Mercury 40, 4 (GNAT 2 CYL.) (9075839 THRU 9256980) Parts & Diagrams

🔎 Mercury 40, 4 (GNAT 2 CYL.) Reference Library — Exploded parts diagrams (14 diagrams), specifications, common issues, and maintenance checklist.

The Mercury 40, 4 (GNAT 2 CYL.) is a 4-Stroke, Inline 4-Cylinder, EFI, SOHC outboard motor. Commonly used on jon boats, pontoons, and mid-size utility craft.

Quick Reference Specifications

Specification	Value
Engine Type	4-Stroke, Inline 4-Cylinder, EFI, SOHC
Horsepower	40 HP
Displacement	995 cc
Bore x Stroke	65 mm x 75 mm
Spark Plug (Type & Gap)	NGK IZFR6F-11
Engine Oil Capacity	3.0 L (3.17 quart)
Recommended Engine Oil	SAE 25W-40 Mercury FourStroke Oil
Gear Case Oil Capacity	440 mL (14.9 fl oz)
Idle Speed (in gear)	700 ± 50 RPM (in gear)
Full Throttle RPM Range	5500-6000
Fuel	Unleaded Gasoline, 87 Octane min.

Always verify specifications against your owner's manual for your specific serial number range.

Common Issues & Recommended Parts

Below are common maintenance scenarios for the Mercury 40, 4 (GNAT 2 CYL.):

Water Pump / Overheating: If the tell-tale stream is weak or absent, the water pump impeller likely needs replacement. Inspect annually or every 100 hours. → Recommended: Water Pump Impeller Kit
Engine Oil / Maintenance Light: 4-stroke engines require regular oil and filter changes. Use marine-grade oil rated for your engine. Change every 100 hours or annually. → Recommended: Oil Filter, Engine Oil
Fuel Injector Issues (EFI models): Rough idle or misfires may indicate clogged fuel injectors. Use fuel stabilizer and clean injectors periodically. → Recommended: Fuel Injector, Fuel Filter
Gear Case Oil Leak: Check lower unit seals if gear oil appears milky (water contamination). Replace seals and gaskets during lower unit service. → Recommended: Lower Unit Seal Kit, Drain Plug Gaskets
Anode Corrosion: Inspect sacrificial anodes regularly, especially in saltwater. Replace when 50% depleted to protect against galvanic corrosion. → Recommended: Zinc/Aluminum Anode Kit

Parts Diagrams & OEM Part Numbers

Expand the sections below to view detailed exploded parts diagrams and find the exact OEM replacement components for your Mercury 40, 4 (GNAT 2 CYL.).

▶BOTTOM COWL (32 parts)

Ref	OEM Part #	Part Name
-	27-77586A78	GASKET SET
1	2154-7603	BOTTOM COWL (SERIAL #9141799 AND UP)
2	714933	MOLDING, BOTTOM COWL (2" - 6-1/2" - 15")
3	70455	COVER, BOTTOM COWL
4	10-69079	SCREW, COVER TO BOTTOM COWL (7/16")
5	86055T	HANDLE, SHIFT SERIAL Comment: #9210546 AND UP
6	86056A1	SHAFT, SHIFT Comment: #9210546 AND UP
7	10-69560	SCREW, SHIFT HANDLE TO SHAFT (1 1/4") Comment: #9210546 AND UP
8	13-26996	LOCKWASHER, SHIFT HANDLE SCREW Comment: #9210546 AND UP
9	66414	CAM, SHIFT DETENT
10	17-25905	ROLL PIN, CAM TO SHIFT SHAFT
11	23-26856	BUSHING, SHIFT SHAFT
12	25-16524	"O" RING, SHIFT SHAFT
13	72733	ARM, SHIFT
14	10-72734	SET SCREW, SHIFT ARM (5/16")
15	18-210711	COTTER PIN, SHIFT SHAFT
16	24-39627	SPRING, DETENT
17	39601	PLATE, DETENT SPRING
18	10-25764	SCREW, DETENT SPRING TO BOTTOM COWL (1/2")
19	27-92874	GASKET, DRIVE SHAFT HOUSING/BOTTOM COWL
20	69602	TRIM COVER Comment: SERIAL #9141798 AND BELOW
21	10-75827	SCREW, TRIM COVER TO BOTTOM COWL Comment: SERIAL #9141798 AND BELOW
22	53-72168	"E" RING, RETAINER
23	70393	RETAINER, STARTER HANDLE Comment: (SERIAL #9190380 AND UP)
24	19-74258	PLUG, BOTTOM COWL - FUEL ADAPTOR
25	70462	ARM, LATCH CRANK
26	24-70459	SPRING, LATCH CRANK
27	75263	CRANK, FRONT LATCH
28	13-34632	WAVE WASHER, LATCH HANDLE
29	92798	HANDLE, LATCH BOTTOM COWL
30	17-38489	ROLL PIN, LATCH HANDLE TO CRANK
31	74802	STOP, SHIFT ARM

