RedMax GZ25N Workshop Manual

S4810-0006

R

Workshop Manual

STRATO CHARGED ENGINE

GZ25N

Applicable Model Name:

1.Brushcutters BCZ2500S/BCZ2500SU

2.Long Reach Trimmer LRTZ2500

3.Short Reach Trimmer SRTZ2500

4.Pole Saw PSZ2500

5.Reciprocator SGCZ2500S

6.Sweeper RMSZ2500

7.Hand Held Edger HEZ2500S

July 2000

CONTENTS

BRUSHCUTTERS BCZ2500S/BCZ2500SU

1. OUTLINE OF STRATO-CHARGED ENGINE		................................. 2
1-1	Special Features .................................................................................................................................	2
1-2	Principle of Operation .........................................................................................................................	3
1-3	Construction (Developed Drawing) .....................................................................................................	4
2. SPECIFICATIONS AND TECHNICAL DATA ..................................		5
3. OUTLINE DRAWING ......................................................................		6
4. MAINTENANCE SPECIFICATIONS ...............................................		7
4-1	Engine Block .......................................................................................................................................	7
4-2	Carburetor ..........................................................................................................................................	8
4-3	Ignition System ...................................................................................................................................	8
4-4	Fastening Specifications ......................................................................................................................	8
4-5	Sealant and Lubricant Specifications ..................................................................................................	8
5. SPECIAL TOOLS ............................................................................		9
6. SERVICE GUIDE ..........................................................................		10
6-1	GENERAL PRECAUTIONS ..............................................................................................................	10
6-2	Removing of Clunch Shoe ...............................................................................................................	11
6-3	Mounting of Clutch Shoe ...................................................................................................................	11
6-4	Removing of Rotor ............................................................................................................................	11
6-5	Removing Recoil Pulley ....................................................................................................................	12
6-6	Assembling of lgnition Coil ................................................................................................................	12
6-7 Installing of Spark Plug ....................................................................................................................		12
6-8	Laying of Switch Cable ....................................................................................................................	13
6-9	Fitting of Plug Cap ............................................................................................................................	13
6-10	Removing Piston Pin .........................................................................................................................	13
6-11 Installing of Piston 14
6-12 Assembling of Piston Pin Circlip ........................................................................................................		14
6-13 Direction of Setting Cylinder Gasket .................................................................................................		14
6-14 Positioning of Lead Air Intake Tube ....................................................................................................		15
6-15 Assembling of Cylinder Plate .............................................................................................................		15
6-16 Setting of Insulator Gasket .................................................................................................................		15
6-17 Mounting of Reed Valve .....................................................................................................................		16
6-18 Removal of Clutch Drum ....................................................................................................................		16
6-19 Assembling Cluch Drum ....................................................................................................................		17
7. CARBURETOR .............................................................................		18
7-1	Construction .....................................................................................................................................	18
7-2	Function and Operation of Throttle Valve ..........................................................................................	18
7-3	Specifications ....................................................................................................................................	19
7-4	Composition and Inspection ..............................................................................................................	20
8. TROUBLE SHOOTING .................................................................		21
8-1	Engine does not start ........................................................................................................................	21
8-2	Stalled during Operation ...................................................................................................................	21
8-3	Engine cannot be stopped ................................................................................................................	22
8-4 Lack of output power or unstable revolution .....................................................................................		22

3

1. OUTLINE OF STRATO-CHARGED ENGINE

STRATO CHARGED ENGINE GZ25N

1-1 Special Features

Unlike the conventional 2-stroke engine scavenging system, the Strato-charged Engine scavenges burnt gas by the stratified lead air scavenging method. By creating a stratified air layer between burnt gas and the air-fuel mixture, this system significantly reduces exhaust of unburned air-fuel mixture.

Difference to the conventional 2-stroke engine is its very simple construction applying a new carburetor for independent intake of the air and the air-fuel mixture, an insulator, lead air intake tubes, and reed valves, etc.

By the stratified lead air scavenging system, the Strato-charged Engine reduces unburned air-fuel mixture exhaust to about 1/3 of the conventional 2-stroke engine level.

By optimizing the combustion chamber design, ignition plug position, and ignition timing, lean burn operation became possible.

By combining with the stratified lead air scavenging system, pollutant contained in the exhaust was reduced and fuel consumption was reduced by 30% without reducing the power.

		Unit : g/HP•h (g/kwh)
		400
		(544)
		280
		(381)
171.2
(232)
		139.1	5.3
		(189)
			(7.2)
54	49.5
(73)
	(67)		1.5	1.0
			(2.0)
				(1.3)
THC + NOx		CO	PM

Current Engine

Tier 2 regulation

Strato-Changed Engine

As the catalytic converter is not applied, exhaust gas temperature increase due to the catalytic reactive heat does not occur so that the engine heat load does not increase. Therefore, same level of durability and reliability with the conventional engines are assured.

