Graco GMx 7900 User manual

824128
Rev. E
Related Manuals
Operation 308867. . . . . . . . . . . . . . . . . . . . . . . . . .
Displacement Pump 308798. . . . . . . . . . . . . . . . .
Spray Gun 307614. . . . . . . . . . . . . . . . . . . . . . . . .
Spray Tip 308644. . . . . . . . . . . . . . . . . . . . . . . . . . .
PC Board 308919. . . . . . . . . . . . . . . . . . . . . . . . . .
Drain Valve Kit 308961. . . . . . . . . . . . . . . . . . . . . .
Tool Box Kit 308817. . . . . . . . . . . . . . . . . . . . . . . .
PATENTS PENDING
9035A
INSTRUCTIONS-REPAIR
INSTRUCTIONS
KEEP FOR REFERENCE.
Read this and all related manuals for
important warnings and instructions.
GMxr7900
Airless Paint Sprayer
3300 psi (227 bar, 22.7 MPa ) Maximum Working Pressure
GMx 7900
Model Series Description
824630 B Hi-Boy with tool box and Lo-Boy
suction/drain line kit
Table of Contents
Warnings and Cautions 2. . . . . . . . . . . . . . . . . . . . . . . . .
Component Identification and Function 3. . . . . . . . . . . .
Maintenance 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Troubleshooting 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Repair
Rollers 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Drive Housing 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cam Follower Bearings 8. . . . . . . . . . . . . . . . . . . . . . .
Pinion Assembly/Rotor/Field/Shaft/Clutch 9. . . . . . . .
Clamp 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Clutch Housing 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Engine 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pressure Control 13. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Displacement Pump 15. . . . . . . . . . . . . . . . . . . . . . . . .
Parts
Pinion Assembly 17. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sprayer 18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pressure Control 20. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lo-Boy Suction Set Kit 22. . . . . . . . . . . . . . . . . . . . . . .
Dimensions 23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Technical Data 23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Phone Number 23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sherwin-Williams Warranty 24. . . . . . . . . . . . . . . . . . . . .
The SHERWIN–WILLIAMS COMPANY, CLEVELAND, OHIO 44115
ECOPYRIGHT 1999, GRACO INC.

8241282
Warnings and Cautions
Warning Symbol
WARNING
This symbol alerts you to the possibility of serious
injury or death if you do not follow the instructions.
Caution Symbol
CAUTION
This symbol alerts you to the possibility of damage to
or destruction of equipment if you do not follow the
instructions.
Fluid injection is a serious injury! If high pressure fluid pierces
your skin, the injury might look like “just a cut”. But it is a serious
wound! Get immediate medical attention.
To help prevent injection, always:
DEngage trigger safety latch when not spraying.
DPoint gun away from yourself or anyone else.
DRelieve pressure before checking or repairing any leak.
DRelieve pressure when you turn off the sprayer or stop spraying.
DDo not use components rated less than system Maximum
Working Pressure
Never allow children to use this unit. If you are injured using this
equipment, get immediate medical treatment.
Fire and explosion can occur when spraying or flushing flammable
fluid in an area where air circulation is poor and flammable vapors
can be ignited by an open flame or sparks.
To help prevent a fire and explosion:
DUse outdoors or in an extremely well ventilated area.
DDo not use 1,1,1–trichloroethane, methylene chloride, other
halogenated hydrocarbon solvents or fluids containing such
solvents in pressurized aluminum equipment. Such use could
result in a chemical reaction, with the possibility of explosion.
DRemove, extinguish or unplug all ignition sources;
tape wall switch. Do not smoke in spray area.
DNever fill fuel tank while the engine is running or hot.
DGround Sprayer, object being sprayed, paint and solvent pails.
DHold gun firmly to side of a grounded pail when triggering into pail.
DUse only conductive airless paint hose.
DNever run engine in inclosed area.
WARNING

824128 3
Component Identification and Function
9034A
Fig. 1
S
U
W
T
X
V
P
AB
C
E
F
G
H
J
K
M
N
L
Model 824630
R
D
APressure Control Switch ON/OFF, enables/disables clutch function and pressure control
BPressure Adjusting Knob Controls fluid outlet pressure
CAir Cleaner* Filters air entering the carburetor
DFuel Tank* Uses 86 octane unleaded gasoline
EMuffler* Reduces noise of internal combustion
FSpark Plug Cable* Routes electrical current to spark plug
GFuel Shutoff Lever* On/off lever to regulate fuel flow from gasoline tank to carburetor
HChoke* Enriches air/gasoline mixture for cold starting
JThrottle Lever* Adjusts engine speed for large or small orifice spray tips
KEngine Switch* Enables/disables engine operation
LSecondary Fluid Outlet Second hose and spray gun is connected here
MPressure Control Controls clutch cycling to maintain fluid pressure.
NPrimary Fluid Outlet Hose and spray gun is connected here
PEngine* 4–cycle gasoline engine
RClutch Housing Transfers power from engine to drive assembly
SDrive Housing Transfers power from clutch to displacement pump
TDisplacement Pump Provides fluid to be sprayed through spray gun
UFluid Filter Filters fluid between source and spray gun
VGrounding Clamp and Wire Grounds sprayer system
WPail Hanger Provides a hanger for paint pail
XDrain Valve Relieves fluid pressure when open
*For more detailed explanations of these controls, refer to the Honda Engines Owner’s Manual; supplied

