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Maintenance Guide

This page was created in response to the requests from a few hobbyists for some sort of maintenance schedule. We've tried our best to make these tips apply to everyone, but where different R/C hobbyists require different maintenance schedules for the same item, we listed the general hobbyist's needs first, then address the racer's needs. These tips are great for those new to the hobby, and are great reminders for experienced racers, too! This page covers every topic about electric and Nitro cars, from batteries and motors to cleaning bearings and rebuilding diffs. It's a great resource for racers at any level!

Beginners please note: On this page and throughout the site, the term "run" when talking about electric cars refers to running the car for a full battery pack, until the pack is discharged. When the term "tank" or "run" is used in reference to Nitro cars, it refers to running the car for one full tank of fuel.

Check out our R/C Glossary, perfect for a starting point to figure out all those R/C terms you're hearing everywhere.

General Maintenance - applies to all cars

General Cleanliness - A clean car is a happy car! Not only that, but you will be able to spot problems easier on a clean car than on a dirty car, and also while cleaning it, you can give the car and body a quick look to see if anything is wrong. Use a large natural-hair bristle brush (from a hardware or paint store) to remove dust from the chassis and inside of the body. Use some denatured alcohol or motor spray to clean off tyre and asphalt marks from the outside of the body.

Differentials - These let the outside wheels in a turn spin faster than the inside wheels, so the car can maintain the proper path when turning.

For cars using gear differentials, you should check the areas around the diff shafts for grease leaks every 20 to 25 runs. If you see a leak, you need to take apart the diff and put more grease in it, and reassemble it carefully.

If you run a car with ball differentials, you should check the diffs for grittiness every 5 runs or so. To do this, put the car on a stand so the wheels can rotate freely. Hold the spur gear and slowly turn a wheel. Try to feel if the action is smooth or 'gritty'. If it feels gritty or the wheel is difficult to turn, you need to rebuild that diff. Now check the other diff using the same technique. You can use diff rings and thrust washers twice - just flip them over to a smooth side. If you don't have a smooth side on the rings or washers, you need to buy new ones. We don't recommend using diff balls and thrust balls through more than one rebuild - you should replace these each time you rebuild a ball differential. Carbide diff balls will last longer under the same circumstances as regular diff balls.

Shocks - Shock absorbers soak up bumps in the track and let the tyres maintain constant contact with the racing surface; they also let the tyres dip into depressions in the track. If you are a 'backyard basher' or casual hobbyist who doesn't race, you should give your shocks a look over before each time you run the car. If you see any leaks, you need to rebuild your shocks. When rebuilding shocks, you should always use brand new o-rings. Never re-use old o-rings!

Racers should check their shocks before and after each run. Any leaks mean it's time for a rebuild. Shocks on a racing R/C car should be rebuilt or given a good look every ten or fifteen runs. Be sure you write down what shock oil you are using in the car! Either write it on the shock cap in a fine-point permanent marker or use one of the HPI Setup Sheets . When rebuilding shocks, you should always use brand new o-rings. Never re-use old o-rings!

Drive Pulleys - These either turn the belts (on the gear shaft) or the belts turn them (at the diffs). Whether you race indoors or outdoors, you should check the teeth of each pulley before the day's racing begins for any rocks, tyre debris, tape, etc., that get stuck in there. Use a hobby knife or a dental pick ('teeth' cleaner, get it?).

Drive Belts - Provide a way for power to be transferred from the gear shafts to the diff pulleys. The belts should be replaced if you notice any significant wear on them (if you can see threads hanging off the belt, that's significant!). Also, if the belt gets so loose that no amount of tensioning helps, you should replace the belt. Belts are a wear-and-tear item; they must be replaced periodically, just like the belts on a real car!

Belts should not be "guitar string tight", they should be loose enough that you can wobble the belt up and down, but tight enough that the belt does not slip off a pulley under braking or acceleration. For the most part, the rear belts won't have to be adjusted, but the longer belts (front belt, in other words) will need to be adjusted periodically for most cars.

Bushings - Used on most rotating parts on sport or budget kits, bushings are better than direct contact between the parts, but not as good as ball bearings. Bushings don't need any maintenance to speak of, just keep them clean and grease them when they are first installed.

