troubleshooting and repair

8/11/2019 Troubleshooting and Repair

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4-MIX Troubleshooting and Repair

Before any repair work is performed on a machine, a thorough evaluation sho uld be madeto d etermine what parts are actually in need of r eplacement or maintenance. The servicemanuals for STIHL 4-MIX engines outline testing pro cedures as well as special tools th atare needed to repair the equipment.

The STIHL troubleshootin g video and c orrespondin g iCademy module are ideal checkliststo use when performing repairs and will assist the technician in performin g a step by stepanalysis of th e machine.

Repair Procedures: Quick Check

The fastest way to find any major fault is to quickly check for co mpression, ignitio n, spark,and fuel delivery.

Use a spark tester to verify th at spark is present. If the engine has no spark, the spark plug, the ignition module or sto p switch

system is at fault. If the fuel system is co mpletely restricted, the engine may not fire at all when tryingto start it. Squirt some chok e spray in the carburetor and try to st art the engine.

Does the engine have anycompression?

Is fuel getting to thecombustion chamber?

Does the engine havespark?

On 4-MIX engines , if compression feels low, or if the spark is ok ay and fuel is getting tothe engine, then do a leak down test.

This only takes a few minutes. If the leak down is below 10%, then the combu stionchamber is okay and the running problems are due to something else.

If the leak down i s greater than 10%, the pro blem needs to be repaired, as well asmaking su re that there are no other faults present.

If leak down i s less than 10%on a 4-MIX engine, check forfaults elsewhere.

If leak down is gr eater than 10%, theengine will need service, but check forany other faults before doing anyrepair.


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Click to download the STIHL 4-MIX Engine Check Worksheet .

The STIHL 4-MIX Engine Check Works heet is a simple guid e to verify any fault sfound in a logic al and efficient manner.

Worksheets are available for both 2-cycle and 4-MIX engines . An accurate repair cos t es timate can then be prepared.

Throttle Operation

Verify that the thrott le works smoo thly, and that the throttle interlock is working correctly.

The throttle cable should b e adjusted so that the throttle is opening all the way tothe stop on the carburetor without c ausing excessive tension on the cable.Example A.

Be sure that the throttle returns to idle easily and smoothly. On a shaft mounted 4-MIX produc t, inspect the cable for fraying where it slides

over the plastic cam on t he carburetor flange. Example B.

B

A

4180 Series Throttle Adjustment Procedure

To adjust the throttle correctly on a shaft mounted produ ct, set the screw on theadjuster cam that is loc ated on the carburetor flange so th e same amount o fthreads show o n either side of th e cam.

Next, using a small screwdriver, push dow n on the tab located in the top of thethrottle assembly and sli de the tab towards the engine.

Now squeeze the throttle to th e wide open position . The tab will sli de forward andautomatically adjust th e throttle cable. Release the throttle trigger and v erify thatthe throttle lever comes back fully to i dle.
http://www.stihlicademy.w1.com/reference08/4-MIX_Engine_Check.pdfhttp://www.stihlicademy.w1.com/reference08/4-MIX_Engine_Check.pdf


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The throttle cable should always be checked for pr oper adjustment when a new machine isset up for delivery and anytime a machine is in for service.

4282 Series Throt tle Cable Adjustment

If the throttle is no t opening all the way on a backpack blow er, performance andengine cooling will su ffer.

To adjust the throttle cable on a 4-MIX blower, turn the small screw that is locatedin the throttle trig ger until the prop er throttle opening is achieved.

Ignition Module

Check for s park with a spark tester that loads the ignition mo dule.

Modules can have intermittent faults: Heat related failures wh ere the spark returnsafter the module cools down , or even show spark but no t start the engine.

Check for s park. The spark plug mus t be installed in the cylinder when performingan ignition module test with the STIHL ZAT 4.

Holding the plug against the cylinder and pulling t he starter rope is not a valid testof an ignition mod ule.

Inspect the spark pl ug and verify heat range.

Verify that th e correct spark plu g is in stalled. The spark plug for an FS 100 is hotterthan the spark plug for a BR 600.


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If an incorrect spark p lug is installed in a BR 600, the engine may quit after it warmsup, or it may run poorly. It may also try to ru n-on when the ignition is switch ed off.

Set the gap on all STIHL spark p lugs at twenty th ousands o f an inch. The final verification of a faulty igniti on modu le may have to be done by replacing it

with a known good ignition module for comparison.

