AXLE INSTALLATION & REMOVAL
By Mike Burrell
We’ve all been there: taking the biggest dead-blow hammer available and beating the living tar out of an axle to try and remove it from a kart. And we’re not talking about a crash bent axle either we’re talking about trying to change a straight axle for tuning purposes. So why is it so difficult to remove and install an axle sometimes? Is there something wrong with your kart or your procedure for installation? Or is this just “part of karting?”
Changing an axle should not be able to be counted as a cardio workout. At a recent 2009 Kart Product Launch, we were amazed to watch the Italian “super-tuners” change an axle in eight minutes from the time the kart stopped to the driver launched back to the track! According to the manufacturer, this amazing feat was accomplished because “the axle was put in right the first time.”
Installing an axle properly before you leave for the track is something that will take a little time to do in the garage, but will pay huge dividends at the track when it’s time to change the axle. In the remainder of this article we will go through the proper steps to remove and install an axle, provide tips for making axle changes more time efficient, and help troubleshoot an axle that is being difficult to remove or install.
Why changing an axle requires a large rubber hammer:
In a perfect world, changing an axle would just require the removal of the bearing set screws, the removal of the wheels and hubs, and the loosening/removal of the brake rotor carrier and the sprocket carrier. Everything else (bearings, cassettes, cassette hangers, frame) would be perfectly aligned and free enough to shove the old axle out one side of the chassis. Often –no, rarely, does that happen.
There are a number of reasons an axle doesn’t just slide out. Most often, something is “bound up”. In other words, something isn’tstraight causing the already tight tolerances between the axle and the inner bearing races to be even tighter. Questions to ask oneself about why an axle would be bound up include: was the rear of the kart crashed since the last axle change or are the cassettes equally torqued in the bearing hangers? It only takes one cassette bolt that pulls the bearing hanger and cassette slightly from the straight position (perfectly perpendicular to the axle) to bind the axle up.
A way to check for axle bind before trying to remove the axle is by installing a minimum number of bolts in the cassettes, say two each, lightly torquing them and spinning the axle. Provided the bearings are good (and that’s a whole other story) the axle should spin freely and easily for a few revolutions. If the axle is spinning free, properly torque the cassette bolts and install the remaining bolts one at a time checking the free-spin of the axle between each.
One other piece that binds quite often is the brake rotor and its carrier. The brake rotor creates immense heat while in use, and this heat is transferred down into the axle causing the two to seize slightly. Also, the load (twist) a rotor puts on an axle under braking can essential ‘pre-load’ the axle/rotor carrier causing bind. Two simple tips to try and reduce the seizure and eliminate the bind are to use a thin layer of anti-seize lubricant between the axle and rotor carrier. If it’s difficult to slide the rotor and carrier when the carrier bolt is loosened, try loosening the actual rotor from the carrier.
Another reason an axle might require a hammer to uninstall is the over-tightening of the bearing set screws to the point they dig into the axle causing burrs or flat spots (crush points). “Burrs are the big one, not just from the set screws but also from around the recesses around where the keyway goes,” says Mark Ouimet, from SSC East. “I keep a small file near by to file down set screw burrs while the axle is being removed.”
No one wants their axle to shift while on track, but it also doesn’t do any good damage it for future use. In reality it doesn’t take much torque for the set-screw to hold an axle in place. Instead of over torquing an axle set screw, try using a drop blue Loc-Tite to assure the set screw won’t back off.
“Another reason we see for straight axles being difficult to remove are the ends of the axle being ‘mushroomed’ from being beaten in or out and excess plating on the axle,” states Keith Freber owner of Margay Karts. “When removing or installing the axle used a soft faced mallet (if necessary). If you take your time and do things right, you shouldn’t need a hammer at all. Take special care with thinner wall axles. It’s very easy to distort the ends.”
However, there are certain times you need the soft-mallet and there are other times that the axle stops moving at the bearing without the axle being able to slide out. There are tools to move the axle outside the bearing. “In the past I have taken old bent axles and cut off a six inch section from the straight section,” continued Ouimet. “Then while getting a axle out if I get to the bearing I can use this piece that I have cut to push the axle through the remainder of the bearing.”
Install It Right the First Time:
Now that we know a couple of the reasons why an axle is difficult to remove, we need to understand what we can do during the install process to make changing an axle easier in the first place. With axles becoming more and more important in the tuning process, it’s becoming essential to be able to change them between on-track sessions not just at the end of the day.
As was stated earlier: if an axle goes in straight the first time, it should come out straight and easy. There are some general assumptions that need to be made before going any further with this article; we must assume the axle and the frame are straight. If either is even the slightest bit tweaked, skewed, or bent that could result in the binding affect that is encountered during installation and removal.
Freber reiterates the importance of “pre-installing” a new axle before leaving the garage to make it easier changing at the track: “Install the axle, tighten the set screws just enough to mark the axle, remove the axle and file a small flat where each set screw makes contact. Be sure to re-install the axle with the set-screws properly aligned.”