8241284
Maintenance
WARNING
INJECTION HAZARD
The system pressure must be manually
relieved to prevent the system from
starting or spraying accidentally. Fluid
under high pressure can be injected through the
skin and cause serious injury. To reduce the risk of
an injury from injection, splashing fluid, or moving
parts, follow the Pressure Relief Procedure
whenever you:
Dare instructed to relieve the pressure,
Dstop spraying,
Dcheck or service any of the system equipment,
Dor install or clean the spray tip.
Pressure Relief Procedure
1. Lock gun trigger safety.
2. Turn engine ON/OFF switch to OFF.
3. Move pressure control switch to OFF and turn
pressure control knob fully counterclockwise.
4. Unlock trigger safety. Hold metal part of gun firmly
to side of grounded metal pail, and trigger gun to
relieve pressure.
5. Lock gun trigger safety.
6. Open pressure drain valve. Leave valve open until
ready to spray again.
If you suspect that the spray tip or hose is completely
clogged, or that pressure has not been fully relieved
after following the steps above, VERY SLOWLY
loosen tip guard retaining nut or hose end coupling to
relieve pressure gradually, then loosen completely.
Now clear tip or hose.
CAUTION
For detailed engine maintenance and specifications,
refer to separate Honda Engines Owner’s Manual,
supplied.
DAILY: Check engine oil level and fill as necessary.
DAILY: Check hose for wear and damage.
DAILY: Check gun safety for proper operation.
DAILY: Check pressure drain valve for proper opera-
tion.
DAILY: Check and fill the gas tank.
AFTER THE FIRST 20 HOURS OF OPERATION:
Drain engine oil and refill with clean oil. Reference
Honda Engines Owner’s Manual for correct oil viscos-
ity.
WEEKLY: Remove air filter cover and clean element.
Replace element, if necessary. If operating in an
unusually dusty environment: check filter daily and
replace, if necessary.
Replacement elements can be purchased from your
local HONDA dealer.
WEEKLY: Check level of TSL in displacement pump
packing nut. Fill nut, if necessary. Keep TSL in nut to
help prevent fluid buildup on piston rod and premature
wear of packings.
AFTER EACH 100 HOURS OF OPERATION:
Change engine oil. Reference Honda Engines Owner’s
Manual for correct oil viscosity.
SPARK PLUG: Use only BPR6ES (NGK) or
W20EPR–U (NIPPONDENSO) plug. Gap plug to
0.028 to 0.031 in. (0.7 to 0.8 mm). Use spark plug
wrench when installing and removing plug.

824128 5
Troubleshooting
WARNING
INJECTION HAZARD
To reduce risk of serious injury, including fluid injection or splashing in eyes or on skin, or injury from
moving parts, always follow Pressure Relief Procedure Warning, page 4, before checking, adjust-
ing, cleaning or shutting down sprayer.
PROBLEM CAUSE SOLUTION
Engine won’t start Engine switch is OFF Turn engine switch ON
Engine is out of gas Refill gas tank. Honda Engines Owner’s Manu-
al.
Engine oil level is low Try to start engine. Replenish oil, if necessary.
Honda Engines Owner’s Manual.
Spark plug cable is disconnected or damaged Connect spark plug cable or replace spark
plug
Cold engine Use choke
Fuel shutoff lever is OFF Move lever to ON position
Oil is seeping into combustion chamber Remove spark plug. Pull starter rope 3 or 4
times. Clean or replace spark plug. Try to start
engine. Keep sprayer upright to avoid oil seep-
age.
Engine operates, but dis-
p
lacement
p
um
p
does not
Pressure control switch is OFF Turn pressure control switch ON.
p
l
acemen
t
pump
d
oes no
t
operate Pressure setting is too low Turn pressure adjusting knob clockwise to
increase pressure.
Fluid filter (318) is dirty Clean filter. Page 20.
Tip or tip filter is clogged Clean tip or tip filter. Manual 307614.
Displacement pump piston rod is stuck due to
dried paint
Repair pump. Manual 308798.
Roller bearings are worn or damaged Replace connecting rod. Page 7.
Drive housing is worn or damaged Replace drive housing. Page 7.
Electrical power is not energizing clutch field Check wiring connections. Page 11.
Reference control board diagnostics. Page 14.
With pressure control switch ON and pressure
turned to MAXIMUM, use a test light to check
for power between clutch terminals on control
board.
Remove black clutch wires from control board
and measure resistance across wires. At 70_
F, the resistance must be between 1.7 ±0.2Ω; if
not, replace clutch coil 241121.
Have pressure control checked by authorized
Graco dealer.
Clutch is worn or damaged Replace clutch. Page 9.
Pinion assembly is worn or damaged Repair or replace pinion assembly. Page 9.

