BELT
DRIVE ALIGNMENT AND TENSION
By James Pfeifer
For those of you who have
purchased or plan to purchase a belt drive system, you have made an intelligent
choice. When properly applied and maintained, belt drives are proven to
be cleaner, quieter and more efficient than chain drives. To maximize the
performance and life of your belt however, close attention must be paid
to the alignment and tensioning.
Maximum drive performance
and belt life are achieved when the belt is properly tensioned and maintained.
Place belts on pulleys and adjust the take-up so that the belt teeth mesh
securely with the pulley grooves. Check the tension using a belt tension
gauge. While over-tensioning the belt can impose higher bearing and shaft
loads and lead to reduced belt life, under-tensioning results in the belt
being too loose. When the belt is too loose for the load, the teeth climb
out of the pulley grooves, leading to increased stress on the belt teeth,
accelerated tooth wear and reduced belt life.
When the belt is severely
under-tensioned, belt ratcheting (jumping teeth) occurs. At that point,
significant shaft separation forces are developed in the drive, resulting
in damage to bearings, shafts and other drive components and the belt.
You use an air pressure gauge to set up your tires and a degree wheel and
dial indicator to set up engines; why not set belt tension the proper way?
Use a belt tension gauge.
Misalignment is another
problem that can result in reduced belt life. Belts are sensitive to misalignment,
and should not be used on drives where it is inherent to the drive operation.
Misalignment leads to inconsistent belt wear and premature tensile failure
due to unequal tensile member loading. In a belt drive that is misaligned,
the load is being carried by only a small portion of the belt top width,
resulting in reduced performance.
There are two types of
misalignment: parallel and angular. Parallel misalignment is where the
shafts are parallel but the two pulleys lie in different planes. When the
two shafts are not parallel, the drive is angularly misaligned.
Any degree of pulley misalignment
will result in some reduction of belt life. Misalignment should be checked
with a good straightedge tool. Make sure that the shaft of the engine is
parallel with the rear axle, and that the rear axle is perpendicular (90
degrees) with the center of the crankshaft.
About the author: James
Pfeifer is the president of Pfeifer Industries, West Chicago, Illinois.
Pfeifer Industries is the leading belt drive system manufacturer for karting.
WHAT IS THE SFI FOUNDATION?
What is the SFI Foundation,
Inc.?
The California-based
SFI Foundation, Inc. (SFI) is a non-profit organization established to
issue and administer standards for specialty/performance automotive and
racing equipment.
Who uses SFI Standards?
Manufacturers of equipment
are the primary users of SFI standards. Some standards are adopted as part
of the rules of race sanctioning organizations. Ultimately, the consumer
benefits from the program as it establishes recognized levels of performance
or quality for a product.
How is the SFI standard
program funded?
Participating manufacturers
pay for development and administration of these programs through licensing
fees and or unit charges. Also interested associations have provided grants
and donations.
How is a standard initiated?
The SFI Technical Committee
initiates the specification process, typically at the request of the affected
industry or race sanctioning body.
What about enforcement?
Typically, there are
policing provisions through contractual or licensing agreements whereby
SFI may inspect the records and/or equipment of a manufacturer in order
to ascertain that the product involved meets SFI specs. Once a manufacturer
has voluntarily committed to participating in the program, he must comply
with the specifications in all respects.
How are specs used in
racing?
When adopted as part
of the rules of a sanctioning body, enforcement is entirely up to that
organization. The manufacturer then provides the racer with product which
is in compliance with the specs enforced by the sanctioning body.
SFI SPEC PROGRAM – Administrative
Procedures
Purposes
SFI Specs Programs are
intended to serve the following purposes
a. To promote quality
and reliability in the design, manufacture and application of products
of the specialty parts industry.
b. To provide seller
and purchasers information to facilitate purchasing and application decisions
c. To provide officials
of competition events with convenient and reliable references for evaluating
products.
Openness
Participation shall be
open to all interested persons who might be directly or materially affected
by the Specs. Participation is not conditional upon membership in any orgainzation.
Technical Committees
Technical committees
are comprised of individuals from all facets of industry, scientific and
motorsports sanctioning organizations with expertise in their areas of
endeavor to provide a comprehensive cross-section of knowledge.
Due Process
Open hearings with adequate
notice of all activities shall be given, copies of these procedures shall
be available, and the opportunity to be heard or to appeal any decision
shall be provided to all interested parties. All activities are to be conducted
with fairness toward all interested persons.
Publication and Disclosure
SFI Specs shall be published
and made available to the public as soon as possible after approval by
the SFI Board of Directors.
General
SFI is responsible to
monitor adherence to the Specs Program by verification of certified test
reports from recognized test laboratories and performance audits where
applicable as defined by the Spec procedures. Each SFI Spec will be reviewed
periodically by committee members, to revise and update as required by
current technology.
SFI LABORATORY SERVICE
Lab Purpose
SFI has recognized the
need for a totally dedicated and equipped laboratory to service the needs
of its participating manufacturers. Manufacturers deserve a completely
focused, professional facility to process their testing requirements. With
that mandate in mind, SFI has developed a comprehensive in-house facility
capable of meeting the needs of affiliated companies. It is their mission
to provide consistent and reliable test results in a timely manner and
at reasonable costs. At the same time, the SFI facility is available for
prototype (non-certified) and non-SFI testing to other specifications.
Testing for Certification
This testing is required
by the pertinent SFI specification and will provide a certified report
of compliance to that SFI test requirement for either initial validation
or certification renewal.
Prototype Testing
The availability of the
SFI lab for consumer product development and analysis will provide an opportunity
for confidential research as it’s related to SFI specifications. As this
testing is not done to demonstrate compliance, no certification will be
provided with the test results, SFI will therefore be able to offer this
capability at a reduced fee from it certification testing.
Audit Testing
Many of the SFI specifications
grant SFI the right to purchase product on a commercial basis and subsequently
test that product for compliance to that spec. SFI will conduct these audits
on a random basis but with the understanding that such tests will also
serve as the re-validation testing required by the pertinent spec.
Testing To Non-SFI Standards
Although the laboratory’s
main function is to service SFI manufacturers, the facility is available
to anyone wishing to perform testing to other specifications, i.e., ASTM,
NFPA, FAA, SAE, etc. This can be product development, R&D or an ongoing
quality control program.
Types of Testing Available
at the SFI Lab
Mechanical Properties:
Tensile, Elongation, Yield
Rotational Integrity (Spin
Test)
Thermal Protective Performance
Flammability
Thread Heat Resistance
Zipper Heat Resistance
Thermal Shrinkage Resistance
Explosion Containment
Absorption Capability
Seat Belt Breaking Strength
Lug Nut Tests: Thread
Quality, Tensile, Galling, Chrome Plating Evaluation
Window Net Tests: Penetration
Resistance, Rapid Impact Resistance (Drop Test)
For more information contact:
SFI Foundation, Inc., 15708 Pomerado Road – Suite N208, Poway, CA 92064.
Telephone: 858-451-8868, Fax: 858-451-9268. Web site: www.sfifoundation.com.
END
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