Auto Service World
Feature   December 1, 2000   by Jim Anderton

Well belted, Well hosed

Heat and automotive fluids are belt and hose killers

Is belt and hose service too simple to think much about? Maybe, but the combination of relatively easy service and high consumer satisfaction makes it a segment worth chasing, especially with consumer sensitivity to winter breakdowns. For consumers, it’s cheap insurance.

At first glance, belts and hoses would seem to have little in common other than their rubber-based construction and the engine stopping consequences of their failure. Although you can’t easily see it, there’s a great deal of technology in both products, technology which hasn’t changed much in the way technicians handle and install belts and hoses. Knowing what’s there, however, gives technicians and consumers the ability to choose the right product for their application.

Both belts and hoses share a common heritage in that their both composite structures made of rubbers reinforced with strands of fibre molded into the bulk of the material. For belts, the primary force the system must resist is stretching, so reinforcement runs parallel to the loop. Hoses live in a more complex environment because they contain pressurized fluid. That internal pressure attempts to stretch hoses longitudinally, as well as swell them with “hoop stress”. As a result, reinforcement of hoses is often in an angled, “bias” pattern to give the required strength in all directions.

Belt tension is still the biggest issue

Belt tension, or more specifically under tension, is surprisingly common, contrary to the popular belief that modern serpentine belts are essentially trouble-free. According to Goodyear’s Mike Lemkuhl: “In terms of installation, there’s still a lot of v-belts out there. The most common mistake is under tensioning. The biggest issue is the low tension on poly-v (serpentine) belts because people don’t check the tensioner when replacing them.”

Inadequate tension affects belt life both by mechanical damage due to abrasion between slipping belt and pulley, and more importantly by heat buildup due to friction. Add the degrading effects of engine oil, power steering or brake fluid and even coolant, and the result is significantly shortened belt life. One mode of tensioner failure is caused by installation of a belt that’s too short. Operating a belt tensioner too tight takes the pointer outside the allowable marked range, over stressing the tensioner’s internal spring which leads to premature failure. Even if the unit survives, both the belt and engine accessory bearings will wear excessively. The fact is, if the pointer is out of the allowable range, the belt is the wrong size.

Pulley misalignment is also a factor in premature belt failure, and should always be investigated in cases of belt squeal. Belt dressings are at best a temporary fix.

Hoses hurt by oil and heat

Hoses are the other underhood rubber that’s especially vulnerable. Unfortunately, consumers still aren’t accustomed to preventative hose replacement, so in many cases the technician finds out about trouble by way of the green puddle. What makes hoses fail? According to Mike Lemkuhl, “It’s heat. The biggest issue that we have with hoses is that you can’t see them beginning to fail because they fail from the inside out. When the technician’s under the hood, they can’t see the deterioration of a belt, because it’s visible, but a hose fails from the inside, so you don’t see signs of failure until the hose has actually burst.”

The old squeeze test still works, but remember to grip the hose both in the middle and at the ends. External damage and oil-induced swelling are easy to spot, but one failure mode isn’t: electrochemical degradation. Electrochemical degradation is caused by the buildup of electrical charge between hose and metal fittings, and results in tiny longitudinal cracks (striations) near the ends of the hose. The cracks are serious because they allow coolant to eventually contact the fibre reinforcement inside the hose walls, separating the fibres from the bulk rubber. The result is a loss of strength and rigidity that is serious by the time it’s noticeable with the squeeze test. Exhaust manifold heat is another source of reinforcement breakdown, visible as random external cracks. Ozone attack, primarily in urban areas, shows up as crossway cracks. In extreme cases, hoses can be attacked by oil internally, but that’s a situation for more than just a hose change. In each case, however, hose replacement is the only answer.

Can technicians substitute “universal” flex hose for molded hoses? Under a few conditions, the answer is “yes”, but the underhood environment of most cars leaves very little clearance between rotating parts and exhaust components. If an unusual application or emergency forces the use of flex hose, consider the forces acting on the hose during real world driving conditions. Will vibration allow contact with hot or rotating parts? Is the hood pad missing? If so, sharp edges on a hood reinforcement can chafe an upper radiator or heater hose to failure. And finally, consider the forces (especially the longitudinal forces) that will reshape universal flex hoses into a single, constant arc under pressure. The hose will try to “straighten out” if possible when pressurized, and the things that make that shape impossible may include fans, pulleys and belts, or a hot exhaust manifold. Flex hoses can be a risky business, especially since the likely applications will be unusual or rare vehicles. It’s something to think about before you tackle that Bricklin. SSGM

Tensioner Replacement Tips

Gates Canada, supplier of DriveAlign brand tensioners, offers several tips for reliable, damage-free tensioner installation. Take a look at the following, and always refer to the appropriate shop manual for the vehicle:

Mark the rotation direction on the belt

Unload the belt from the tensioner by rotating as indicated by the “rotate to load” arrow

Remove old tensioner

Fit new tensioner

Torque mounting bolts to 1/3 installation torque using a star pattern

Retighten to 2/3 torque then to full torque

Install belt in same rotation as previous

Load belt following the “rotate to load” arrow

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