FS 90, FS 100, FS 110,KM 110, FC 100, FC 110,HT 100, HT 101 , HL 100

FS 130, KM 130,HT 130, HT 131BR 500, BR 550, BR 600

STIHL 0000 400 7009Bosch USR7ACNGK CMR5H

STIHL 0000 400 7011NGK CMR6H

Refer to the STIHL repair s pecification ch arts for other mo dels.

Air Fi lters

Air fil ter s should be inspected and cleaned regular ly . Filt ers shou ld be replaced at leastonce a year, or more often if needed.

The air filter element used on the 4-MIX shaft mounted engines shou ld never becleaned in sol vent. Brush off any loose debris and clean it with c ompressed air.

STIHL backpack blower engines use a pleated paper air filter. The only way toservice it is to brush of f any debris or gently blow it off. Do not use high pressureair or th e pleats may tear.

Alw ays inspect the clean s ide of the fi lter housing fo r any evidence of dirt or gr it . Ifdirt is present, the filter needs to be serviced more often.

Flywheel

Fault A sheared flywh eel key.

Occurs when: The nut is not pr operly tightened, or if an impact wrench is us ed toloosen or tighten the fan wheel, flywheel, clutch, or s tarter cup nut.

A sheared key may not cause the ign it ion module to lose spark, so the spark testerwill not show a fault.

Ke i s sh ear ed.

Never use animpact wrenchon any STIHLproduct!

Verify flywheel timing.


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The shaft mou nted 4-MIX engines have a timing arrow o n the flywheel that shouldpoint at the ignition mo dule mounting sc rew as a reference point when the pistonis at top dead center.

For the 4-MIX blower engine the S marked corner on the flywheel should be justat the edge of the ignition armature leg when the pis ton is at top dead center.

Shaft Mounted Engine

Ignition Module Air Gap.

The specification for th e ignition modu le to flywheel air gap is eight thousandths o f

an inch for all 4-MIX engines . The STIHL setting g auge can be used to check and p roperly adjust the air gap.STIHL Part # 4118 890 6401.

Backpack Blower Engine

Backpack Blowers4282 Series

Shafted Product s4180 Series

Valve Clearance

Break-in and nor mal wear tend to op en up th e valve clearance, and may l ead to a loss ofpower and performance.

The valve clearance for all 4-MIX engines is 0.1 mm. or four tho usandths of an inchwhen the engine is cold .

The instruction manual suggests checkin g the valve clearance around 135 hours ofoperation.

A cylinder pressure leak down tes t wil l allow you to qu ickly determine the condi tionof the valves and piston rin gs witho ut disassembling the engine.

A special feeler gauge is required to check the minimum valve clearance. STIHL Part# 4180 893 6400.


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Check valveadjustments

Leakage % isindicated on gaugethat is connectedto cylinder.

Adj us t reg ul atorgauge to the set-point.

Engine - Leak Down Test

Test the 4-MIX engine for leaks.

Connect the gauge to th e engine and read the amount of leakage.

There may be a litt le leakage past the end-gaps of t he rings. If leakage isless than 10% the sealing of th e combusti on ch amber is acceptable.If leakage is over 10% you will need to identify the area of leakage and repair theleak.

Listen at the muffler, carburetor, flange inlet, or where the push rods c ome up fro mthe cam. A rushing air sound should be evident at one of these locations, verifyingthe location of th e leakage from th e engine.

The leak down tester recommended by STIHL has a smaller air inlet ori fice and is designedfor testing any small engine.

Crankcase - Vacuum & Pressu re Test


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Install the rubber block off pl ate between the muffler gasket and the engine andinstall a flange adapter in p lace of the carburetor. Be sure to block the impulsehose.

When checking th e crankcase for leaks, pressurize the crankcase to a reading ofpositive 0.5 bar, or about 7 poun ds per sq uare inch. The pressure should not leakdown t o posi tive 0.3 bar, or about 4 pounds per square inch, in 20 seconds. If it willnot ho ld pressur e or leaks down to o fast, locate the leak with a soapy watersolution.

To perform a crankcase pressure and vacuum test the intake port and exhaust port mu stbe sealed with the proper bloc king too ls. STIHL 4-MIX engines need to also h ave thevalve cover ins talled.

Gauge readings.