A large size silencer and a muffler were employed and the noise level was reduced by 5 dB(A) compared to the conventional 2-stroke engines.

Insulator

Lead Air Intake Tube (each side)

Reed Valve (each side)

Carburetor

2

1. OUTLINE OF STRATO-CHARGED ENGINE

1-2 Principle of Operation

STRATO CHARGED ENGINE GZ25N

Major difference of the Strato-charged Engine to the conventional 2-stroke engine is that as illustrated on the following drawing, there are lead air intake tubes which are connected to the scavenging port via reed valves.

Due to crankcase depression during the piston upstroke

As piston proceeds to downstroke after the top dead center,

As piston proceeds to upstroke after the bottom dead center,

(intake stroke) to the top dead centre, air-fuel mixture is charged

a scavenging port starts to open and lead air in the scavenging

burnt gas in the cylinder is pushed out through the exhaust

to the crankcase and lead air is charged to the scavenging

port moves into the cylinder earlier than the air-fuel mixture.

port by lead air. Therefore, direct exhaust of air-fuel mixture

ports though the reed valves.

is almost non.

Lead Air

Burnt Gas

Burnt Gas

Air

Air-Fuel Mixture

Scavenging Port

Reed Valve

Air-Fuel Mixture

Exhaust Port

Exhaust Port

Lead Air

Crankcase

Air-Fuel Mixture

Reed Valve Assy

Lead Air Intake Tube

Lead Air

Air

Scavenging Port

Air-Fuel Mixture

Carburetor

Air-Fuel Mixture

3

1. OUTLINE OF STRATO-CHARGED ENGINE

STRATO CHARGED ENGINE GZ25N

1-3 Construction (Developed Drawing)

Parts in the frames are exclusively designed for the Strato-charged Engine.

• Reciprocator SGCZ2500S

	Spark Plug
	Reed Valve
Lead Air Intake Tube	Cylinder
Carburetor	Reed Valve
	Insulator
	Lead Air Intake Tube

•Brushcutters BCZ2500S/BCZ2500SU

•Long Reach Trimmer LRTZ2500

•Short Reach Trimmer SRTZ2500

•Pole Saw PSZ2500

•Sweeper RMSZ2500

•Hand Held Edger HEZ2500S

•Split Boom Trimmer : EXZ2500S

4

2. SPECIFICATIONS AND TECHNICAL DATA

STRATO CHARGED ENGINEGZ25N

Item			Unit	Specifications		Remarks
Engine				GZ25N
Engine Type				Air cooled 2-stroke single cylinder
				piston valve gasoline engine
Cylinder Bore x Stroke			mm (in.)	ø34 x 28 (1.339 x 1.102)
Displacement			cc (cu.in.)	25.4 (1.6)
Effective Compression Ratio				8.0
Fuel				Mixture of 87 octane or above unleaded		Use JASO FC
				gasoline and RedMax 2-cycle engine oil		or ISO EDG
				(ratio 50 :1) or quality oil for air cooled		grade 2-cycle
				2-cycle engines (ratio 32:1).		engine oil.
Carburetor		Type		Diaphragm Rotary valve
		Model		Walbro WYA-1B
Starting Method				Recoil starter
Ignition System				CDI with automatic timing advance
				system.
Ignition Timing			°/ rpm	35 / 7000
Spark Plug				NGK CMR7A
Stopping Method				Primary coil short-circuiting
Cooling System				Forced Air Cooling
Air Cleaner				Dry Type
Output Axle Rotation Direction				Counterclockwise		(View from
						PTO)
Clutch Type				Automatic Centrifugal Clutch
				(Sintered Clutch Shoe)
Overall Size				Engine GZ25N for	Engine GZ25N2 for
				exept SGCZ2500S	SGCZ2500S
		Length	mm (in.)	271 (10.67)	188 (7.40)
		Width	mm (in.)	223 (8.78)	223 (8.78)
		Height	mm (in.)	248 9.76	248 9.76
Dry Weight			kg (lbs.)	3.1 6.8	2.8 6.2
Fuel tank Capacity			lit. (fl,oz)	0.65 22.0
Operating Speed			rpm	6000	10000
Idling Speed			rpm	3000 ±200
Clutch Engagement Speed			rpm	4000 ±200
No-Load Max Speed			rpm	10000		With Standard
						Head
Max Output			HP(kW) / rpm	1.2 (0.9) / 7500
Max Torque			kg•m(in.lbs) / rpm	0.12 (10.4) / 6500
Full Load Fuel Consumption			g/HP.h(g/kW.h)	330 (449)
				5

3. OUTLINE DRAWING

STRATO CHARGED ENGINEGZ25N

Unit : mm (in.)

