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Engine Timing

OAP Technology and Quality

INA, inventor of the overrunning alternator pulley (OAP) warns factors and garages to beware of cheap imports and explains why it is worth investing in OE.

The power and compression strokes of the internal combustion engine involve the acceleration and deceleration of the crankshaft whose rotational irregularities are transferred to the engine accessories through the accessory drive belt. This eventually causes issues such as: increased noise and vibration levels, excessive force through the tensioner and belt, and ultimately the premature wear of components in the drive system.

The alternator has the biggest impact on the accessory drive belt. To help protect all of the ancillary components driven by the belt, INA’s engineering team developed the overrunning alternator pulley (OAP), which allows the alternator to decouple from the drive system and prevent premature wear. Engine designers were quick to spot the potential of the idea, and since 1995 INA has provided more than 60 million OAPs to vehicle manufacturers worldwide.

In fact, the OAP is so successful that competitors are producing their own ranges by attempting to copy the original INA design and technology. So, when a new product appears on the market, INA product engineers test it against OE specifications. The objective is to measure torque and coupling durability, bearing fatigue and the overrunning function whilst also giving a direct comparison to the INA original equipment unit.

Extra Protection

Another feature of an INA OAP is that even in the unlikely event of component failure it will continue to maintain its full running properties because it has been engineered to fail in a ‘locked’ position. This element of the design allows the auxiliary belt to continue driving the alternator even if the internal mechanism of the OAP has failed, and is unique to INA products. Every competitor design tested so far has failed to include these emergency running properties, so there will be no drive to the alternator when it fails.

Some manufacturers are now issuing “5 Year Life” testing certificates (guarantees the part will have a 5 year life) with their products, but fail to mention that the testing involved is purely an operational function test and is not carried out to the same specifications and guidelines which are placed upon INA as an original equipment supplier. This could mean that there will have been no speed and load variations imposed on the components during the test, which will no doubt fall well short of the 1,000 hours expected to be completed if the part is intended for fitment as original equipment.

Schaeffler OAP Comparison Results

Each OAP was tested for up to 600 hours on a heated mounting at a radial load of 1,000N and at speeds of up to 6,000rpm, with half the time loaded and the other half unloaded to best simulate engine bay conditions.  

The test results show that the two competitor OAP units failed well short of the 600 hour target, whilst the original INA components all sailed through the test, easily exceeding the lifetime expectations of the part. The INA units also achieved a maximum alternator speed of 20,000rpm (whilst still retaining full drive capacity) as well as a maximum engine speed of between 6,666 and 8,000rpm, depending on the ratio. The competitor units started to slip (losing drive) at a speed of around 8,000rpm, with a maximum engine speed of 3 – 3,600rpm. These results highlight the inability of the copied components to reproduce the decoupling effects of the original equipment part without incorporating the advanced technology that is built into each INA unit.

To guarantee that your replacement OAP is not going to let you or your customers down, insist on supplying a genuine INA part – designed and engineered by the ORIGINAL manufacturer. With an aftermarket range of 160+ part numbers, INA is the global market leader in OAP technology.

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