▶CARBURETOR ASSEMBLY (16 parts)

Ref	OEM Part #	Part Name
1	89977A2	CARBURETOR ASSEMBLY
2	1395-6043	RETAINER, JET (.041)
4	1395-8155	FUEL BOWL
6	1395-5898	FLOAT
7	1395-5904	SPRING, FLOAT
9	1395-4805	SCREEN, FILTER
10	1395-5900	NOZZLE
14	1395-5896	SHAFT, CHOKE
15	1395-5905	SPRING, CHOKE RETURN
16	1395-5897	VALVE, CHOKE
17	1395-5902	SCREW, VALVE
18	1395-5894	SHAFT, THROTTLE
19	1395-5903	SPRING, THROTTLE RETURN
20	1395-8670	VALVE, THROTTLE
22	1395-6103	SPRING, IDLE NEEDLE
23	1395-6618	REPAIR PARTS KIT

▶CLAMP AND SWIVEL BRACKET ASSEMBLY (31 parts)

Ref	OEM Part #	Part Name
1	1479-7291A1	CLAMP BRACKET ASSEMBLY (PORT) Comment: WASHER ATTACHED WITH A SCREW
2	1478-7289A1	CLAMP BRACKET ASSEMBLY (STARBOARD) Comment: WASHER ATTACHED WITH A SCREW
3	10-77190A4	THUMB SCREW ASSEMBLY Comment: WASHER ATTACHED WITH A SCREW
4	78971	HANDLE, THUMB SCREW Comment: WASHER ATTACHED WITH A SCREW
5	17-78970	GROOVE PIN, THUMB SCREW Comment: WASHER ATTACHED WITH A SCREW
6	12-73719	WASHER, THUMB SCREW Comment: WASHER ATTACHED WITH A SCREW
6A	10-768042	SCREW, THUMB SCREW WASHER Comment: WASHER ATTACHED WITH A SCREW
7	10-96917	SCREW, CLAMP BRACKET Comment: (SERIAL #9213206 AND UP)
8	12-68920	WASHER, CLAMP BRACKET STUD OR SCREW
9	11-8M0204726	NUT, CLAMP BRACKET STUD OR SCREW
10	16-68925	STUD, CLAMP BRACKET
11	13-26992	LOCKWASHER< CLAMP BRACKET STUD
12	11-29598	NUT, CLAMP BRACKET STUD
13	17-68929A2	TILT PIN ASSEMBLY
14	71369	COVER, EXHAUST RELIEF Comment: USED ON EARLY MODELS ONLY
15	10-48408	SCREW, EXHAUST RELIEF COVER (1/2") Comment: USED ON EARLY MODELS ONLY
16	1477-7400A2	SWIVEL BRACKET ASSEMBLY
17	10-69067	SCREW, SWIVEL BRACKET (1 3/8")
17A	22-8M0169589	GREASE FITTING, SWIVEL BRACKET
17B	19-77633Q	LUBRICAP, GREASE FITTING
18	10-71105A1	THUMB SCREW ASSEMBLY
19	76110A1	TILT LEVER ASSEMBLY Comment: (SERIAL #9141799 AND UP)
20	24-68932	SPRING, TORSION - PORT
21	68968	ROD, REVERSE LOCK
22	18-25191	COTTER PIN, REVERSE LOCK ROD
23	68972	LEVER, REVERSE LOCK
24	24-73124	SPRING, TORSION - STARBOARD
25	22-8M0169589	GREASE FITTING (NOT USED WITH REF. #14)
25A	19-77633Q	LUBRICAP, GREASE FITTING
26	24-62143	SPRING, TILT PIN
27	23-75065	SPACER, REVERSE LOCK ROD

