SKF Timing Belt Kits - SKF.com

Engine drive systems
Technology and material changes
Many components and systems in the engine depend
on the correct functioning of the timing and auxiliary
drives. This is also driving the technology and design
of these systems, so they can live up to the more
demanding criteria required.
Timing drive system
The controlled operation of this system is dependant
on either a chain or a belt. A general drive for design
improvement for performance gain, coupled with the
pressure to reduce emissions, have seen twin overhead
cam, multi-valve engines become commonplace.
Timing belt
A timing belt is typically rubber with high-tensile fibers
(e.g. fiberglass or Kevlar) running the length of the
belt. Rubber degrades with higher temperatures and
contact with motor oil and antifreeze. Therefore, the life
expectancy of a timing belt is lowered in hot or leaky
engines. While older belts were of chlorobutadiene
rubber material and trapezoidal shape, today’s modern
belts are even more specific to particular engine
designs, with subtle profile changes to the curvature
of the teeth. In addition the improved material means
these new designs optimize the power transfer without
wear or noise, reaching ever higher lifespans in excess of
over 93,000 mi/150 000 km.
Timing chains
Encased on the front of the engine, this power
transmission drive frees up space to give the auxiliary
system more space. On average, these chain systems
have a longer life span on recent engines. The typical
life of a chain is around 74,500 – 155,300 mi/120 000
km – 250 000 km. The disadvantage with chains is that
they are noisy in comparison with belts and they lack
the capacity to handle modern hp injection systems.
In the immediate future (5–10 years), new cars sold
with chains fitted on the engine drive system will rise by
around 50%.
Timing system, belts vs. chains
For car manufacturers, engine assembly is all about
numbers built – faster. Unfortunately, the time taken
for the ABTU and belt on the timing system to be set up
correctly, can eat into production time. Chains are easier
and faster to install. This fact contributes to the use of
chains today. The use of high performance material such
as HSN, advanced automatic tensioner units, specialized
bearings and pre-set tensioner springs for speedier and
easier mounting, adds up to belt systems that reach
the life time level of chains, while still offering design
flexibility, cost and weight savings, as well as easier
maintenance in the aftermarket. This is an advantage
when it comes to car manufacturers’ choice. But, for
now, chains are still the preferred option.
Timing belt system
Timing chain system
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