An Interview With Tim Gilles April 24 2014
Tim Gilles has authored and coauthored several textbooks. He recently retired from the Automotive Technology Department at Santa Barbara City College, after having been a teacher since 1973. He holds a Master of Arts degree in Occupational Education from Chicago State University and a Bachelor of Arts degree in Industrial Arts from California State University, Long Beach. He holds the industry certifications of ASE Master Engine Machinist and ASE Master Automotive Technician.
How did you become aware of the role bolt tension plays in fastener assemblies?
My first exposures to the importance of bolt tension were in my high school automotive and machine shop classes but a good part of my learning about tension and clamping force happened while I was a teacher. The subject became more and more important to me during my 38 years as an engine rebuilding teacher and author. I was always adding new materials to my two lessons on fasteners.
I can't imagine that the prospect of learning about fasteners is going to bring excitement to the average teenager. When they find out that we are going to talk about nuts and bolts I ask them to trust me when I say it's a fascinating subject. They always learn many interesting and valuable things.
What are some common scenarios in which automotive technicians can benefit from using bolt tension testing equipment?
When I was a relatively new automotive teacher at Santa Barbara City College, I invited a guest speaker from Premier Fasteners to come to my class. It was a night class with 25 apprentices who worked during the day in independent repair shops and dealerships. The Premier rep brought along a Skidmore-Wilhelm Model P tension tester and put on a demonstration. He asked for volunteers to come to the front of the classroom and use a socket and breaker bar to tighten bolts of different grades to what they felt was the correct torque. The gauge face was toward the students and the volunteers could not see the increasing tension on the bolt as it stretched. The first two or three volunteers over-tightened their fasteners and the apprentices in the class responded to that with lots of kidding. Naturally, the later volunteers who were more cautious, under-tightened. It was a memorable night for me and a great learning experience for all of them.
A couple of years later when some funding became available, I purchased a Skidmore-Wilhelm Model P tester for the College. I bought lots of Grade 5 and Grade 8 bolts and made it a lab assignment for two students at a time to slowly stretch each grade into yield, see how many degrees it took for them to fail, and finally to break them. Overtightening different grades of fasteners is something every student can do on the tension tester. This has a lasting impact on their knowledge of the importance of correct torque, cleanliness, and the quality of the fastener. They can also understand how torque-to-yield fasteners work.
Sometimes over engineering occurs in structural steel projects because project planners lack confidence in fastener assemblies. Have you seen similar occurrences in the automotive industry?
One thing I can think of in the repair industry is when ARP fasteners are installed in place of rod bolts or main bearing capscrews. When these are tightened to the new, higher torque spec, the assembly goes out of round. The engine builder needs to know that the new fasteners need to be torqued to the new specs and then the assemblies are honed to make them round.
In your opinion are there more issues related to over tightened or under tightened bolts in the automotive industry?
Many bolts were stripped or broken by inexperienced students working on projects in the lab. When I was young, this bothered me. But later I saw this as an opportunity for them to learn to fix their mistakes. As one of my mentors once told me, "older teenagers just need to check everything to see if it's hot". This probably referred more to life than breaking bolts, but I see a parallel.
Not everyone in today's workforce is a professional. There are technicians who have not acquired an appreciation for the importance of clamping force. Some technicians still use impact wrenches for assembly and assume that tight is tight.
What are some common misconceptions in the automotive technician industry related to clamping force and fastener assemblies?
Some do not understand the difference anti-seize lubricants or dirty fasteners make in clamping force, others do not understand fastener grades or problems caused by reusing nuts.
Do you have any best practice suggestions for automotive technicians related to fastener assemblies?
All competent technicians should read a fastener handbook or textbook and learn everything they can. It will prevent comebacks. The 7th edition of my Cengage textbook, Automotive Engines, has a chapter on hardware, fasteners, thread repair and gaskets. There are other textbooks that cover this material competently, as well.
A preview of Tim's book is available below: