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In general, engines can be classified as either interference or non-interference engines. If a timingbelt fails on an interference type engine, the result can be costly damage to related enginecomponents. Many late model vehicles use an interference engine to reduce vehicle weight andunderhood space. Knowing which type of engine is in a particular vehicle can influence the serviceand preventative maintenance schedules.
Illustrated below is what occurs when a timing belt breaks on these different types of engines:
Non-interference engine:
• the engine will run freely with no contactbetween the valves and the piston
Interference engine:
• the engine will not “freewheel”, whichcould lead to severe valve and pistondamage if the timing belt breaks while theengine is running
An asterisk in front of the belt number identifies the
Interference Engines in this application guide.
Example: *TB 191
NON-INTERFERENCE INTERFERENCE
Listed below are general guidelines to follow when replacing a timing belt. Caution: Since all removal and installation procedures vary according tomanufacturer, follow published manufacturers’ recommendedprocedures to ensure proper removal and installation on your vehicle.
• Disconnect the ground cable from the battery.• Remove all drive belts, pulleys, or hoses that could impede removal
and installation.• Turn the crankshaft (in the running direction) to “top dead center”.
Align the marking on the engine case with the markings on thecrankshaft vibration damper and camshaft. (illustration 1)
• Loosen the adjusting screw of the tensioning pulley.• Pull the tensioning pulley away from the timing belt and re-tighten the
tensioning pulley adjusting screw back to its original position.(illustration 2)
• Remove the timing belt (if the belt can not be easily removed by hand, re-check the preceding steps).
• Check tensioner, smooth back idler pulleys, belt sprockets, and othercomponents for wear or damage. If necessary replace them.(illustration 3)
• Properly align all timing marks.• Place the new timing belt on the drive (Caution: never force, twist or
kink the belt while replacing. Bending the belt sharper than thediameter of the smallest system pulley can cause internal corddamage to the belt).
• Loosen the adjusting screw of the tensioning pulley allowing the pulleyto move freely.
• Turn the adjusting screw carefully into its final position (make properallowances for the spring pressure). If the tensioning pulley is notautomatic, tension the timing belt as recommended by themanufacturer using the suggested tensioning gauges and toolsrequired. (illustration 4)
• Re-check the alignment of all timing marks.• Rotate the crankshaft at least two complete revolutions (in the running
direction) to ensure the timing belt is properly installed and tensioned.• Re-check the alignment of all timing marks.• Put the tensioning pulley in its original position and tighten the screws
to the specified torque setting. (illustration 5)
• Replace the timing belt cover as well as any components removedduring the belt replacement procedure.
• Reconnect the ground cable to the battery.• Start the engine.• If any adjustments are necessary, begin anew by disconnecting the
ground cable from the battery.• Dispose of the replaced belt and other components in an environ-
mentally friendly manner.
ill. 1
ill. 2
ill. 3
ill. 4
ill. 5
Changing the belt
Safety Tips
• When installing belts, only use the tools suggested by themanufacturer. The belt must be placed in position manually. Under nocircumstances, should the belt be pried or forced with rim leversscrew drivers, etc. onto the toothed pulleys or rolled onto or overflanged pulleys. Such action will damage the belt. (illustration 6)
• Never allow caustic or corrosive liquids to come into contact with thebelt or drive components. These products can damage the belt and/orplastic parts. (illustration 7)
• Keep the belt well away from oil mist, dripping oil and other chemicals.It is recommended that the belt be kept in its original box until time ofinstallation.
• Always comply with the vehicle manufacturer’s installationinstructions. These are usually printed in the owner’s manual in thesection explaining timing belt maintenance and replacement.
•it in the engine compartment where it can be easily read.
• Replace all defective components, within the timing system, duringthe belt replacement procedure.
• Do not crimp belt or pry onto pulley. Follow shop manual proceduresfor removal and installation.
Storage details
ill. 6
ill. 7
Compliance with storage recommendations will extend the product’s “shelf life” and insure the beltsmaintain their original performance properties.
Please note timing belts should always be left in their original packaging until time of installation. Belts must never be crimped or buckled, as this could damage the integrity and stability of the tensionmembers. Keep belts away from highly flammable, aggressive materials, lubricants or acids.
Fill out the sticker accompanying every timing belt and place
Belts should be stored out of direct sunlight, in a dry location with an ambient temperature of 60-80 F.
Problem and causes Solution
P: Noise from belt while running
1. Tension set too high: belt whines, whistles
2. Tension set too low: belt flaps against the cover or other components
P: Edge Wear
1. Pulleys not properly aligned withone another. Belt runs againstflanged pulley
2. Pulley “cocked” – belt notproperly aligned
3. Flanged pulley is damaged4. Bearing-play in components
resulting in pulley “wobble”
P: Fabric wear on the belt tooth
1. Belt over-tensioned2. Belt is over-heating3. Timing belt sprocket is worn
P: Severe wear on the sides of
the belt teeth, tooth cracking,
or sheared tooth on belt
1. Incorrect tension – too high; too low
2. Trapped foreign matter3. Frozen or jammed timing belt
pulley or tensioning pulley
S: Noise from belt while running
1-2. Adjust tension properly
S: Edge Wear
1-2. Check pulley alignment,replace or adjust parts causingmis-alignment. Replace thebelt
3-4. Replace idler/tensioning pulley.Change the belt
S: Fabric wear on the belt tooth
1. Change the belt and adjusttension properly
2. Determine cause (overtensioning) or heat source. Take corrective action. Changethe belt
3. Replace the timing pelt sprocketand replace the belt
S: Severe wear on the sides of
the belt teeth, tooth cracking,
or sheared tooth on belt
1. Change the belt. Adjust thetension properly
2. Remove foreign matter. Checkfor proper fit of the timing beltcover. Change the belt
3. Determine cause (e.g. defectivebearing) Replace defective partsor component. Change the belt
Problem and causes Solution
P: Grooves or marks on the side
of the belt teeth
1. Foreign matter in the timing beltdrive
2. Scars on the teeth of the timingbelt sprocket caused by foreignmatter or tools used duringinstallation
3. Timing belt damaged before orduring installation
P: Cracks on the back of the
timing belt
1. Ambient temperature too high;too low
2. Contact with foreign matter3. Back idler pulley not operating
properly4. Aging of belt
P: Broken timing belt
1. Foreign matter in the drive2. Belt contact with loose
component or foreign matter3. Excessive tensioning4. Belt was damaged
(e.g. crimped) before or duringinstallation
P: System Components
1. Bearing play2. Damaged running surface
S: Grooves or marks on the side
of the belt teeth
1. Remove the foreign matter.Install new belt. Check to insurethe cover is seated properly
2. Replace the damaged timingbelt sprocket. Change the belt
3. Change the belt using correctprocedures
S: Cracks on the back of the
timing belt
1. Determine cause of abnormaltemperature (e.g. check coldperformance). Repair problem.Replace the belt
2. Change the belt. Check that thebelt cover is seated properly
3. Replace the belt
S: Broken timing belt
1. Remove the foreign matter.Install new belt
2. Determine cause. Eliminateforeign matter. Repair or replaceloose components. Replace thebelt. Check that the belt cover isseated properly
3. Change the belt. Check forproper belt tensioning
4. Change the belt and installproperly
S: Defective System
Components
1. Replace the idler, tensionerand/or guide pulley