Stihl FS 25-4 User Manual Download Page 15

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- Remove the pushrods -

see 6.4.

- Remove the flywheel

see 7.2.

•

Take out the screws.

- Remove the cover.

•

Pull out pin (1).

•

Remove the cam followers (2).

Install in the reverse sequence.

- Thoroughly clean the sealing

face on the cylinder and cover.

- Apply thin coating of sealant to

cylinder -

see 14.2.

Important: Follow manufacturer’s
instructions.

- Tighten down screws on cover

to 3 Nm.

- Install the flywheel -

see 7.2.

- Install the pushrods

see 6.4.

- Remove the cam followers

see 6.5.

•

Pull out pin (1).

•

Remove the cam gear (2).

- Set piston to T.D.C.:

Slot (1) in crankshaft points up.

•

Install cam gear so that marks
(2) line up and the marked
tooth (3) is in alignment with
the slot in the crankshaft.

Important: The marks must not
move out of position while cam
gear is being fitted.

•

Install the cam followers
-

see 6.5.

- Drain engine oil -

see 6.2.

- Remove the fuel tank

see 11.6.

•

Take out the screws.

- Remove the cover.

•

Take out screw (1).

•

Remove the support plate (2).

•

Remove the diaphragm.

FS 25-4, 65-4

Summary of Contents for FS 25-4

Page 1: ... Replacing 29 9 5 2 Adjusting 30 10 AV System 30 11 Fuel System 32 11 1 Air Filter 32 11 2 Carburetor 32 11 2 1 Leakage Test 32 11 2 2 Removing Installing 33 11 2 3 Adjusting Idle Speed 34 11 3 Tank Vent 35 11 4 Pickup Body 35 11 5 Fuel Hoses 36 11 6 Fuel Tank 37 12 Shaft 38 12 1 Bike Handle 38 12 2 Loop Handle 38 12 3 Drive Shaft Flexible Liner 39 12 4 Drive Tube 40 13 Cutting Tool Drive 41 13 1 ...

Page 2: ...es which have been intro duced since publication of this service manual Technical informa tion bulletins also supplement the parts list until a revised edition is issued The special servicing tools men tioned in the descriptions are listed in the last chapter of this ma nual Use the part numbers to identify the tools in the STIHL Special Tools manual The manual lists all special servicing tools cu...

Page 3: ...ment Pawls Single pawl system Reserve pull on rope rotor min 1 2 turn Starter rope diameter 3 mm Clutch Centrifugal clutch with press fitted linings Clutch engages at 4 200 200 rpm Valve clearance Inlet 0 12 0 02 mm Exhaust 0 15 0 02 mm Oil capacity 0 1 l 100 cm3 Oil grade SAE 15W 40 3 2 Fuel System Carburetor Diaphragm carburetor Carburetor leakage test at gauge pressure 8 kPa 0 8 bar Function of...

Page 4: ...gap 0 6 0 7 mm 3 4 Gearhead Type Spiral toothed bevel gear drive Gear ratio 1 1 4 Bearings Deep groove ball bearings Lubrication STIHL gear lubricant 0781 120 1117 1118 capacity 7 g 3 5 Special Accessories 3 5 1 For User Full harness Safety glasses Transport guard for Metal cutting tools 4119 717 3005 STIHL gear lubricant 80 g tube 0781 120 1109 STIHL gear lubricant 80 g tube 0781 120 1117 4 FS 25...

Page 5: ...and exhaust Free length of valve springs 23 40 mm 22 50 mm Valve stem outside diameter Inlet 3 985 mm 3 900 mm Exhaust 3 950 mm 3 880 mm Valve guide inside diameter 4 000 mm 4 060 mm Clearance between valve stem and guide Inlet 0 015 0 048 mm 0 098 mm Exhaust 0 050 0 083 mm 0 120 mm Valve head diameter Inlet 12 5 mm 13 5 mm Exhaust 12 0 mm Clutch lining 2 0 mm 1 0 mm FS 25 4 FS 65 4 3 6 Dimensions...