▶CRANKSHAFT, PISTON AND CONNECTING ROD (21 parts)

Ref	OEM Part #	Part Name
-	27-77586A78	GASKET SET
1	458-5549	CRANKSHAFT
2	626-5547A5	CONNECTING ROD ASSEMBLY
3	10-72455	SCREW, CONNECTING ROD
4	14-72454	TAB WASHER, CONNECTING ROD SCREW
5	29-68944	NEEDLE BEARING, CONNECTING ROD
6	68953A1	LINER ASSEMBLY, CONNECTING ROD - CRANKPIN
8	31-68949	ROLLER BEARING, CONNECTING ROD - PISTON PIN
9	758-8076A2	PISTON ASSEMBLY
10	40-68950	LOCK RING, PISTON
11	39-70175A12	PISTON RING ASSEMBLY
12	26-30530	OIL SEAL, CRANKSHAFT - UPPER
13	31-78099	ROLLER BEARING, CRANKSHAFT - UPPER
14	71841	RING, CRANKSHAFT
15	30-69389	BALL BEARING, CRANKSHAFT - LOWER
16	53-68952	RETAINING RING, BALL BEARING - LARGE
17	53-27275	RETAINING RING, BALL BEARING - SMALL
18	26-77494	OIL SEAL, CRANKSHAFT
19	25-62706	"O" RING, CRANKSHAFT
20	70786A1	COUPLING ASSEMBLY, CRANKSHAFT
21	26-76266	SEAL, COUPLING

▶CYLINDER BLOCK AND CRANKCASE ASSEMBLY (33 parts)

Ref	OEM Part #	Part Name
-	27-77586A78	GASKET SET
1	862-7713A2	BLOCK AND CRANKCASE ASS'Y Comment: SERIAL #9210546 AND UP
2	16-728091	STUD, POWERHEAD (1 5/8") Comment: SERIAL #9210546 AND UP
3	17-8M0084726	PIN, CYLINDER BLOCK
5	16-20353	STUD, REED BLOCK AND CARBURETOR
6	22-56800	PLUG, PIPE - CYLINDER BLOCK
7	10-70732	SCREW, CRANKCASE TO CYLINDER BLOCK (2")
8	10-28635	SCREW, CRANKCASE TO CYLINDER BLOCK (5/8")
9	10-28667	SCREW, CRANKCASE TO CYLINDER BLOCK (1")
10	68953A1	LINER ASSEMBLY, CYLINDER BLOCK
12	29-71840	NEEDLE BEARING, CENTER MAIN
13	77585	COVER, EXHAUST MANIFOLD Comment: SERIAL #9210546 AND UP
14	27-77586	GASKET, EXHAUST MANIFOLD COVER Comment: SERIAL #9210546 AND UP
15	10-32228	SCREW, EXHAUST MANIFOLD COVER (5/8") Comment: SERIAL #9210546 AND UP
16	1027-5546	COVER, CYLINDER BLOCK
17	27-68942	GASKET, CYLINDER BLOCK COVER
18	10-32228	SCREW, CYLINDER BLOCK COVER (5/8")
19	27-68941	GASKET, BLOCK TO BOTTOM COWL
20	11-8M0207775	NUT, POWERHEAD STUDS
22	32-9938779	HOSE, BLEED
23	22-56759	FITTING ADAPTOR
24	21-64871A2	CHECK VALVE ASSEMBLY, CRANKCASE
25	69498	REED BLOCK
26	27-70415	GASKET, CRANKCASE TO REED BLOCK
27	34-69499A1	REED ASSEMBLY
28	34-69500	REED STOP
29	10-28430	SCREW, REED AND REED STOP (1/4")
30	27-70416	GASKET, REED BLOCK TO ADAPTOR
31	70420	ADAPTOR, CARBURETOR TO REED BLOCK
32	79746	BRACKET, CABLE MOUNTING Comment: (SERIAL #9210596 AND UP)
33	10-69022	SCREW, BRACKET TO ADAPTOR (1/2")
34	10-20055	SCREW, CABLE MOUNTING BRACKET (7/16")
35	74777	FILLER BLOCK, REED BLOCK TO CRANKCASE Comment: (EARLY MODELS)

