Rotax 655 Troubleshooting FAQ

Copied from the Rotax / Aprilia 655 Engine Manual
Please read the Disclaimer before attempting any work in this FAQ.
20 March 2006

Also check the following FAQs:


The following table(s) and images were recreated from the Rotax / Aprilia 655 Engine manual. The 655 engine is almost the same engine as the Rotax 654 used in the BMW F650 series. One of the biggest differences is the Rotax 655 contains 5 valves, the Rotax 654 engine contains 4 valves. Other than that there are only a few small changes.

Note: Tables are based on carb models
The tables below are based on a carb bike, and not on the newer FI models. However most of it is still relevant for all models.

Engine Related Problems

Engine Difficult Or Impossible To Start

Possible causes Remedy
Spark plug loose Tighten spark plug
Spark plug fouled or wet Clean or exchange spark plug
Spark plug defective Renew spark plug
Spark plug heat range not correct Fit spark plug of specified heat range
No fuel in carburetor Check float level
Valve clearances too small Adjust valve clearances
Valve timing disadjusted Adjust position of camshaft sprockets
Decompressor blocked Check easy movement of decompressor,
Replace pressure spring
Ignition circuit in short-circuit Check ignition circuit, engine-stop-switch and/or side stand safety switch, replace
Electric starter does not spin crankshaft or only by jerks Check battery, replace
Excessive distance between trigger coil and rotor Adjust distance
Ignition coil or ignition cable defective Exchange
Ignition unit defective Check stator, rotor and electronic box,
Exchange defective component
Cylinder head gasket defective Exchange cylinder head gasket
Valves and valve guides worn or imperfect valve seat Exchange valves, valve guides, rework valve seats
Piston rings worn Exchange piston rings
Cylinder bore worn Exchange cylinder

Engine Does Not Function Well At Idle Speed

Possible causes Remedy
Excessive spark plug electrode gap Exchange spark plug
Valve clearance too small Adjust valve clearance
CO-content too low Clean carburetor, check carburetor jets, adjust idling
Decompressor blocked Check easy movement of decompressor, replace pressure spring
Intake flange not tight Tighten intake flange, exchange if necessary
Ignition unit defective Check stator, rotor and electronic box,
Exchange defective component
Valves leaking Rework valve seats

Engine Has No Or Insufficient Performance

Possible causes Remedy
Carburetor soiled Clean jets
Air leak / intake flange not tight Tighten or exchange intake flange
Electrode gap of spark plug too small Exchange spark plug
No valve clearance Adjust valve clearance
Decompressor blocked Check decompressor
Too much oil in engine Drain excessive oil,
Check oil pressure retaining valve
Valve timing disadjusted Check position of camshaft sprockets
Ignition unit defective Check stator, rotor and electronic box,
Exchange defective component
Ignition coil supplies insufficient ignition voltage Exchange ignition coil
Valves leaking Renew valves, rework valve seats
Piston rings worn Exchange piston rings
Cylinder bore worn Exchange cylinder

Engine Is Pinking At Full Load

Possible causes Remedy
Fuel of too low octane number Use fuel of specified octane number
Spark plug of wrong heat range Use spark plug of specified heat range
Air intake system leaking Eliminate leak
Ignition unit defective Check stator, rotor and electronic box,
Exchange defective component

Engine Overheats

Possible causes Remedy
Not enough coolant in cooling system, system leaking Refill coolant, check system under pressure
Not enough oil in the engine Refill oil
Radiator obstructed Clean radiator outside and inside
Thermostat defective Replace thermostat
Water pump or drive gear defective Repair water pump, or check and renew water pump drive
Oil pumps or oil pump drive defective, oil circuit blocked Exchange oil pumps or oil pump gears, clean circuit

Engine Produces Excessive Exhaust Fumes ('Blue Smoke')

Possible causes Remedy
Too much oil in the engine Drain excessive motor oil, check oil pressure retaining valve
Cylinder head gasket defective Replace cylinder head gasket
Valve stem seals worn Renew valve stem seals
Piston rings worn Replace piston rings
Cylinder bore worn Replace cylinder

Engine Vibrates

Possible causes Remedy
Engine fixation has loosened Fasten engine fixation
A bearing or bearing seat is worn Replace bearing or worn component

Oil Pressure Lamp Lights Up

Possible causes Remedy
Not enough oil in engine Refill motor oil
Oil pressure switch defective Replace oil pressure switch
Oil pressure regulating valve blocked or defective
(valve remains open)
Clean or replace oil pressure regulating valve
Oil pump drive defective Replace oil pump drive
Oil pump(s) worn Replace oil pump(s)

Engine Produces Excessive Oil Pressure

Possible causes Remedy
Oil pressure regulating valve defective (valve remains close) Replace oil pressure regulating valve
Oil circuit blocked Clean oil ducts