Page 6: ...p control handle drive tube loop handle 2 0 Spline screw IS M5x16 AV sleeve drive tube clamp screw 5 5 Spline screw IS M5x12 Clamp control handle drive tube 2 0 Spline screw IS M5x16 Clamp drive tube harness 4 5 Spline screw IS M5x30 Control handle bike handle 2 0 Spline screw IS M6x25 Clamp loop handle 4 5 Screw plug M11x10 Gearhead 8 5 Plastoform screw IS P4x16 Control handle handle moldings 1 0...

Page 7: ...ow to carburetor Dry No spark or only a weak spark Compression in order Compression too low Fill up with fuel and try starting again Check fuel line and fuel filter for blockages Faulty carburetor diaphragm or float needle valve replace carburetor Replace carburetor Change spark plug and repeat the spark test Check ignition lead for damaged insulation and leakage current Check ignition coil Check ...

Page 8: ...Check compression Normal Start engine according to instructions Dirty Abnormal Abnormal Dirty Abnormal Abnormal Clean replace air filter element Clean spark plug and adjust electrode gap Replace spark plug If fuel line is kinked or pinched fit a new one Tighten loose carburetor nuts Examine spacer flange for damage and install properly Clean replace filter Replace carburetor Check adjust valve cle...

Page 9: ... looseness or air entering through spacer flange Normal Check correct function of carburetor Normal Start engine according to instructions Dirty Abnormal Abnormal Abnormal Clean replace air filter element Clean spark plug and adjust electrode gap Replace spark plug If fuel line is kinked or pinched fit a new one Tighten loose carburetor nuts Examine spacer flange for damage and install properly Re...

Page 10: ...es or signs of excessive wear Important If there are signs of serious wear on the inside diameter fit a new clutch drum see 13 2 Block piston with locking screw see 7 2 Take out the collar screws 1 Remove the clutch shoes 2 Twist the clutch shoes and detach the spring Important Clutch shoes must always be replaced in pairs Attach spring to clutch shoes Fit the washers Fit clutch shoes so that the ...

Page 11: ... On bike handle machine install the control handle Fit the shroud Note Check and adjust valve clea rance only when engine is cold Remove the rewind starter Remove the air filter see 11 1 Pull off the spark plug boot Take ignition lead out of the retainer Slacken off nut 1 Pull throttle cable 2 with short circuit wire 3 and washer 4 out of retainer 6 Engine 6 2 Checking Adjusting 6 1 Valve Clearanc...

Page 12: ...er 2 Remove the gasket Remove clutch housing with dri ve tube see 12 4 Rotate flywheel until blade recess 1 lines up with the projection 2 on the cam gear cover piston at T D C Note If the exhaust valve opens while you are turning the flywheel to T D C rotate flywheel counter clockwise until the recess and projection line up again Insert feeler gauge 1 between rocker arm and valve stem Inlet valve...

Page 13: ...surface Unscrew the dipstick and wipe it with a clean cloth Push the dipstick into filler neck as far as stop but do not screw it home Remove the dipstick and check the oil level If oil level is low top up with fresh engine oil to edge of filler neck Screw dipstick home and tighten down firmly Changing Unscrew the dipstick Tip the engine to one side to drain oil into a suitable container Note Obse...

Page 14: ...s of screws Remove the valve cover see 6 1 Set piston to T D C both rocker arms relieved Pull out pin 1 Remove rocker arms 2 To replace slacken off nut 1 and take out the adjusting screw 2 Remove the pushrods Assemble in the reverse sequence Pushrods must locate properly in the adjusting screws Adjust valves see 6 1 6 3 Exhaust Muffler 6 4 Rocker Arms Pushrods 14 FS 25 4 65 4 ...

Page 15: ...nstall the pushrods see 6 4 Remove the cam followers see 6 5 Pull out pin 1 Remove the cam gear 2 Set piston to T D C Slot 1 in crankshaft points up Install cam gear so that marks 2 line up and the marked tooth 3 is in alignment with the slot in the crankshaft Important The marks must not move out of position while cam gear is being fitted Install the cam followers see 6 5 Drain engine oil see 6 2...