At this point, the axle of the kart is removed so there is no better time to clean the chassis and prepare the bearings for the new axle. “Clean, Clean, Clean while the axle is out it is a perfect opportunity to clean up the back end. Check for any imperfections, burrs in the bearings that the axle may get hung up on,” states Ouimet. One effective way to prepare the bearings and assure they are free of burrs is to use a ball hone on the end of a drill. Ball hones can be purchased in about any diameter from many industrial supply stores and specialty tool shops. Fifteen minutes with the ball hone and some WD-40 can assure the bearings are clean of burrs and of the correct diameter for the axle.
As mentioned in an earlier paragraph, sometimes the plating on an axle increases the diameter more than the manufacturer intended; this also happens on the inside diameter of the bearings. To reduce the thickness of the plating, even a ten-thousandth of an inch, karters may be required to use Scotch-brite or another very fine abrasive on the axle. “Make sure there are no burrs in the bores of your hubs. Pay close attention to the edge of the key slot,” says Freber. “Clean the bores with WD-40 and Scotch-brite.”
Once you are assured the bearings and axle are free of burrs and the diameters of the axle and bearings are correct, it should be easy to reinstall the axle. If the chassis has a third bearing, loosen that cassette for installation. Test-install the axle through the inside, third (middle), and outside bearings; assuming it slid in and out freely it’s time to try and install it with the brake rotor.
Often, when the brake rotor and carrier are added to this equation is when the axle becomes more difficult. Some tuners suggest loosening the rotor from the carrier; if you choose to try this –be sure to tighten the rotor back up after the installation is over. Another option to assure the brake rotor fits properly is to again check it for burrs on the inner diameter and use a lubricant such as WD-40 to make installation easier.
Something else to remember when installing the axle for the final time before hitting the track: don’t forget the brake rotor key or the water pump o-rings (if applicable). No matter how many times a mechanic has changed axles, every now and then even the best forget the brake rotor key or o-rings.
Now let’s look at proper axle installation in a step-by-step manner. We will begin this process with the axle free of burrs, clean, and out and the bearings and rotor/sprocket carriers cleaned and honed (or polished free of burrs).
1.“Loosen the third bearing before removal or installation,” states Freber. “And only tighten it after you have tightened the set-screws in the two outer bearings.” Additionally, consider only having three of the outside bearing carriers bolts installed in each side. Some carriers now come with up to six mounting points for added tuning; if you desire more than three, they should be installed later (see step eleven).
2. Lubricate the inside diameters of the bearings and rotor carriers either with high-temperature assembly grease, anti-seize, or a generous flow of WD-40. “It is common to use a lubricant on the axle when removing it, don’t forget to leave a spot “unlubricated” so you will have a spot for a good hand hold,” stresses Ouimet.
3.Insert the new axle from the engine side through right side and third bearings. This should be rather easy, especially with the third bearing loose.
4.Install water pump o-rings if applicable.
5.Position brake rotor in caliper (double checking the direction of the rotor as this matters for proper key placement with some axles).
6.Continue guiding the axle through towards the brake rotor carrier and gently begin to push it through the rotor carrier. It may be easier to turn the axle as it goes through the carrier to help assure it goes on straight and not slightly cocked at an angle.
7.Align and begin to move the axle through the left side bearing. If excessive force with a rubber mallet is required at this point, chances are there is an alignment issue (slightly bent frame, ride height difference, etc.) that requires immediate attention.
8.Don’t forget the brake rotor carrier key!
9.Assuming the axle is through all three bearing carriers, rotate the loose axle to align the previously made (see above) flat-spots for the set-screws. Also, at this point the axle needs to be measured from each outside bearing to the axle tip to assure it’s centered in the chassis.
10.With the axle centered, it’s time to install the set-screws in the outside bearings. Using a drop of blue Loc-Tite, install and tighten all the outside bearing set-screws –but don’t over tighten them and damage the axle!
11.With the outside carrier set screws in place, it’s time to tighten the third bearing if applicable. Tighten the third bearing carrier bolts, one at a time, while spinning the axle to assure no bind is being added to the chassis. Also at this time, if you desire more than three bolts to hold in the outside carriers add them one at a time. Be sure to keep checking the axle’s free-spin to assure none of the addition bolts are adding bind.
12.Install the third bearing’s set-screws (if desired) in the same method as step 10.
13.Center and tighten the brake rotor carrier.
14.Double and triple check the axle spins as freely as it did when it was just slid through the two outside bearings!
Reducing drag in the axle is like adding horsepower to your engine, and usually a lot cheaper and easier. Proper axle installation is essential for minimizing drag and for ease of removing the axle –one of the strongest tuning tools karters have at their disposal. Possibly the best a karter could take regarding axle installation comes from Freber: “Take the time and pre-install all of your axles. This should help you avoid the embarrassment of asking your pit neighbor for a larger hammer!