelly on O-Ring if necessary). Seat will pressitself into place when unloader piston, spring, and cap areinstalled.

3. Install the new split-ring seal onto the unloader piston (ifreplacing).

4. Install the unloader piston. It will seat itself inside of theunloader seat.

5. Install the unloader spring.

6. Install the M25-1.0 unloader cap and O-Ring.

7. Tighten the unloader cap to the torque value specified inthe Torque Chart, found on Figure 5.2 (Exploded View) atthe beginning of this chapter.

Chemical Injection Assembly


1. Install the check ball into the chemical injection nipple,followed by the spring (with the small end of the springtowards the ball).

2. Install the M10-1.0 chemical injection nipple into thepiston and unloader housing. Be careful to not drop theball and spring.

3. Tighten the chemical injection nipple to the torque valuespecified in the Torque Chart, found on Figure 5.2(Exploded View).



Figure 5.14 - Chemical Injection System

Item Name

1 Chemical injection venturi

2 O-Ring

3 Barbed nipple

4 Check ball

5 Spring


Figure 5.13 - Unloader Assembly

Item Name


2 O-Ring

3 Unloader seat

4 Unloader piston

5 Unloader cap

6 Unloader spring

7 Split-ring seals

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4. Install the chemical injection venturi O-Ring into thepiston and unloader housing.

5. Hand thread the M14-1.25 chemical injection venturi intothe housing.

6. Tighten the venturi to the torque value specified in theTorque Chart, found on Figure 5.2 (Exploded View).

Piston & Unloader Housing Assembly


1. Refer to Figure 5.15 and install the three (3) oil seals.Press the seals into the piston and unloader housing usinga small amount of petroleum jelly.

NOTE: Do not reuse springs color coded RED. Allpiston return springs must be replaced in sets ofthree (3).

2. Apply a small amount of 80W90 oil to the three (3)pistons, then install the pistons, springs, and retainers intothe piston and unloader housing. The pistons are merelypushed into place.

3. Install the thermal relief valve (item 3).

4. Tighten the thermal relief valve (or substitute plug) to thetorque value specified in the Torque Chart, found on Figure5.2 (Exploded View) at the beginning of this chapter.

Pump Head Assembly


1. Install the three (3) low pressure transfer O-Rings. Use asmall amount of petroleum jelly to hold them in place.

2. Install the high pressure transfer O-Ring. Petroleum jellywill help to hold it in place.



Figure 5.15 - Piston & Unloader Housing

Item Name

1 O-Ring

2 Piston and retainer

3 Spring

4 Thermal bypass valve or pipe plug


6 Piston oil seal

Figure 5.16 - Pump Head

Item Name

1 Water seal

2 Check valve


4 High pressure transfer O-Ring

5 Outlet check valve cap

6 Outlet check valve cap O-Ring

7 Pipe Plug - If present, DO NOT REMOVE

8 M6 lock washer


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3. Press three (3) inlet check valves into place, as shown inFigure 5.16.

4. Install three (3) outlet check valves, observing theirorientation, as shown in Figure 5.16.

5. Install the three (3) M18-1.5 outlet caps and O-Rings.

6. After the head is bolted to the pump, tighten the three(3) outlet caps to the torque value specified in the TorqueChart, found on Figure 5.2 (Exploded View) at thebeginning of this chapter.

Main Component Assembly


1. Place the pump head assembly on a flat surface, with theinner side up.

2. Position the piston and unloader housing on the pumphead so that the pistons line up with their respectivecylinders in the pump head.

3. Place the piston housing O-Ring into the groove on thehousing.

4. Grasp the engine adapter with both hands and invert itwhile holding the axial cam, washers, and bearing in place.

5. Place the engine adapter over the piston housing so thatthe thrust bearing is touching all three (3) pistons, and themounting screw holes on the adapter line up with thethreaded holes on the housing.

6. Referring to Figure 5.18, install the three (3) M6-1.0 x 25socket head cap screws into the mounting screw holes onthe engine adapter and thread them into the pistonhousing.

7. Tighten the M6-1.0 cap screws to the torque valuespecified in the Torque Chart, found on Figure 5.2(Exploded View) at the beginning of this chapter.