Page 16: ...uence shown 1 to 4 to 3 Nm then finally tighten to 7 Nm in same sequence Remove cover over diaphragm see 6 7 Take out the screws Take away the lower half of the crankcase Unscrew dipstick if necessary Remove grommets if necessary Check to see if oil return bores are blocked Blow clear with compressed air if necessary Thoroughly clean sealing faces on both halves of crankcase Apply thin coating of ...

Page 17: ...d oil scraper ring with oil Fit piston ring so that their gaps are offset 120 degrees Important Ring gaps must not be in line with piston pin bore Rotate cam gear so that the marks 1 are in alignment Carefully push the piston into the cylinder Note The piston rings and the oil scraper ring are compressed as they are eased into the tapered cylinder Turn the crankshaft so that the slot 2 points towa...

Page 18: ... and replace parts as necessary Check free length of valve springs 3 replace springs if ne cessary Assemble in the reverse sequence Important Do not mix up inlet and exhaust valves Valve spring retainer must engage properly in groove on valve stem Remove the valves see 6 10 Remove the cam gear see 6 6 Remove the muffler see 6 3 Remove the carburetor see 11 2 2 Take out the screws 1 Remove the heat...

Page 19: ...lectronic breakerless ignition system basically consists of an ignition module 1 and flywheel 2 The ignition module accommoda tes all the components required to control ignition timing There are two electrical connec tions on the coil body 1 the high voltage output with ignition lead 1 2 the connector tag 2 for the short circuit wire Accurate testing of the ignition module is only possible with so...

Page 20: ...ine starting and running behavior Remove the shroud see 6 1 Remove the clutch housing with drive tube see 12 4 Disconnect short circuit wire from ignition module Remove ignition lead from the retainers Take out the screws Remove the ignition module Slip feeler gauge 0 4 mm between the arms of the ignition module and the flywheel magnet poles Press the ignition module against the feeler gauge and t...

Page 21: ...s or ot her damage If you find any damage install a new flywheel Installing the flywheel Important Clean the stub of the crankshaft and the flywheel hub bore with a standard commercial solvent based degreasant which contains no chlorinated or halogenated hydrocarbons see 14 2 Check correct position of key Fit flywheel in position screw on the nut and tighten it down to 15 Nm Remove locking screw f...

Page 22: ...rt see Standard Repairs Trouble shooting handbook Remove rewind starter and take off the machine support Relieve tension of rewind spring Note The rewind spring will not be under tension if the starter rope is broken Pull out the starter rope about 20 cm and hold the rope rotor steady Locate starter rope in the notch in the rope rotor Use starter rope to turn rotor clockwise until spring is no lon...

Page 23: ...andard grip Pull rope out of starter grip untie the knot and slip the grip off the rope Thread starter rope through the new grip Secure end of rope with one of the special knots shown Pull starter rope back so that the knot is snugly seated in the starter grip ElastoStart Pry cap out of starter grip Pull rope out of starter grip Thread end of new starter rope through the underside of the star ter ...

Page 24: ... straighten it out Hold the starter grip firmly to keep the rope tensioned Let go of the rope rotor and slowly release the starter rope so that it can rewind properly Note The rewind spring is correct ly tensioned when the starter grip sits firmly in the rope guide bush without drooping to one side If this is not the case tension the spring by one additional turn When the starter rope is fully ext...

Page 25: ...l as shown Insert punch in bores in starter cup and hold steady Slip a screwdriver between the punches and unscrew the starter cup Remove fanwheel from stub of crankshaft Assemble in the reverse sequence Block starter cup with punches and screwdriver Tighten down starter cup to 8 Nm via flywheel nut 8 6 Starter Cup Fanwheel FS 25 4 65 4 25 ...