▶DRIVE SHAFT HOUSING ASSEMBLY (13 parts)

Ref	OEM Part #	Part Name
1	1580-6673A2	DRIVE SHAFT HOUSING ASSEMBLY Comment: SERIAL #9210596 AND UP
2	16-75321	STUD, DRIVE SHAFT HOUSING (LONG SHAFT)
3	10-79953Q04	SCREW, GREASE FILLER
4	12-191833	WASHER, GREASE FILLER SCREW
5	32-75308	WATER TUBE (LONG SHAFT)
6	26-36556	SEAL, WATER TUBE
7	23-13127	WASHER, WATER TUBE SEAL
8	68976	CLAMP, CO-PILOT
9	88669	MOUNT Comment: RUBBER - DRIVE SHAFT HOUSING (BOTTOM)
10	23-74308	BUSHING, RUBBER MOUNT
11	98496A1	BRACKET ASSEMBLY, STEERING ARM
12	10-68918	SCREW, STEERING ARM BRACKET (1")
13	94909	BEARING BLOCK, DRIVE SHAFT (LONG SHAFT)

▶FLYWHEEL, STATOR AND MANUAL STARTER (48 parts)

Ref	OEM Part #	Part Name
1	247-7933A2	FLYWHEEL ASSEMBLY
2	28-20094	KEY, FLYWHEEL DRIVE
3	12-20553	WASHER, FLYWHEEL
4	11-8M0204726	NUT, FLYWHEEL
5	339-5566A5	STATOR ASSEMBLY
6	10-66707	SCREW, STATOR TO MOUNTING BRACKET (7/8")
7	339-5590A1	COIL ASSEMBLY (3 3/8" AND 4 3/8" LEADS)
8	54-59538	CLIP, COIL RETAINING
9	54-65927	CLIP, COIL RETAINING
10	86-69348	TERMINAL BLOCK, STATOR
10A	13-58308	LOCKWASHER, TERMINAL BLOCK
11	10-22654	SCREW, LEADS TO TERMINAL BLOCK (3/8")
12	10-69347	SCREW, TERMINAL BLOCK TO STATOR (5/8")
13	11-46438	NUT, TERMINAL BLOCK SCREW
14	70426A3	TRIGGER ASSEMBLY
17	70414	LINK ROD, TRIGGER TO SPARK LEVER
18	11-68219	NUT, ADJUSTING LINK ROD
19	33973	SWIVEL BOLT, LINK ROD
20	70428	BRACKET, STATOR MOUNTING
21	10-25764	SCREW, STATOR MOUNTING BRACKET (7/16")
22	70422	LEVER, SPARK
23	10-62802	SCREW, ADJUSTING - SPARK LEVER (1 1/8")
24	11-21923T	NUT, ADJUSTING SCREW
25	24-70418	SPRING, THROTTLE LEVER
26	70424	THROTTLE LEVER
27	70429	THROTTLE CAM
28	10-38055	SCREW Comment: THROTTLE CAM TO THROTTLE LEVER (5/8")
29	12-8M0204666	WASHER, THROTTLE CAM SCREW (7/8")
30	10-38515	SCREW, SHOULDER (7/8")
31	12-69056	WASHER, SHOULDER SCREW
32	24-70167	SPRING, STARTER REWIND
33	75764	BRACKET ASSEMBLY, STARTER REWIND
34	10-37571	SCREW, BRACKET TO CYLINDER BLOCK (1/2")
34A	12-30164	WASHER, BRACKET TO CYLINDER BLOCK SCREW
35	77568	STARTER SHEAVE
36	50-90892A2	STARTER ROPE ASSEMBLY (INCLUDES 2 RIVETS)
37	70396	HANDLE, STARTER ROPE
38	70394	CAP, STARTER HANDLE
39	75764A2	PINION, STARTER REWIND
39A	12-30164	WASHER, PINION
40	24-70288	SPRING, PINION
41	72697	RETAINER, PINION SPRING
42	24-77511	SPRING, TORSION - PINION
43	77512	HOLDER, SPRING
44	23-78894	SPACER, SPRING HOLDER Comment: (SERIAL #9189790 AND UP)
45	10-70181	SCREW, SPRING RETAINER (5/8")
46	12-8M0204666	WASHER, SPRING RETAINER
47	17-70180	RIVET, STARTER SHEAVE