Ball Bearings - Used on most rotating parts on pro-level kits, bearings provide a way to eliminate almost all of the resistance that bushings have and serve to make the car quicker overall. For HPI kits with the standard shielded bearings (metal shields on the side), just brush them off every now and then. You may want to put a very light dab of oil and let it soak into the bearing, but for the most part just brushing the dirt off the bearing is fine. HPI's more recent kits now include rubber sealed bearings, which require even less maintenance. All HPI kits that include bearings already are being upgraded to rubber sealed bearings.

Gear Mesh - The relationship between the primary drive gear (pinion or clutchbell) and the secondary drive gear (spur gear). A tight gear mesh (the spur cannot 'wiggle' when installed) has too much friction and will cause the motor or engine to work too hard and could melt the spur gear from the friction. A loose gear mesh (the spur can move significantly) will probably cause the pinion gear to strip the spur gear, ruining the spur gear.

To set a proper gear mesh on electric cars, use a small piece of normal notebook or copier paper and put it in between the pinion and spur, and tighten the motor onto the motor mount. Remove the paper, and that is how much gear mesh you should have. For Nitro cars, you can get away with a little bit looser gear mesh than on electric cars because the gear teeth are much larger. Use the same technique described above, but fold the paper once before you put it in between the gears.

One-Way Diffs - Many racers do not lubricate the one-way differentials as often as they should. Every few runs, you should take the one-way diff out and remove the gear shafts to inspect the bearing. If there is no hint of grease on the bearings you should use a very small amount of the blue-capped grease that comes with the one-way diff (the amount of grease that would end up on a toothpick or pin if you dipped it in the grease) and re-lubricate the one-way bearings inside the main diff body. This will help prevent a major cause of one-way diff failures. Crashing and no lubricant are the main reasons why the one-way bearings in the one-way diff break.

Electric Car Maintenance

Motor - The powerplant of an electric car, the electric motor requires proper maintenance to run smoothly and efficiently. Motors have many maintenance-intensive parts; we will deal with each one separately.

Motor terms: First, however, we will go over the basic parts of the motor. The can is the metal main body of the motor. The motor magnets are glued to the inside of the can. One bearing (for modified motors) or bushing (for some budget modified or stock motors) is at the end of the motor can, where the motor shaft comes out.
The endbell is the plastic part of the motor that seals the motor and has another bearing or bushing where the other end of the motor shaft sits. The brush hoods hold the brushes on the endbell, and the motor springs hold the brushes against the commutator. The brushes are the only parts of the motor that touch the commutator, and are very important in modified racing. Every brush has a shunt wire, which is how the brush is connected to the brush hood. Solder them on for maximum efficiency, or use screws and eyelets for convenience. Most brushes are available with or without eyelets. Some endbells have heatsinks built into them, and others have inspection holes so you can check the commutator without taking off the brushes. Some endbells have both features. The endbell also has the motor tabs, where the motor wires or connectors are soldered.

The armature sits inside the can. The armature includes the motor shaft and all the stuff that spins inside the motor. The commutator is the copper part of the armature, and is only part that most racers have to worry about. It must be in good condition for good performance and high efficiency. The armature also features copper wire wrapped around laminated stacks of metal that are cut into distinctive shapes called poles. All stock motors have the same number of winds (wraps of wire around each pole), while modified motors have less winds with thicker gauge wire for more power and RPM (Revolutions Per Minute).

Now that the motor terms are out of the way, let's move on to motor maintenance!

Cleaning - You should purchase a can of motor spray (HPI's Nitro Car Cleaner is a good bet) and a set of commutator cleaning sticks. Remove the springs from the endbell, and then take out the brushes. Don't lose the springs! Holding the motor with the endbell facing down, spray the commutator from three or four sides (rotate it if you have to). Let the motor spray dry, then insert the square end of the blue or red comm stick and hold it lightly against the commutator. Rotate the motor shaft several times to let the comm cleaning stick do its job. Then do the same thing with the green (polishing) comm stick. Racers should clean the motor after every run, casual hobbyists should do it at least every two or three runs.
We'll cover cleaning the brushes when we get to the section on motor brushes.