Page 26: ...rlock lever off the peg Remove the torsion spring Take the throttle trigger 1 with torsion spring 2 and throttle cable 3 off the peg Disconnect throttle cable from trigger Assemble in the reverse sequence Attach the throttle cable then position torsion spring as shown and push its long arm into the slot The interlock lever must be behind the throttle trigger Check correct positions of throttle cab...

Page 27: ...e molding Assemble in the reverse sequence Engage contact spring correctly in groove of collar screw Use screwdriver 1 5910 890 2301 to remove screw Push guard 2 forward Warning To avoid risk of electric shock do not start the unit while the control handle is open Remove screws with screwdriver 1 5910 890 2301 Remove handle molding Remove torsion spring 9 2 Contact Springs Detent Spring in Control...

Page 28: ...peg Remove contact spring from interlock lever Assemble in the reverse sequence Check positions of throttle cable 1 contact spring 2 protective tube 3 and insulator 4 Tighten screws to 1 0 Nm Remove the interlock lever see 9 3 Pull slide control off the handle molding Remove screws from clamps Take handle molding off the dri ve tube Remove torsion spring from peg 9 4 Slide Control Loop Handle 28 F...

Page 29: ... 11 1 Take throttle cable off the con tact spring see 9 2 Pull short circuit wire off the connector tag Disconnect throttle cable nipple 1 from slotted pin 2 on throttle lever Slacken off nut 1 Pull throttle cable 2 out of hol der Remove short circuit wire 3 from the throttle cable On bike handle take throttle cable out of retainers Assemble in the reverse sequence Adjust throttle cable see 9 5 2 ...

Page 30: ...loser to housing Rotate sleeve counterclockwise to move lever away from housing Lock adjusting sleeve with nut 1 after completing adjustment Install the air filter see 11 1 The anti vibration AV connection between the engine and drive tube consists of a rubber element installed in the clutch housing Remove the drive tube see 12 4 Remove the shroud see 6 1 Take out the screws Remove the clutch hous...

Page 31: ...rew 2 if necessary Pull the AV sleeve 3 off the installing tool Pull the rubber element off the AV sleeve Push the rubber element larger diameter 1 first onto the AV sleeve until the inner groove 2 engages the annular rib 3 Coat rubber element with a lubricant e g washing up liquid Push the rubber element into clutch housing as far as stop so that slot 1 is opposite the straight side 2 of the clut...

Page 32: ... foam filter in fresh engine oil and then squeeze out surplus oil Install foam filter Engage lugs on filter cover in filter housing Swing filter cover up so that it snaps into position Troubleshooting chart see Standard Repairs Trouble shooting handbook Important In the event of trouble with the carburetor or the fuel supply system always check and clean the tank vent see 11 3 The carburetor can b...

Page 33: ...1 The inlet needle is not sealing foreign matter in valve seat or sealing cone of inlet needle is damaged or inlet control lever sticking 2 The metering diaphragm is damaged After completing test open the vent screw and pull the fuel hose off the elbow connector Push the fuel hose onto the elbow connector Install the air filter see 11 1 Remove the air filter see 11 1 Pull both fuel hoses off the e...

Page 34: ... in the reverse sequence Install new gasket and sealing ring Tighten down nuts to 5 0 Nm Check the air filter replace if necessary Start the engine and allow it to warm up Adjust engine idle speed with the idle speed screw Turn clockwise to increase rpm Turn counterclockwise to reduce rpm Note If you use a tachometer note that there is an ignition spark on each crankshaft revolution 11 2 3 Adjusti...

Page 35: ... valve 6 in fresh gasoline If the valve is damaged fit a new fuel filler cap Insert cap 3 in the valve body Slip sealing ring 4 over the val ve body Fit cap 1 on valve body and push it home until it snaps into position Screw on the fuel filler cap The diaphragm pump draws fuel out of the tank and into the carburetor via the fuel hose Any impurities mixed with the fuel are retained by the pickup bo...

Page 36: ...ses off the carburetor see 11 2 2 Take fuel hoses out of the retainer Ease the grommet out of the fuel tank Pull out fuel hoses with pickup body Squeeze ends of hose clip 1 together and push it down the hose Pull the pickup body 2 off the fuel hose Pull the fuel hoses out of the grommet Install in the reverse sequence Pull fuel hoses into the grommet so that the distance a is 113 121 mm and b is 1...