8241286
PROBLEM CAUSE SOLUTION
Pump output is low Strainer (31) is clogged Clean strainer
Piston ball (25) is not seating Service piston ball. Manual 308798.
Piston packings are worn or damaged Replace packings. Manual 308798.
O-ring (227) in displacement pump is worn or
damaged
Replace o-ring. Manual 308798.
Intake valve ball is not seating properly Clean intake valve. manual 308798.
Engine speed is too low Increase throttle setting. Manual 308867.
Clutch is worn or damaged Replace clutch. Page 9.
Pressure setting is too low Increase pressure. Manual 308867.
Fluid filter (318), tip filter or tip is clogged or
dirty
Clean filter. Manual 308867 or 307614.
Large pressure drop in hose with heavy
materials
Use larger diameter hose and/or reduce overall
length of hose. Use of more than 100 ft of 1/4
in. hose significantly reduces performance of
sprayer. Use 3/8 in. hose for optimum perfor-
mance (50 ft minimum).
Excessive paint leakage into
throat packing nut
Throat packing nut is loose Remove throat packing nut spacer. Tighten
throat packing nut just enough to stop leakage.
Throat packings are worn or damaged Replace packings. Manual 308798.
Displacement rod is worn or damaged Replace rod. Manual 308798.
Fluid is spitting from gun Air in pump or hose Check and tighten all fluid connections.
Reprime pump. Manual 308867.
Tip is partially clogged Clear tip. Manual 307614.
Fluid supply is low or empty Refill fluid supply. Prime pump. Manual
308867. Check fluid supply often to prevent
running pump dry.
Pump is difficult to prime Air in pump or hose Check and tighten all fluid connections.
Reduce engine speed and cycle pump as
slowly as possible during priming.
Intake valve is leaking Clean intake valve. Be sure ball seat is not
nicked or worn and that ball seats well. Reas-
semble valve.
Pump packings are worn Replace pump packings. Manual 308798.
Paint is too thick Thin the paint according to the supplier’s
recommendations
Engine speed is too high Decrease throttle setting before priming pump.
Manual 308867.
Clutch squeaks each time
clutch engages
Clutch surfaces are not matched to each other
when new and may cause noise
Clutch surfaces need to wear into each other.
Noise will dissipate after a day of run time
Engine stalls Engine speed is to slow DIncrease throttle setting
DAdjust engine speed at no load to 3750 –
3850 rpm
Fluid filter is clogged Relieve pressure and clean filter
Too much pump friction (new pump) Reduce pressure to 3000 psi until pump wears
in
Spark plug wire is loose Reconnect wire

824128 7
Rollers
Removal
1. Relieve pressure;page 4.
2. Fig. 2. Remove six cap screws (10) lock washers
(9) and cover assembly (24).
Note: A screw driver may be needed to pry off
cover assembly.
3. Remove dowel pins (97) and rollers (98)
Installation
1. Install rollers (98) and dowel pins (97)
2. Install cover assembly (24) with six lock washers
(9) and cap screws (10). Fig. 2
9033A
10
9
97
98
20
9
99
24
Drive Housing
Removal
1. Relieve pressure;page 4.
2. Fig. 2. Remove six cap screws (10) lock washers
(9) and cover assembly (24).
3. Fig. 3. Remove two screws (99) and washers (9).
4. Remove four cap screws (10) lock washers (9)
from drive housing (20).
5. Lightly tap around drive housing (20) to loosen
drive housing. Pull drive housing straight off pinion
housing. Be prepared to support gear cluster (18),
which may also come out.
Fig. 3 9032A
20
9
99
9
10
20h
20g
18
82 83
B
1
1Apply remaining grease to these areas
Installation
1. Liberally apply bearing grease (supplied with
replacement gear cluster) to gear cluster (18),
washers (82) and (83) and to areas called out by
note 1. Use full 0.68 pint (0.32 liter) of grease for
GMx 7900.
2. Place bronze colored washer (83) and silver
colored washer (82) onto drive housing (20). Install
gear cluster (18) through washers (83) and (82).
3. Place bronze colored washer (20g) and silver
colored washer (20h) on shaft protruding from
large shaft of drive housing (20). Align gears and
push new drive housing straight onto pinion hous-
ing and locating pins (B).
4. Install two washers (9) and screws (99).
5. Install four lock washers (9) and cap screws (10)
into drive housing (20).
6. Install cover assembly (24) with six lock washers
(9) and cap screws (10).