▶FUEL TANK, FUEL LINES AND CARBURETOR (41 parts)

Ref	OEM Part #	Part Name
-	27-77586A78	GASKET SET
1	1248-8083A2	FUEL TANK (SERIAL #9191589 AND UP)
2	10-70298	SCREW, VENT - FUEL CAP
3	12-8M0204663	WASHER, VENT SCREW
4	36-78573A1	CAP, FUEL SERIAL Comment: SERIAL #9191589 AND UP
5	27-78577	GASKET, FUEL CAP Comment: SERIAL #9191589 AND UP
6	12-38255	WASHER, FUEL CAP
7	24-22227	SPRING, FUEL CAP
8	12-71055	WASHER, FUEL CAP
9	18-210711	PIN, FUEL CAP - RING
10	752373	CHAIN, FUEL CAP
11	24-85767	SPRING, FUEL CAP - RETAINING Comment: SERIAL #9191589 AND UP
12	27-78578	GASKET, FUEL TANK TO COWL Comment: SERIAL #9191589 AND UP
13	78579	BRACKET, FUEL TANK AND IGNITION COIL Comment: SERIAL #9191589 AND UP
14	10-37571	SCREW, BRACKET TO CYLINDER BLOCK (1/2")
15	11-859124	NUT, BRACKET SCREW
16	75689A1	STRAP ASSEMBLY, FUEL TANK ATTACHING
16A	10-26668	SCREW Comment: STRAP ASSEMBLY TO FUEL TANK BRACKET
17	22-70997	FITTING, FUEL TANK (FILTER)
18	54-68725	CLAMP, FUEL LINE TO FITTING
19	32-8M0108355	FUEL LINE, FUEL TANK TO VALVE (8")
20	54-68424	CLAMP, FUEL LINE ATTACHING
21	20-70555	VALVE Comment: FUEL SHUT OFF (SERIAL #9191588 AND BELOW)
22	32-8M0108355	FUEL LINE Comment: VALVE TO CARBURETOR (4" AND 1-1/2")
23	22-19688	FITTING, CARBURETOR TO FUEL LINE (90 DEG.)
24	89977A2	CARBURETOR
25	27-70417	GASKET, CARBURETOR MOUNTING
26	70557	CHOKE CABLE (SQUARE SHOULDER)
27	77999	SPACER, CHOKE KNOB - INNER Comment: USE WITH ROUND SHOULDERED CHOKE
28	78000	SPACER, CHOKE KNOB - OUTER Comment: USE WITH ROUND SHOULDERED CHOKE
29	11-78045	NUT, LOCKING - CHOKE CABLE
30	86874	KNOB, CHOKE CABLE
31	12-8M0204649	WASHER, CARBURETOR STUD
32	11-36069	NUT, CARBURETOR STUD
33	35-76934	FUEL FILTER
34	78049	LEVER, IDLE ADJUSTMENT
35	78046	LINK, IDLE ADJUSTMENT
36	78048	SHAFT, IDLE ADJUSTMENT
38	23-78047	SLEEVE, IDLE ADJUSTMENT
40	11-78045	NUT, CHOKE KNOB
41	76623	BRACKET, FUEL TANK (LONG SHAFT)

▶GEAR HOUSING ASSEMBLY (DRIVE SHAFT) (34 parts)