If the crankcase holds pressure, then apply a vacuum of negative 0.5 bar, or aboutnegative 7 pound s per squ are inch. The vacuum reading shou ld not leak to abovenegative 0.3 bar, or about negative 4 pounds per square inch, in 20 seconds.

If the engine has a vacuum l eak, but no pressure leak, the fault is mos t likely acrankshaft seal. Expose each seal and positio n the engin e with th e seal facing up,spray some light p enetrating lub ricant on th e seal around the crankshaft and applya vacuum with the tester to see if any of the liqu id is su cked into th e seal.

VacuumRange

PressureRange

Impulse Line Check impu lse line for block age.

One method to check the impu lse is to use a small carburetor pressure tester, andhook it to th e impulse hose.

When you pull the starter rope, the needle on the gauge should bounce back andforth in dicating pos itive and negative pressure. If nothi ng happens, the impulseline or imp ulse passageway is restric ted.


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If the starter is not assembled to the engine you can connect a carburetor testinggauge to the impulse hose when you p erform a crankcase pressure and vacuumtest.

The needle on the carburetor gauge should move as pressure and vacuum areapplied to the crankcase.

If the impulse line becomes blocked, the running behavior of the engine will indi catecarburetor prob lems, when in fact there may be none.

Carburetors

Inspect carburetor visually.

Before testing or di sassembly, visually inspect th e carburetor for damage.If something on the carburetor is physically bro ken or worn, most likely thecarburetor will n eed replacing and n o further tim e will be spent on evaluation.

If the carburetor has no ph ysical damage and the thrott le shaft is tight, then perform

a three step evaluation with a carbureto r press ure tester, suc h as a ZAMA ZPG-1.This will allow any internal faults in the carburetor to be identified quic kly.

Fuel Leak Indicated byDirt Build-up

Worn Throttle Shaft

Worn Mounting Surface

Three step evaluation for a 4-MIX engine used on shafted products.


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Acc elerat orPump Bore

LiquidDrawn In

Fuel Tank

Test fuel t ank and tank vent.

It is a good practice to always pressure test an empty tank

to be sure it has no leaks. Then perform a vacuum test toverify that the tank vent is allowing air into t he tank. A poorly vent ing t ank can cause running behavior such as

engine stalling when hot, poor acceleration, or loss of pow erwhen hot.

Special Service Procedures

Special Tool Application: 10mm Piston Stop, Flywheel Removal.

To remove the flywheel or s tarter cup nut on a 4-MIX engine , block the piston wit hthe p isto n s top . STIHL Part # 4282 890 2700.

Install the flywheel puller, part number 1116 893 0800, until it seats against theflywheel, then back it off on e full turn . Hit it s quarely with a ball peen hammer to

release the flywh eel fro m th e crankshaft. Do not use an impact wr ench on any STIHL product.


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Remove Fan Wheel: BR 500, BR 550, BR 600.

To remove the fan wheel on a 4-MIX backpack blower, block the piston with thepiston stop and u se a inch breaker bar with a 17 mm. socket to u nscrew the fanwheel. Piston stop STIHL Part # 4282 890 2700.

The mounting nut is molded into t he fan wheel as one piece and has right h andthreads.

It will be extremely tight, and may take one person to hold the engine and fanhousin g while another applies pressure to the breaker bar.

Do not use an impact wr ench on any STIHL product.

Engine De-Carbonizing Procedure.

If a 4-MIX engine is showing more than 10% leakage past the exhaust valve, themost lik ely cause is carbon build-up on the valve face.

STIHL Engine Decarbonizing liquid can be used to soften and flush o ut carbondeposits. Engine treatment involves pu tting th e piston at top dead center on valveoverlap, where both valves are slightly open at the same time. This is 360 ofcrankshaft rotation fro m top dead center on the compression stroke. With thevalve cover removed this is easy to verify.

Then fill the cylin der with the decarbonizing liquid .

STIHL 4-MIX Cam Timing: Back pack Blowers 4282 Series


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If the engine is being assembled and the flywheel is not in place yet, just be sure thepiston is at top dead center to time the cam correctly.

To install the cam on the backpack blower engines, notice that when the piston is attop dead center, the cam lobe is pointin g up w hen the alignment marks arematched up. Now install the dowel pin.

Rotate the crankshaft until the tip (arrow) of theflywheel lines up with the ignition module asshown.

Fit the cam gear so that the arrows (2) and (3) arein alignment w ith the notc hes (1and 4) in thecylinder.

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