Engine Operates Excessively Noisy

Possible causes Remedy
Noise seems to come from the valve train
Excessive valve clearance Adjust valve clearance
Decompressor is instable Replace pressure spring of decompressor centrifugal weight
Exhaust camshaft has axial play Adjust axial play of exhast camshaft
Camshaft or bearing supports of camshaft worn Replace camshaft or cylinder head
Camshaft drive is worn or drive sprockets loose Tighten or replace camshaft sprockets
Rocker arm roller or adjustment screw defective Replace parts
Noise seems to come from the camshaft chain
Chain tensioner does not work Replace adjustment spring on chain tensioner, readjust
Camshaft chain or chain guides are worn Replace camshaft chain or chain guides
Noise seems to come from the piston
Piston or cylinder bore worn Replace piston or cylinder
Piston or piston pin worn Replace piston or piston pin
Piston rings broken or ring grooves worn Replace piston rings or complete piston
Noise seems to come from the crankshaft or balance shaft
Bearing of crankshaft or balance shaft worn Exchange bearing of balance shaft or bearing halves of crankcase
or replace balance- or crankshaft
Sprag clutch worn Replace sprag clutch
Axial play of crankshaft or balance shaft excessive Adjust axial play with shims
Split balance drive gear defective Replace springs of split geats, eventually new set of gears
Conrod bearing or crankshaft is worn Replace complete crankshaft
Noise seems to come from the clutch
Friction clutch disks (hammer heads) worn Replace clutch disks
Excessive or insufficient backlash on teeth of primary drive Replace primary drive
Clutch drum, clutch hum or pressure plate is worn Replace worn components
Clutch drum bearings worn Replace bearings or primary drive
Noise seems to come from the gearbox
Tooth flanks of gearbox gears worn Check gears and gear shafts, replace if necessary
Bearings are worn Replace bearings

Transmission Related Problems

Gearshift Function check

  1. Support motorcycle (rear wheel freely turning).
  2. Turn rear wheel and push gearshift lever slowly till stop.
  3. As soon as force is transferred via the selected gear (rear wheel blocking) a clear "click" of index level "2" engaging in the index shim "3" must be heard.
  4. When slowly releasing the gearshift lever, a second "click" (except in 1st and 5th speed) must be heard, caused by re-engagement of the pawl "8" in the pegs "13" of the shaft drum (see "pawl - function check").
  5. If no "click" of the index lever at gear shifting is heard, the engine must be disassembled.

Transmission (Items 1 through 6)

Transmission (Items 7 through 13)

Status for pawl "8"

Gears Jump Out At Start Or At Abrupt Acceleration

Possible causes Remedy
Gearshifting action incomplete Always actuate gearshift lever till stop
Gearshift lever incorrectly adjusted Correct position of gearshift lever
Fastening screw of gearshift lever loose Tighten gearshift lever with specified torque
Gearshift lever bent or touching motorcycle frame or crankcase Replace gearshift lever
(Perform function check as listed above)
Function check with engine removed and disassembled:
Index spring "1" not correctly engaged on index lever "2" Engage index spring
Preload of index spring "1" not sufficient.
Check: The index lever "2" must be able to be lifted only with a certain force "K" from the index shem "3". When turning shaft drum "4" the index spring must press the index lever into the respective "valley" on the index shim "3".
Replace index spring
Index lever "2" is not moving easily.
Check: Check for easy spring movement , with index spring removed.
Replace index lever
Roller "5" of index lever "2" does not slide on index shim "3".
Check: Index lever is bent or rivet "6" of roller is loose.
Replace index lever
Position of index shim "3" in relation to shift drum "4" is incorrect
Check: Check complete engagement of dogs in the gears of the speed selected.

Gear shifting is difficult or jerky

Possible causes Remedy
Gearshift shaft "7" bent or damaged. Return to "neutral" position does not function correctly.
Check: Shift gears, with clutch cover removed.
Disassemble engine and check gearshift shaft with a straightedge (0.3mm deflection admissible). If excessive deflection, replace gearshift shaft.
Function of pawl "8" is not perfect.
(Perform function check as listed above).
Function check with engine removed and disassembled:
Rivet connection "9" of shift lever "10" and pawl "8" not easily movable
Check: Pawl "8" must engage and disengage in pegs "13" when turning shift drum "4". Check for easy movement, with pawl spring "11" removed.
Exchange gearshift shaft with pawl assembly
Hook "11" of pawl spring scours on leg of hairpin spring "12" when shifting up.
Check: Check for sufficient clearance between the ends of pawl spring and hairpin spring
Bend end of pawl spring "11" adequately or replace pawl spring
Pawl "8" scours on shift drum "4" or on index lever "2".
Check: Check for scouring traces and easy movement of pawl. check for correct fit of pawl spring.
Replace pawl spring and/or gearshift shaft complete pawl
Pawl "8" is hooked in one peg "13" of shift drum, with index lever engaged.
Check With index lever engaged, lift pawl "8" from shift drum by hand. If the pawl is hooked in a peg, with index lever engaged in the index shim, check hairpin spring "12" as follows: The two legs of the hairpin spring "12" must be perfectly parallel and lie flat around crankcase boss "14". Only a minimum play between the legs of hairpin spring and rivet "9" on lever "10" is admissible.
Bend ends of hairpin spring "12" until with index lever "2" engaged the status "B" is achieved and pawl "8" can be lift from shift drum without jerks.
Attention: When fitting a new hairpin spring, also make this check, adjust spring by bending, if necessary.
Before engine installation in frame check function and especially "clicking" when index lever "2" and pawl "8" engage!