Carburetor

Air Cleane

	Fuel Cap
	Fuel Tank
	122 (4.80)
	223 (8.78)
Plug Cap
	Fan Cover
Fan Cover	Recoil Starter
	)
	9.76
	(
	248
	)
	4.45
	(
	113
168 (6.61)	7.85
	(0.31)

238(9.36)

271 (10.67)

GZ25N for

BCZ2500S, BCZ2500SU,

LRTZ2500, SRTZ2500,

PSZ2500, RMSZ2500,

HEZ2500S and EXZ2500S.

Engine Cover

Muffler

Tank Guard

248 (9.76)

113 (4.45)

85 (3.35)

155(6.10) 188 (7.40)

GZ25N2 for

SGCZ2500S.

6

4. MAINTENANCE SPECIFICATIONS

4-1 Engine Block

STRATO CHARGED ENGINEGZ25N

Maintenance Item							Standard	Limit	Measuring	Remarks
									Instrument
Cylinder
	Compression						8.7(124)	5.5(78)	Compression
	kg/cm2 (psi)								Gauge
	Bore						ø 34(1.339)	Peel off of plating or	Cylinder
	mm(in.)							expose of base met	Gauge
Piston
	Piston dia.					ø33.96(1.3370)		ø33.86(1.3331)	Micrometer	At right angle to
	mm(in.)						ø33.975(1.3376)			piston pin.
	Piston Ring Groove Width mm(in.)						1.2(0.047)	1.3(0.051)	Thickness Gauge
	Piston Pin Hole Bore				mm(in.)		ø8(0.3150)	ø8.04(0.3165)	Cylinder Gauge
	Clearance between					0.025(0.0010)		0.15(0.0059)	Micrometer /
	Piston & Cylinder			mm(in.)			0.065(0.0026)		Cylinder Gauge
	Clearance between Groove					0.04 (0.0016)		0.1(0.0039)	Thickness
	and Piston Ring			mm(in.)			0.08(0.0031)		Gauge
	Fitting between Piston Pin &					0.005T(0.00020T)		0.05L(0.0020L)	Micrometer /
	Piston Pin Hole			mm(in.)			0.011L(0.00043L)		Cylinder Gauge
Piston Ring
	End Gap	mm(in.)				0.1(0.0038)		0.5(0.0197)	Thickness Gauge	Measure at
							0.3(0.0118			cylinder skirt.
	Width mm(in.)					1.2(0.0472)		1.1(0.0433)	Micrometer
Piston Pin
	Diameter	mm(in.)					ø8(0.315)	ø7.98(0.314)	Micrometer	No stepwear is allowed
Connecting Rod
	Small End Bore			mm(in.)			ø11 (0.433)	ø11.05(0.435)	Cylinder Gauge
	Clearance between Small End Piston					0	0.021(0.0008)	0.045(0.0018)	Micrometer /
	Pin & Needle Bearing			mm(in.)					Cylinder Gauge
	Clearance between Large End Crank					0.005(0.0002)		0.05(0.0020)	Micrometer /
	Pin & Needle Bearing			mm(in.)		0.028(0.0011)			Cylinder Gauge
	Parallelness of Large/Small						–	0.15/100	Mandrel
	End Bores		mm(in.)						Dial Gauge
Crankshaft
	Diameter at Main Bearing					ø12(0.4724)		ø11.97(0.4713)	Micrometer
	(MAG, PTO)		mm(in.)
	Diameter at Oil Seal						ø12(0.472)	ø11.09(0.469)	Micrometer
	(MAG, PTO)		mm(in.)
	Diameter at Clutch Drum					ø12(0.4724)		ø11.97(0.4713)	Micrometer
	Bearing ( PTO)			mm(in.)
	Eccentricity		mm(in.)				–	0.07(0.028)	Dial Gauge /	Adjust or exchange
									Centre Support
	Width between crank webs				mm(in.)		22	21.9 22.1	Micrometer
	Axial Play	mm(in.)					–	0.5(0.020)	Thickness Gauge
	Main Bearing (Ball Bearing)						–	Flutter, irregular
								noise generated
Clutch Drum
	Bore at Bearing			mm(in.)		ø12 (0.472)		ø12.05(0.474)	Cylinder Gauge
	Bore at Drum		mm(in.)				ø54(2.126)	ø54.6(2.150)	Vernia Calipers

7