Ref	OEM Part #	Part Name
-	27-77586A78	GASKET SET
1	1648-7381A1	GEAR HOUSING ASSEMBLY, BASIC
2	16-75321	STUD, GEAR HOUSING (7 1/4") - LONG SHAFT
3	16-68928	STUD, WATER PUMP (2 1/4')
4	16-70741	STUD, WATER PUMP (1 1/2")
5	31-23101	ROLLER BEARING, GEAR HOUSING - LOWER
6	68978	COUPLING, DRIVE SHAFT/PINION
7	31-69496	ROLLER BEARING, GEAR HOUSING - UPPER
8	43-68981	PINION GEAR
9	31-68945	THRUST BEARING, PINION GEAR
10	12-71557	WASHER, THRUST BEARING
11	45-75310	DRIVE SHAFT (LONG SHAFT)
12	28-8M0032835	KEY, IMPELLER DRIVE
13	27-68939	GASKET, WATER PUMP - LOWER
14	46-90844A1	WATER PUMP HOUSING ASSEMBLY
15	26-897153	OIL SEAL, WATER PUMP
16	70977T	INSERT, WATER PUMP
17	12-8M0204666	WASHER, WATER PUMP
18	25-74138	QUAD SEAL, WATER PUMP
19	47-89980	IMPELLER
20	68955	FACE PLATE, WATER PUMP
21	46-95965A2	WATER PUMP COVER ASSEMBLY
22	26-30913	OIL SEAL, WATER PUMP COVER
23	23-13127	WASHER, WATER TUBE SEAL
24	26-36558	SEAL, WATER TUBE
24A	23-31792T	SLEEVE, WATER TUBE GUIDE
25	25-30526	RING, RUBBER - DRIVE SHAFT
26	12-30164	WASHER, WATER PUMP STUDS
27	11-859124	NUT, WATER PUMP STUDS
28	75307	SHIFT SHAFT (LONG SHAFT)
29	10-28653	SCREW, VENT - GEAR HOUSING (1/4")
30	19643	WASHER, VENT SCREW
31	10-79953Q04	SCREW, GREASE FILLER
32	12-191833	WASHER, GREASE FILLER SCREW

▶GEAR HOUSING ASSEMBLY (PROPELLER SHAFT) (23 parts)

Ref	OEM Part #	Part Name
-	27-77586A78	GASKET SET
1	1648-7381A1	GEAR HOUSING ASSEMBLY
33	11-20696	NUT, PROPELLER SHAFT
34	12-73672	WASHER, PROPELLER SHAFT
35	43-68980	DRIVE GEAR
36	24-91813	SPRING, CLUTCH
37	15-69516A1	SHIM ASSEMBLY, BALL BEARING
38	30-70894	BALL BEARING, DRIVE GEAR
39	11-69515	NUT, DRIVE GEAR
40	44-68982	PROPELLER SHAFT
41	75816	SPACER, PROPELLER SHAFT Comment: SERIAL #9210546 AND UP
42	99210A1	BEARING CARRIER ASSEMBLY Comment: SERIAL #9210546 AND UP
43	31-21145	ROLLER BEARING Comment: SERIAL #9210545 AND BELOW
44	26-98309	OIL SEAL Comment: SERIAL #9210546 AND UP
45	75812	COVER, GEAR HOUSING Comment: SERIAL #9210546 AND UP
46	25-68935	"O" RING, BEARING CARRIER
47	28-32003	KEY, BEARING CARRIER
48	12-68923	WASHER, GEAR HOUSING COVER Comment: SERIAL #9141798 AND BELOW
49	70588	THRUST HUB, FORWARD
50	48-86903A1	PROPELLER ASSEMBLY
51	70589	THRUST HUB, AFT
52	11-82670911	NUT, PROPELLER
53	11-82670911	NUT, DRIVE SHAFT HOUSING STUD

▶MISCELLANEOUS PARTS/ACCESSORIES (1 parts)

Ref	OEM Part #	Part Name
-	75311A1	CONVERSION KIT Comment: (SHORT SHAFT TO LONG SHAFT)

▶STEERING HANDLE ASSEMBLY (19 parts)

