Rod ends are one of the most neglected items on your vehicle, be it a race car or street car, yet they are one of the most important in terms of safe operation. It is safe to say, “You get what you pay for and you pay for what you get,” when it comes to rod ends.
At FK Rod Ends, we don’t buy offshore rod ends and put them in a box. We design, engineer, test, and make rod ends in the USA. - Jeff Stacy
Stacy walked us through the importance of rod end maintenance, and taught us the differences in type and quality of rod ends.
Routine replacement of rod ends is part of good maintenance practices on any racecar. “My advice is to inspect them frequently and replace them often,” said Stacy. “A rod end failure can be catastrophic to the racecar, so $400 worth of rod ends is cheap insurance.”
What Is A Rod End?
A rod end is simply a mechanical articulating joint that is commonly used on the end of control rods in aircraft, boats, and automobiles. The rod end has a ball bearing type swivel that has an opening through which a bolt or stud passes through. The ball bearing swivel is pressed into a casing that has a threaded shaft incorporated into it. The threaded shaft can be male or female, and is used to attach the assembly to a threaded control rod.
About FK Rod Ends
FK Rod Ends is a leading manufacturer of rod ends and spherical bearings for the industrial and automotive industries. Headquartered in Southington, Connecticut, FK Rod Ends is a family owned and operated business that has specialized in quality products for over 25 years.
The company prides itself on supplying the automotive industry with high quality products, fair pricing, and quick delivery. FK Rod Ends and their sister company, Fragola Performance Systems, pride themselves on rapid order fulfillment times, and the ability to react quickly and fulfill a customer’s immediate request without a manufacturing delay.
Originally starting with rod ends and spherical bearings made from mild steel, the FK line of products has grown to almost 10,000 combinations of rod ends and spherical bearings available. From mild-steel to chromoly, alloy steel, aluminum and stainless steel, there is the right rod end for any industrial or automotive need - and it’s probably stocked and on the shelf awaiting the next order!
The History of Rod Ends
The spherical rod end bearing was developed by Messerschmitt AG German aircraft manufacturing company for use on aircraft in World War II. One of the first German planes, a Messerschmitt that was shot down by the British in early 1940, was examined thoroughly. The allied forces found this strange joint in use in the aircraft’s control systems.
In an effort to conserve valuable resources for the war effort, the H.G. Heim Company in the United States was awarded the exclusive patent to manufacture the new joints in North America and the Rose Bearing Ltd company in the United Kingdom. These joints became known by their exclusive manufacturers and many times are still referred to as “Heim joints” in the U.S. despite being made by another manufacturer.
Once used strictly in aircraft, these spherical joints are found in just about every type of vehicle on air, land, sea and space today.
Just by glancing at a rod end, it’s almost impossible to know what a quality rod end bearing looks like, however, selecting a quality rod end isn’t as difficult as it may sound. According to Stacy, “An American-made rod end manufactured out of certified material is the only true method of rating a rod end as a quality rod end.” FK Rod Ends stamps “USA” in the housing of every rod end to let their customers know that the rod ends are manufactured right here in the USA under tight manufacturing tolerances.
“We don’t buy offshore rod ends and put them in a box. We design, engineer, test, and make rod ends in the USA,” Stacy assured us. “That means something to us.”
Examining rod ends like you would any other piece of hardware is instrumental in selecting the best bearings for your application. Take a good look at the machining of the rod ends. Check the bearing race and examine the actual bearing itself. These should all be machined well and smooth.
Check the threads on the rod end shank. Rod end shanks can be external or internal threaded shanks. Quality rod ends that have external threads will have rolled threads, like quality fasteners do. It is widely accepted that rolled threads are stronger than cut threads, having as much as a 20-percent increase in tensile strength over cut threads.
The spherical ball should fit tight inside the body and move precisely. Always check rod ends by rotating the ball to ensure that there are no binds and the ball isn’t so loose that it rattles. If there is a teflon liner, look for areas where the liner is loose and the bonding has failed.
Two-Piece or Three-Piece Construction
When discussing types of rod ends, there are two basic categories. Speaking strictly from the construction of the rod ends, it comes down to either two-piece or three-piece construction. “A two-piece construction is where the spherical ball is pressed into the housing,” explained Stacy. “A three-piece constructed rod end has the spherical ball pressed into a race and the race is pressed into the housing.”