Commutator Truing - If you don't race, you should have someone true the commutator of your motor (whether it's a stock or modified motor) every ten to fifteen runs. Ask your hobby shop if they true motors there, or find a racer who is willing to help you.

If you are a serious racer, you should have your comm trued at least every four to five runs. The more often, the better. Having more 'shallow' cuts more often is better than just a few 'deep' cuts. After each cut, you should replace the brushes as well, since the commutator has a new profile. Backyard bashers won't have to worry too much about replacing the brushes, but it should be done when the brushes are noticeably worn down.

Truing the commutator and replacing the brushes basically 'refreshes' the motor and makes it run pretty much like new, so it's a highly recommended procedure!

Motor Brushes - The brushes on your motor should be cleaned when you clean the commutator. Use the motor spray to clean the ends of the brushes, and then use the round end of the blue or red comm sticks to clean the face of the brushes. Rotate the sticks, don't move them up an down on the face of the brush! Then use the green comm stick to follow up the cleaning.

About brushes and comm truing: Casual R/C hobbyists won't need to replace the brushes on their motors very often, only when the brush gets worn down to about 2/3 its original length. Using serrated-face (quick break-in) brushes is fine for the 'backyard basher'. Racers, on the other hand, should get a new set of brushes every time they have the commutator trued on their motor. This allows the new brushes to re-seat themselves on the new, smaller comm diameter. The race-style brushes that don't feature a serrated face are best for serious racers, since the serration breaks in quicker, but causes a little extra wear on the commutator that racers may not like.

A note about high silver content motor brushes: If you use a motor that has high silver content, you should know that those brushes should be replaced every two or three runs because they wear very quickly. They are meant for serious racing only! If you are a casual hobbyist and bought a motor that has these brushes in it, you should replace them with an economical pair of brushes when the originals wear out.

If you run your motor in very hot conditions (no cooling air, high gearing, etc.) there is a chance your brushes could be damaged. If the brushes, commutator, endbell or brush springs look discoloured after a run, you need to take it easy on the motor, or it won't be able to run much longer! Remove the inner body or use a smaller pinion or larger spur gear when running the car with that motor. Beginners need to be especially careful with modified motors, because the gearing for them must be lower than for stock motors.

Brush Springs - Most R/C hobbyists shouldn't need to ever replace the springs on the motor. If you run the motor very hot (see above) there is a chance you can damage the springs so that they don't maintain the same tension on the brushes. A sure sign you are running the motor too hot is that the brushes come unsoldered! If this happens you will probably have to replace the brushes and springs, as well as true the comm, to get the motor up to normal operating standards.

Bushings and Bearings - Use an oil specifically made for bushings or bearings, and completely fill up the end cavity where the motor shaft sticks out on the outside of the can and endbell. Fill one end of the motor, spin the shaft a little, then fill the other end. Oiling the bushings of a stock motor is very important, since not oiling them can cause extra friction you just don't want!

Batteries - Many racers follow a myth that there is a science to charging and discharging batteries. Here is the simple truth:

Charging - Use a peak-detecting linear charger to charge the batteries at 4 amps. That's it!
Battery chargers that use a timer, or feeling the warmth of the batteries is nowhere as exact as peak charging, but for casual R/C drivers, it gets the job done. The HPI Team Drivers at the ISTC World Cup charged their batteries at 4 to 5 amps.

Discharging - For 95% of racers, all that is needed to discharge the battery after running is to run the car until it is very slow, then take the battery out and let it and the motor cool down.
If you don't have time to run the batteries down (for instance, at organized races where you can't run your car when it's not your race), you can use a single 12 volt automotive light bulb (#1157 standard type bulb) to discharge the battery pack. Some racers feel that using 30 amps to discharge the batteries after a race allows them to gear the car better, but with later batteries such as the RC3300 and RC3000, runtime is much less of a factor, especially in stock class racing. Modified racing is a slightly different story - you still have to know how to gear the car to avoid dumping.

The reality is that it is easy to listen to experienced racers go over the 'proper' way to charge or discharge a battery, but you should know that there is no need to over-analyze the simple process of charging and discharging a battery pack. Properly cared for, a battery pack (even a cheap one) will last you for many years.

