24 January 2015 | UnderhoodService.com

Technicians and customers havepretty much accepted that the ac-cessory serpentine drive beltshould be replaced between 90,000

to 100,000 miles. It is a “slam dunk” sale tojust replace the belt, but does that replacement

belt have the same chance to survive the samemileage?Chances are in the next 90,000 to 100,000

miles the replacement belt will have to dealwith problems the original belt did not — aworn tensioner, idler pulley bearing failure orcomponent alignment issue. This is why selling the complete serpentinebelt job is important. If just the belt isreplaced, the customer could end up replac-ing the belt sooner than normal and replacingother components when they fail, whichcould leave them stranded.

Belt-On InspectionNoise is the first sign that more components

than the belt need attention. Listen to the beltbefore proceeding with the rest of the inspec-

» Belts By Andrew Markel, editor

The Complete

REPLACING THE BELT IS EASY, MAKING IT LAST IS THE HARD PART

Serpentine Belt Job

» Beltstion. The first clue is a belt squeal heard duringengine startup. The second clue might be a beltsqueal heard during parking maneuvers or dur-ing an alternator load test. While the engine is running, watch the different

runs of the belt and look for flutter or excessivemovement from the automatic tensioner. This canindicate that the tensioner is wornand/or the pulley or decou-pler on thealternatorneeds fur-ther inspec-tion. A spraybottle can beused towet thebelt toisolatetypicalbeltnoisefromtension-er, idlerpulleyandattachedcomponentnoises. Visual inspec-

tion of serpentinebelts is changing.In the past, crackedand missing pieceswere easy to spot. Withbetter materials, cracks andfraying occur less often withinthe 90,000-100,000 mile timeframe. For the major-ity of modern belts, the replacement specificationis the depths of the grooves. When the belt ispast the wear specification, the top of the groovebottoms out on the pulleys. The walls of thegrooves on the belt are no longer able to grip anddrive the accessories. Inspect the outside of the tensioner for rust bleed

seeping from inside the tensioner. This is an indi-cation that the dampener or other internal partshave failed and metal-on-metal wear is happen-

ing. Some tensioners have marks on the housingthat indicate tension and belt stretch, but not thehealth of the tensioner.Look for leaking oil or accumulation of dirt

around the idler and decoupler pulleys. This isan indication the seals and possibly the bearingshave failed.

Belt-Off InspectionPlace a wrench on the ten-sioner and move the armits entire range ofmotion at least threetimes. Feel forspring tensionalong with afluid motionthroughout.Any stickingor notchingmovementmay indicatea problemwith thespring orpivotbearing.The arm

should onlymove up and

down. Any lateral move-ment could indicate a bad bearing

or spring.Spin the pulleys on the tensioner

and idlers. They should spin freelywithout bearing noise, but they should-

n’t spin too freely. A “free-wheeling” bear-ing is a sign that the seals have failed. Any signif-icant amount of noise is an indication that thecomponents are at the end of their life. With the belt off, it is possible to check the

alignment of the pulleys. Belt manufacturers andtool companies offer laser alignment tools foraccessory drive systems that can be very helpfulin eliminating drive belt noise due to misalignedpulleys. These tools typically connect onto a ref-erence pulley like the crankshaft, so the techni-cian can view where the laser pattern falls on thepulleys.

26 January 2015 | UnderhoodService.com

» Belts

28 January 2015 | UnderhoodService.com

It is possible to make adjustments by movingthe pulley on the shaft or adjusting the placementof the components in their brackets. Check theservice information for possible adjustments.

Automatic Belt Tensioner Almost all automatic belt tensioners have a

dampening mechanism that absorbs shocks, beltload changes and crankshaft speed. On someimport applications, the dampener looks just likea miniature shock absorber. On some tensioners,it is a friction dampener inside the housing. Thebottom line is the tensioner mechanism is a wearpart with a limited life span.A worn automatic belt tensioner has conse-

quences beyond a loose belt. When an automaticbelt tensioner wears out, the belt and attachedaccessories will start to take an extra poundingbecause the tensioner can no longer dampen thepower pulses of the crankshaft. The effect onthese components is similar to when a car has

bad shocks that slowly destroy the suspension.A worn tensioner can cause the alternator pulley

or decoupler to work harder and wear out soon-er. The drive accessories can be damaged by theuneven tension and the hammering of the belt.This can damage the bearings inside the alterna-tor and idler pulleys.

Idler PulleysReplacing idler pulleys is cheap insurance

against a comeback. If you miss a bad idler pul-ley, the life of the belt is compromised. Typicallya worn idler will produce a chirping noise. Beltmanufacturers and specialty parts suppliers havekits that include all possible wear items — thebelt, idler pulleys and tensioner. Often these kitsinclude updated parts that can solve belt noiseproblems.

Decouplers and PulleysWhen an alternator decoupler or pulley is com-

30 January 2015 | UnderhoodService.com

prom-ised, it can nolonger absorb thesame level of abuse,which has a trickledowneffect throughout the sys-tem. Belts and tensioners arethen much more likely tooverstress and fail.Alternator decouplers and

pulleys should be inspectedevery 10,000 miles for wear.Early design versions haveprovided service life of40,000 to 60,000 miles, withmore recent versions lastingmore than 100,000 miles. When inspecting a decou-

pler or pulley, there are twosigns that replacement isneeded. First, after shuttingdown the engine, if there isan audible buzzing, thebearings in the pulley havelikely failed. The secondsign depends on whether thevehicle has a one-way clutch(OWC), overrunning alterna-tor pulley (OAP) or decou-pler (OAD).With the inspection

cap/cover removed and the

centerlocked, turnthe pulley ordecoupler with the appropri-ate tool. If it is an OAP orOWC, the pulley can only beturned in the clockwisedirection. If it is an OAD, acounterclockwise turn willreveal a noticeable increasein spring force and a clock-wise turn will only haveslight resistance. If thesefunctions are not opera-tional, the OWC, OAP orOAD needs to be replaced.Anyone can replace the

original belt (most quicklubes are actively sellingbelts), but to make the nextbelt last just as long as theoriginal, there is more workrequired beyond the easysale. �

TechTip: New CarsNew BeltsNew Compounds

Newer engines and enclosed enginecompartments have created an envi-ronment with increased torque de-mands as well as increased underhoodtemperatures. Also, depending uponthe belt drive application, alternatorpulley diameters have decreasedwhich adds to the overall demand ofthe poly rib belt for flexing. In orderto meet and exceed these demands,new belt compounds (EPDM) weredeveloped that provide sufficienttorque capacity these newer enginesrequire, while also performing in high-temperature conditions with improvedflex fatigue characteristics. Belt noise within belt drive systems

also requires a lot of attention. It istrue that because the noise is generat-ed from the interface of the pulley andbelt that the belt is typically blamed forthe cause of the noise. But this is typically not the case. Because of thedemands on today’s serpentine belts aspreviously mentioned, the belt ribshave to be designed to ensure the beltis aggressive enough to pull the re-quired accessory torque load, yet lowenough to allow “quiet” slip duringshift slip conditions and/or slight pulleymisalignments. In most cases, the beltwill perform as expected with no noisegeneration, but if belt noise is experi-enced, the most common causes arepulley misalignment; low belt tension;accessory malfunction/bearing failures;and/or fluid contamination. All of thesepossible causes should be evaluatedand corrected prior to installing a newbelt onto the drive system. daycoproducts.com

» Belts