Streeeetch That Belt

If a customer drives a 2008 Hummer H3 equipped with the LH8 5.3 litre engine into your shop in the coming weeks, you may be at a loss for words if you try to figure out the front of the engine. Effectively, where there use to be a belt tensioner near the air conditioner compressor, you will find … nothing. You will look a second time and when you finally find the belt, you will wonder “How did they figure that one out?”

That GM V8 engine uses a new type of belt that can stretch and it is appropriately called Stretchy (fig. 1). It looks like any conventional belt, but its characteristics are obviously different. It is not built the same way as other belts on the market today and the belt’s wear times and characteristics are different, as well as how the belt is mounted in the vehicle. And it is starting to appear in wide range of vehicles.

For instance, on the GM 5.3 litre, the Stretchy belt drives the air conditioning compressor: it has been used since 2009 in the Chevrolet Silverado -Sierra, Colorado -Canyon, Trailblazer and Yukon -Envoy SUV and the Cadillac CTS-V (compressed).

Chrysler has used the Stretch belt since 2007 in every 2.7 litre V6, appearing in the Chrysler 300, Sebring, Dodge Charger and Magnum to drive the power steering pump. Ford has put it to work for the steering pump on its 3.5 (Flex, Lincoln, Edge, etc) and 3.7 litre V6 engines (Mazda CX-9). It also drives the A/C compressor on the Mazda 3 and Subaru four banger. (fig. 2).

New chemical component

The secret behind this new Stretchy belt is polyamid, one of the numerous forms of polymers used in automotive parts and in tires. It can be compared to the polyester product used in tires. However, polyester does not have the same elastic properties as the polyamid, because of its elasticity, is more suitable to become the base liner of the Stretchy belt. The Stretchy belt is then coated with a new chemical mixture of elastic rubber called EPDM, standing for “Ethylene Propylene Diene Monomer.”

The good news with this EPDM-coated expandable belt is its capacity to maintain the proper tension for as long as 240,000 kilometres when ideal conditions are met. The EPDM rubber coat will resist deterioration and attack from water, chemicals, antifreeze, pollution and oxygen. It will remain flexible within a very large temperature range, from -50C up to 140C. How ever, certification and maintenance of the belt should start around 80,000 km just to avoid any surprises.

But what should a technician do if the belt is removed for whatever reason, say before the 80,000 km? Some manufacturers like GM or Mazda do not recommend giving a second chance to the belt once it has been taken off. On the other hand, Chrysler and Ford say the belt can be reused if there are no problems found with the belt. Dismounting is pretty easy. Ford recommends using a simple tool, a nylon belt. By treading the tool between the stretchy and the ribbed pulley (fig. 3), you only have to turn the crank (fig. 4), and pull towards you (fig. 5) to disengage both. For reinstalling, Chrysler basically recommends using a nylon “tie-wrap.” First, position the belt on the crankshaft pulley -it has holes in it -and solidly fit the tie-wrap around the pulley and the belt at 10 o’clock (fig. 4). Next, place the belt on the other pulley and turn the crankcase clockwise. The Stretchy belt will gradually fit into the grooves of both pulleys. Once the tie-wrap reaches 3 o’clock, you may cut it off: keep turning for a few degrees and the belt will be positioned (fig. 6). Double check the process to make sure the belt is properly mounted on both pulleys. Some manufacturers (Ford, Subaru) will specify a special tool for the job but the tie-wrap will do the job most of the time.

EPDM -Neoprene

Conventional belts made with neoprene need to be inspected starting at around 85,000 km for signs of wear. At this point in the life-cycle of the belt, determining wear is quite simple: tension is inadequate or the belt is cracked, shredded or glazed. Determin ing wear of neoprene belts was a visual affair, (fig. 3) and a typical industry standard was that three cracks within three inches (7.6 cm) would trigger a conventional neoprene belt change.

Finding the wear of an EPDM Stretchy belt is a more complicated affair. The visual characteristic will not be significant enough for many to notice. In fact, the belt might not show any visual wear at all and may run up to 160,000 km and look almost new (fig. 4). A technician may not find any cracks, but the belt will wear thinner, just like a tire does over time and use. After 160,000 km, the thickness of the rib will be reduced by 10 per cent and the belt will be longer than the OE length. At this point, the stretchy belt will loose its tension and could induce slipping. It can even wear down to the polyamid liner, loosing grip on the pulleys, just like in picture 5.

To diagnose an EPDM Stretchy belt, Gates has developed a gauge that will validate the rib thickness (fig. 5). You simply put that gauge between two ribs of the belt and feel the gauge on your fingertip. If you feel the gauge first, maximum wear is not reached and the belt is still good (fig. 6). To make sure, measure all the sipes depth. Once you feel the ribs instead of the gauge, your belt is history.

SSGM