NOTE: The engine adapter bolt holes line up withthe holes on the piston housing in one position only.Use the widest of the three openings between theengine adapter ‘legs’ as a reference. This openingshould line up roughly with the chemicalinjection/thermal relief valve side of the pistonhousing.



Figure 5.18 — Installing Engine Adapter Bolts

Item Name

1 M6-1.0 x 25 cap screws & M6 lock washers

2 Engine adapter

3 Widest opening between three (3) engine adapter‘legs’ aligns with the chemical injector-thermal relief side of piston and unloader housing

4 Pump head

Figure 5.17 — Main Component Assembly

Item Name

1 Engine adapter assembly with axial cam, bearings,and washers held in place.

2 Assembled piston and unloader housing withpistons, seals, and O-Ring

3 Pump head assembly placed on flat surface

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Pilot Spacer Installation

1. Grasp the complete pump assembly with both hands andturn it over onto the three (3) engine adapter ‘legs’, asshown in Figure 5.19.

2. Carefully lift the pump head from the pump and slide thethree (3) pilot spacers over the pistons, which will beprotruding from the piston housing.

3. Install the three (3) low pressure transfer O-Rings aroundthe inlet openings on the piston housing, as seen in Figure5.20.



Figure 5.19 — Invert Pump Assembly

Figure 5.20 — Install Pilot Spacers/O-Rings

Item Name

1 Pump head

2 Pilot spacer


4 Piston

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Pump Head Bolts

Referring to Figure 5.21, reposition the pump head andinstall the four (4) M6-1.0 x 35 cap screws.

Tighten the M6-1.0 cap screws to the torque value specifiedin the Torque Chart, found on Figure 5.2 (Exploded View) atthe beginning of this chapter.

NOTE: Torque the outlet check valve caps at thistime, if not done previously.

Oil Fill

As shown in Figure 5.22, set the pump on its head. Pour inthe specified amount of 80W90 oil through the port used bythe engine crankshaft.

Verify that the oil level reaches the upper lip of the pistonhousing, as shown in Figure 5.23. The pump can now beinstalled onto the engine.

For specific recommendations for oil type and capacity,please refer to the table given in Part 1, at the beginning ofthis section.



Item Name


2 M6 lock washer

3 Piston & unloader housing attached toengine adapter

Figure 5.23 — Oil Level

Figure 5.22 — Oil FillFigure 5.21 — Head Bolt Installation

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Part 5 - Troubleshooting

1. Water leakage between pump head andpiston housing.

a. Head bolts improperly torqued.

b. Damaged head.

c. Missing or damaged o-rings

a. Torque head bolts.

b. Replace head.

c. Install new o-rings.

2. Water leaks from pressure outconnector.

a. Connector not properly sealed.

b. Damaged connector.

a. Seal with teflon tape and tightenproperly.

b. Replace bad connector.

6. Detergent does not mix with spray. a. Nozzle is in “high pressure” mode.

b. Chemical suction line is not submerged.

c. Chemical suction strainer or line isclogged.

a. Reset nozzle to “low pressure”.

b. Insert line into fluid.

c. Clean or replace strainer or line.

3. Oil leak between motor and motoradapter.

a. Defective or missing motor adapter o-ring.

b. Motor adapter cap screws not tightenedproperly.

a. Install new o-ring.

b. Tighten to correct torque.

4. Oil leak between motor adapter andpiston/unloader housing.

a. Missing or bad o-ring seal.

b. Cap screws not tightened properly.

a. Install new o-ring seal.

b. Tighten to correct torque.

5. Pump does not produce pressure,exhibits erratic pressure, chatters, or hasa low water volume.

a. Nozzle is set to low pressure mode.

b. Incorrect spray nozzle is used.

c. Spray nozzle is obstructed.

d. Water Inlet blocked

e. Inadequate water supply to pump.

f. Water supply hose kinked or leaking.

g. Clogged inlet hose strainer.

h. Water supply too hot.

i. Worn or defective pump.

a. Reset nozzle to high pressure.

b. Replace with correct nozzle.

c. Clear obstruction from nozzle.

d. Clear inlet.

e. Provide sufficient water supply.

f. Relieve kinking or repair leak.

g. Clean strainer.

h. Reduce inlet water temperature tobelow 140oF.

i. Disassemble and repair pump.

Problem Possible Cause Corrective Action

small frame gas pump

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