Gears Can Be Shifted On Warm Engine Only With Increased Force

Possible causes Remedy
Clutch does not disengage Adjust clutch free play of clutch cable correctly
Clutch does not disengage. Due to expeansion and wear of the clutch cable the clutch freeplay is excessive.
Check: Check both ends of clutch cable for perfect condition
Renew clutch cable
Clutch does not disengage - wrong position of clutch release lever Fit clutch release lever correctly.
Clutch does not disengage - clutch release lever not tightened enough Fit clutch release lever correctly and fasten tightening screw at the specified torque
Clutch does not disengage exactly - clutch disks excessively warped Check warping with straightedge, replace clutch disks if necessary
Clutch does not disengage - clutch release lever defective or cracked Replace clutch release lever
Clutch does not disengage exactly
Check: The outer offset disk should only have a minimum of freeplay, however not squeeze in clutch drum.
Change the outer friction clutch disk against an other friction disk of the disk package which does not squeeze
Gearshift shaft bent.
Check: Only possible on engine disassembled - see above checking and remedy hints
Replace gearshift shaft and check gear shifting

Gears Can Be Shifted Only Noisily

Possible causes Remedy
Final drive chain tension too loose - whip effect when shifting gears up and down Tension final drive chain as indicated and check clutch adjustment
Clutch does not disengage See hints above regarding "Clutch does not disengage"

Clutch Slips

Possible causes Remedy
Insufficient clutch freeplay Adjust clutch freeplay
Fatigue of clutch springs Replace clutch springs
Friction clutch disks worn Exchange friction clutch disks
Engine oil with "Friction Modifiers" Exchange engine oil, wait for further 500 kms

Clutch disengages unsatisfactorily

Possible causes Remedy
Engine oil of wrong oil specification used Use engine oil specified

Clutch "Drags" at Engagement

Possible causes Remedy
Friction and steal clutch disks warped or warn Renew disks
Guide slots for clutch disks in clutch drum are worn Replace complete primary drive
Guide slots for the steel disks in clutch hub are worn Replace clutch hub

Ignition Unit Problems

The ignition unit is a breakerless capacitor discharge unit with electronically variable ignition timing and a 3-phase AC generator (12V 280W). It cannot be adjusted and is maintenance free. [Ed note: The AC generator was increased to 400W on later models].

Never disconnect electrical connections while the engine is running

Before any repair, remove ignition key and disconnect battery (first minus pole). Caution: high voltage on ignition unit!

Attention: The amplifier box must not be exposed to mechanical impacts. For removal of rotor use puller (976 235) and protection mushroom (277 135).

Ignition Unit - Components

  1. Stator
  2. Magneto flywheel
  3. External trigger
  4. Electronic box
  5. Ignition Coil
  6. Spark plug connector
  7. Sprag clutch
  8. Electric starter
  9. Ignition cover

Ignition Unit - Wiring Diagram

  1. Generator
  2. External trigger
  3. Electronic box
  4. Battery
  5. Ignition switch
  6. Emergency switch
  7. Side stand switch
  8. Spark plug connector
  9. Spark plug
GWGreen - white stripe
LWBlue - yellow stripe

Ignition Unit - Troubleshooting

If the ignition unit does not supply an ignition spark or if it is suspected there may be an ignition problem, check the following parts in the sequence indicated, or determine the function by exchange of parts:

Note: Before checking, disconnect plug connections. Measure the resistance between 2 measuring points (cables), adjusting the instrument to the required measuring range and adjust the Zero point.

  Measuring pointsResistance
(at 20C)
AC generator Coil exitY - Y0.2 - 0.5 ohms
SensorGW - LW190 - 300 ohms
Ignition coil Primary windingterminal - core0.2 - 0.5 ohms
Secondary windinghigh tension wire - core6 - 13 k ohms
Spark plug connector Connection for ignition cable -
Connection for spark plug
0.8 - 1.4 k ohms

Electronic Box - Check

Note: For checking of electronic box set measuring range of 1k ohm to 10k ohm on the instrument. Also at each measurment take care of the polarity of the cables of the instrument. If one or several values do not correspond with the values indicated, the defective part of the ignition unit must be replaced.

Electronic Box
ND 071000-0790
- instrument cable (black)
G ooooo
Wo oooo
Ox> >xx
Rooo oo
Boooo o

o = passage (instrument dial moves, measuring value of no importance)
x = no passage (instrument dial does not move)
> = instrument dial may move than returns to infinate