Page 37: ...of the fuel tank Pull out fuel hoses with pickup body Unscrew filler cap 2 with remove together with cap retainer Assemble in the reverse sequence Inspect grommets in crankcase and fit new ones if necessary Position fuel tank so that the lugs 1 engage the grommets 2 Inspect grommet in support plate and fit new grommet if necessary with the wider flange facing the fuel tank 11 6 Fuel Tank FS 25 4 6...

Page 38: ...ed the grip will twist on the tube Always leave it to dry for a while after fitting Push the grip into position so that the longer ends see arrows point toward the gearhead at an angle of 7 15 degrees to the shaft Assemble all parts in the reverse sequence Loop handle without barrier bar Unscrew the nuts 1 Remove lower clamp 2 Remove screws 1 Remove the loop handle 2 and upper clamp 3 Reassemble i...

Page 39: ... out of the drive tube Note If the shaft has turned blue fit a new one Coat the drive shaft with STIHL gear lubricant 0781 120 1109 see 14 2 before installation Important Apply the grease uniformly and thinly to the whole drive shaft Do not pump grease directly into the drive tube Push the drive shaft into the dri ve tube Push the drive shaft into the dri ve tube until dimension A is 23 mm If nece...

Page 40: ...with bike handle take throttle cable out of retainers On machines with loop handle release screws on control handle clamps Take the fixing screw 1 out of the AV sleeve Release the clamp screw 2 Pull out the drive tube On machines with loop handle pull the drive tube 1 out of the control handle 2 at the same time Slip the throttle cable retainer if fitted off the drive tube 12 4 Drive Tube 40 FS 25...

Page 41: ...pairs and Trouble shooting handbook Degrease clamp mounting area Slide the gearhead onto the dri ve tube turn the output shaft back and forth at the same time so that the square end of the dri ve shaft engages the square sok ket in the drive pinion Push the gearhead as far as stop and line it up Tighten down clamp screws to 8 5 Nm Refit the deflector or stop Take rubber element AV system out of cl...

Page 42: ...using Use press arbor 1 1118 893 7200 to remove ball bearing from clutch housing Install in the reverse sequence Use press arbor 1 1118 893 7200 to press home ball bearing as far as stop Use drift 1 1114 893 4700 to press home clutch drum as far as stop 42 FS 25 4 65 4 ...

Page 43: ... Pliers C19 0811 641 8380 Internal retaining ring in clutch housing 13 T handle screwdriver QI T27x150 5910 890 2400 For all IS screws 3 14 Screwdriver T20x100 5910 890 2301 Separating handle moldings 15 Assembly drift 1114 893 4700 Removing and installing clutch drum 16 Vice jaws 5910 893 2700 Holding drive tube and bike handle 17 Press arbor 1118 893 7200 Removing and installing ball bearing in ...

Page 44: ...L special lubricant 0781 417 1315 Bearing bore in rope rotor rewind spring in rope rotor 4 Engine oil SAE 15W 40 Engine lubrication 5 Dirko sealant 0783 830 2120 Crankcase sealing faces 100 g tube 6 STIHL gear lubricant Drive shaft in drive tube 80 g tube 0781 120 1109 225 g tube 0781 120 1118 7 STIHL gear lubricant Gearhead lubrication 80 g tube 0781 120 1117 225 g tube 0781 120 1118 14 2 Servici...

Page 45: ...if faulty if required Engine oil Check oil level x Change x x Complete machine Visual inspection condition leaks x x Clean Control handle Check operation x x Air filter Check x x Clean x x Replace x x Filter in fuel tank Check x x Replace x x Fuel tank Clean x Carburetor Check idle setting cutting tool must not rotate x x Readjust idle x Spark plug Readjust electrode gap x Cylinder fins Clean x Al...

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Stihl FS 25-4, User Manual

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