8241288
Cam Follower Bearings
Removal
1. Relieve pressure;page 4.
2. Fig. 16. Cycle pump piston rod (222) to lowest
position. Turn engine off.
3. Fig. 4. Remove six cap screws (10), lock washers
(9) and cover assembly (24).
Note: A screw driver may be needed to pry off
cover assembly.
4. Remove four dowel pins (97) and rollers (98).
5. From front, drive out pump pin (101) with a screw
driver.
6. Remove two retainer rings (20d).
7. Remove cam follower plate (20b).
Note: Two 1/2 in. x 13 bolts may be
needed to remove cam follower plates.
8. Remove two cam follower bearings (20c).
Installation
1. Install two cam follower bearings (20c).
2. Install cam follower plate (20b).
3. Install two retainer rings (20d).
4. Drive in pump pin (101) until it engages with pump
pin retaining clip (20a).
5. Install four rollers (98) and dowel
pins (97).
6. Install cover assembly (24) with six lock washers
(9) and cap screws (10).
Fig. 4
9047A
101
24
10
9
97
98
20c
20
20b
20d
20a

824128 9
Pinion Assembly/Rotor/Field/Shaft/Clutch
Removal
If pinion assembly (19) is not removed from clutch
housing (5), do 1. through 4. Otherwise, start at 5.
1. Relieve pressure;page 4.
2. Disconnect field cable (X) from pressure control
and engine lead.
9027A
Fig. 5
X
Bottom View
3. Fig. 6. Remove five screws (26) and lockwashers
(17) and pinion assembly (19).
26
17
26
17
Fig. 6 9029A
19
4. Fig. 7. Place pinion assembly (19) on bench with
rotor side up.
5. Remove four screws (72) and lockwashers (17).
Install two screws in threaded holes (E) in rotor.
Alternately tighten screws until rotor comes off.
Fig. 7
E
72
17
9030A
6. Fig. 8. Remove retaining ring (19e).
7. Tap pinion shaft (19d) out with plastic mallet.
Fig. 8
19e
19d
9030A
8. Fig.9. Use an impact wrench or wedge something
between armature (4a) and clutch housing to hold
engine shaft during removal.
9. Remove four screws (16) and lockwashers (17).
10. Remove armature (4a).
Fig. 9
16
17
4a
9028A

82412810
Pinion Assembly/Rotor/Field/Shaft/Clutch
Installation
1. Fig. 10. Lay two stacks of two dimes on smooth
bench surface.
2. Lay armature (4a) on two stacks of dimes.
3. Press center of clutch down on bench surface.
Fig. 10
4a
8705A
0.12 ±.01 in. (3.0 ±.25 mm)
4. Install armature (4a) on engine drive shaft.
5. Install four screws (16) and lockwashers (17) with
torque of 125 in-lb.
6. Fig. 8. Tap pinion shaft (19d) in with plastic mallet.
7. Install retaining ring (19e) with beveled side facing
field (Y).
8. Fig. 7. Place pinion assembly on bench with rotor
side up.
9. Apply locktite to screws. Install four screws (16)
and lockwashers (17). Alternately torque screws
to 125 in-lb until rotor is secure. Use threaded
holes to hold rotor.
10. Fig. 6. Install pinion assembly (19) with five screws
(10) and lockwashers (9).
11. Fig. 5. Connect field cable (X) to pressure control
and engine lead.
Clamp
Removal
1. Fig. 11. Loosen two screws (16) on clamp (8),
2. Push screwdriver into slot in clamp (8) and remove
clamp.
Installation
1. Fig. 11. Install engine shaft key (7).
2. Tap clamp (8) on engine shaft (A) with plastic
mallet.
3. Press clamp (8) onto engine shaft (A). Maintain
dimension shown note 2 in Fig. 11. Chamfer side
must face engine.
Check dimension: Place rigid, straight steel bar (B)
across face of clutch housing (5). Use accurate
measuring device to measure distance between
bar and face of clamp. Adjust clamp as necessary.
Torque two screws (16) to 125 ±10 in-lb (14 ±1.1
Nm). Fig. 11
16
5
B
03483
1
3
2
Face of clutch housing
1.812 ±.010 in. (46.02 ±.25 mm)
Torque to 125 ±.10 in-lb (14 ±1.1 Nm)
1
2
3
7
8
A
4Chamfer this side
4