Ref	OEM Part #	Part Name
1	11099A1	BOOT ASSEMBLY, HANDLE
2	70382	GRIP, HANDLE
3	70383	ARM, HANDLE
4	12-31433	WASHER, HANDLE
5	53-70384	RETAINING RING, HANDLE
6	70386	PULLEY, STEERING CABLE
7	70385	SHAFT, HANDLE
7A	84-70671A1	HARNESS ASSEMBLY, STOP SWITCH
8	70389A2	BRACKET ASSEMBLY, HANDLE
9	10-37978	SCREW, HANDLE BRACKET (3/4")
10	70390	RETAINER, CABLE
11	85-708571	INSULATOR, CABLE
12	23-70391	BUSHING, HANDLE BRACKET
13	11-73784	NUT, HANDLE BRACKET
14	92791	CABLE, THROTTLE ADVANCE
15	92791	CABLE, THROTTLE RETARD
16	11-21825	NUT, THROTTLE CABLE
17	12-37998	WASHER, THROTTLE CABLE
18	32-9912688	SLEEVE, STOP SWITCH HARNESS

▶SWITCH BOX AND IGNITION COIL (14 parts)

Ref	OEM Part #	Part Name
1	339-6222A8	SWITCH BOX ASSEMBLY
2	10-45218	SCREW, SWITCH BOX GROUND (3/8")
3	10-22523	SCREW, SWITCH BOX (3/4")
3A	23-26731	SPACER, SWITCH BOX SCREW (EARLY MODELS)
4	12-8M0204666	WASHER, SWITCH BOX SCREW
5	54-63153	"J" CLIP, SWITCH BOX LEAD
6	33-813472	SPARK PLUG (USE IN BELGIUM AND CANADA)
7	33-813472	SPARK PLUG (USE IN UNITED STATES)
8	300-8M0166172	IGNITION COIL ASSEMBLY
10	11-45076	NUT, IGNITION COIL TERMINAL
11	76254	COIL COVER
12	10-76502	SCREW, COIL COVER (1 7/8")
13	61990	STA-STRAP, SWITCH BOX LEADS
14	5790811	SLEEVE, SWITCH BOX LEADS

▶TOP COWL (15 parts)

Ref	OEM Part #	Part Name
1	2155-6654	TOP COWL (SERIAL #9191589 AND UP) Comment: DOES NOT INCLUDE DECALS
2	74139	HOOK, TOP COWL - REAR
3	10-45742	SCREW, HOOK TO COP COWL (3/8")
4	11-8M0204718	NUT, HOOK SCREW
5	70461	CATCH, TOP COWL - FRONT
6	10-69570	SCREW, CATCH TO COP COWL (3/4")
7	78634	SOUND BOX (SERIAL #9141799 AND UP)
7A	22-390721	PLUG, SOUND BOX
8	10-52195	SCREW, SOUND BOX TO CARBURETOR (1/2")
9	12-20192	WASHER, SOUND BOX SCREW
10	27-70289	GASKET, SOUND BOX Comment: NOT USED ON LATER MODELS
11	70292	COVER, SOUND BOX Comment: NOT USED ON LATER MODELS
12	19-824928001	PLUG, SOUND BOX Comment: NOT USED ON LATER MODELS
13	10-95700	SCREW, COVER TO SOUND BOX (1/2") Comment: NOT USED ON LATER MODELS
14	10-72415	SCREW, SOUND BOX TO COVER (1")

100-Hour / Annual Service Checklist

Regular maintenance keeps your Mercury 40, 4 (GNAT 2 CYL.) running reliably season after season. Most of these tasks can be performed with basic tools and the factory service manual.

Replace water pump impeller and inspect wear plate
Change engine oil and oil filter (check drain plug washer)
Replace spark plugs and check ignition timing
Drain and refill lower unit gear oil; inspect for water contamination
Inspect fuel lines, primer bulb, and fuel filter for deterioration
Check and replace sacrificial anodes (zinc or aluminum)
Inspect propeller for damage; check shaft seal and cotter pin
Check valve clearance (refer to service manual for specifications)
Lubricate all grease points (steering, tilt tube, shift linkage)
Inspect control cables and throttle/shift linkage for smooth operation

Pro Tip: Always flush the engine with fresh water after saltwater use — even a quick 10-minute flush significantly extends component life.
Pro Tip: Use fuel stabilizer in the tank before winter storage, and fog the cylinders to prevent internal corrosion during extended periods of non-use.

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Mercury 40, 4 (GNAT 2 CYL.) (9075839 THRU 9256980) Parts & Diagrams

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