It is generally understood that the two-piece rod end is created when the rod end body is swaged around the ball so that the race that the ball is in contact with is a part of the rod end body. It is less expensive to manufacture and provides adequate radial and axial strength in many applications. The three-piece rod end is a fully swaged bearing construction that allows for flexibility in types of materials that can be used in the component parts, which means that they can be made to meet almost any application.
The three-piece construction consists of a race that is formed around the ball, and then the race insert is staked into the body. In addition to different materials (stainless steel, aluminum, chromoly, and others), rod end construction often includes heat treating, chrome plating, zinc plating or cadmium plating.
Rod end selection should consider the angle of misalignment for most applications. Most manufacturers, like FK Rod Ends, publish a maximum recommended angle for the different types of rod ends offered. Not all rod ends can accept the same degree of misalignment and the manufacturer will publish specs in their catalogs. Failure to work within the manufacturer’s specs can lead to premature rod end wear to outright rod end failure.
When it comes to maintaining racecar rod end bearings, “Keeping it clean is the most important thing,” said Stacy. “Especially on the metal-to-metal (non-teflon lined) units. The dirt that gets ingested into the race loosens the assembly. This eventually wears the rod end beyond usable limits.”
Keeping it clean is as simple as using common products. “Clean rod ends with soap and water. Never ever use grease on a rod end,” advises Stacy. “The grease catches the dirt and makes things worse. If you feel the need to lubricate the rod end, a dry film lubricant can be used.”
For teflon lined rod ends, the maintenance is even easier. Stacy clarified the maintenance cycle on PTFE rod ends. “There is no maintenance on a PTFE rod end. The liner works as a lubricator and wipes the ball clean. Again, soap and water is best for cleaning and no grease is required.”
Inspecting the rod ends for replacement is another area where Stacy has specific advice. “As far as when to toss a rod end away I would say anytime the ball gets loose in the bore,” adding, “As the rod end wears the ball will get loose and eventually bind up on the bore.” There is a difference between a tight rod end and one that is bound up.
The rod end should be checked with a load and with the ball isolated. If the ball will not move and is bound up, it should be replaced, but if the ball turns but is stiff in the bore, it is in great condition. “The tighter the ball is in the bore, the longer the rod end will last,” explained Stacy.
“On a high-horsepower drag car, there are no telltale signs for when a rod end might fail,” he added. “Inspection of the rod ends on a weekly basis is advised.”
Our Project Car’s Rod Ends
Taking a page from FK Rod End’s best maintenance practices, we decided that our high horsepower racecar was worth the cost of rod end bearing replacement before the racing season began. Our stalwart crew removed the rod ends from the tie rods, front lower control arms, and the rear three-link controls. They checked each rod end for play radially and axially in the bearing area. Most of these rod ends were worthy of being put into storage as “back-up” rod ends in case of an emergency.
A complete set of rod ends for our outlaw drag car consisted of the following:
- Tie Rods: JMX7 (2) JMXL7 (2)
- Front LCA: JMX10 (4)
- Limiters: JMX6 (2)
- Three-Link: HRSMX8T (2) HRSMX10T (1)
Replacing the rod ends requires a deliberate procedure, according to our shop manager Sean Goude. “We take great care to inspect the rod ends after each race and clean them thoroughly. When it is time to replace a rod end, we remove the entire link and get a center-to-center measurement of the link before removing a rod end.” According to Goude, both rod ends will be removed even if they intend on replacing only one of the rod ends. “Once we have a solid center-to-center measurement, we remove both rod ends so we can accurately center the link with equal thread count on both of the rod ends during reassembly. This keeps the link centered perfectly while maintaining the correct length of the link.”
Because the rod ends are used on control links, Goude likes to have two sets of eyes check the work. “Like aviation mechanics, we use a system that requires an inspector to sign off on the maintenance when directional controls are broken apart and require re-installation.” Goude points out that good maintenance practices are as essential as routine replacement of the rod ends for safety. “When it comes to thread engagement to support the loads recommended by the manufacturer, the rule of thumb is a minimum thread engagement of one-and-a-half times the thread diameter,” said Goude.
When it comes to basic economics, replacing rod ends regularly is much less expensive than repairing or replacing a torn-up racecar due to rod end failure. Understanding which rod ends work for different applications, weekly cleaning and inspection, along with planned replacement will go a long way in protecting your investment and keeping your crew safe. For a component that appears to be very simple and uncomplicated, there is a lot to know about rod ends!