Nitro Car Maintenance

General Cleanliness - Use a spray like HPI's Nitro Car Cleaner or undiluted Simple Green to clean the car of grease and road grime, and keep a natural bristle brush handy to clean dust off the body and chassis between races.

Engine - The powerplant of the Nitro car and most of its weight. The inside of the engine should be checked for excessive wear by an experienced Nitro racer every 2 gallons of fuel or so (or 100 hours of running time on the engine). You may have to put in a new piston and sleeve, but after that the engine will run like new! You also should use After Run at the end of each day's running. Do NOT use WD-40 on the inside of your engine! After Run will absorb the water in the engine, not just displace it. Just follow the directions on the After Run bottle.

Ball Bearings - Make sure they are clean on the outside. Wipe them free of any grease from the exhaust and 'road grime'. Check the bearings after each day of running.

Nitro Two Speeds - The one-way bearing in the spur gear needs to be checked and lubricated every ten to twenty runs. Use the blue cap grease that comes with the front one-way diffs or some good quality lithium grease. Just a light coat is required to properly lubricate the bearing, so don't use too much!
Brake Disc - The only way you can stop your car, unless something bad happens to your brakes (in which case, a wall is the only thing that will stop the car!). Before each day of running, you need to check the condition of the brake disc itself, the brake linkages, screws and spacing of the screws holding the brake pads.
Screws - Since they hold the car together, you should check all the screws every couple of days of running the Nitro car. They should be tight and not stripped out. Replace the plastic bulkheads if the screws are loose and won't tighten. Use Loctite on all metal-to-metal screw connections (the motor mounts, etc.).

Serious Racing

This section is for those racers who are very serious about their racing! So don't be surprised if you see a suggestion here and wonder, "Do people actually do this?", because they do! These suggestions are not for beginners or casual racers! These tips assume you have a good knowledge of your car and are comfortable with taking it apart and reassembling it. Some of these tips will cost some money, and we are NOT trying to bankrupt racers, just give them a reference to check before they go to a big race or event.

Plastic Bulkheads - Over time, these will loosen and get weaker. If you constantly tighten and loosen the screws going into these plastic parts, you will accelerate the wear. To help prevent chassis tweak during races (wrecking), these parts should be as new as possible. Replace them before major events and use new screws if possible.

Hingepins, Shock Shafts and Kingpins - When tearing apart the car, check these parts. If you roll them across a piece of flat glass or countertop and notice a wobble, replace the offending part! Otherwise it will be binding up the suspension movement. Before a big race or when tearing apart your whole car, it's a good idea to use put the hingepins in a rotary tool and polishing them with some polishing compound on a rag.

Ball Cups and Shock Ends - If you have any play (side-to-side, or lateral play; this doesn't refer to the 'looseness' of the ball cup) in these parts you need to replace the plastic part so you get a more responsive suspension setup. Some racers build up layers of CA glue inside the ball cups to get a tighter fit on the ball ends.

Ball Ends - If you have a scratch on a ball end, you'll need to replace it. That scratch will catch on the plastic ball end or shock end and cause it to bind.

Ball Bearings - Some racers getting ready for a big race will clean out the thick grease completely from the bearings (soaking overnight in grease solvent or Simple Green usually does the trick - follow it up with blasting the bearings with motor spray or brake parts cleaner). With all the manufacturing grease out of the bearing, apply a very light amount of miniature bearing oil to the bearing, and that's it. Some racers go so far as to remove the side shields from their bearings to remove the extra friction caused by them.

Shocks - You should rebuild the shocks more often than the casual racer. A very important point that is overlooked by most racers is to make sure the shock's overall length is the same from left to right. Some racers have different length shocks front and rear, so make sure that at least the left and right shocks at each end are the same.. This helps make sure the car is not tweaked to the left or right. Trim the shock ends properly so there is nothing sticking off the ends (a file or emery board works great on the rounded ends), and use a set of callipers to measure the total shock length. The length can be adjusted by turning the plastic shaft end, the 'eye' piece that snaps on the ball end.

Racer's tip: You can replace the ball ends that hold the ends of the shocks with HPI #A133 (Ball 3 x 5.8 x 6mm) or the similar Associated part (6471, 7217 or 7660) and use screws to hold the shocks in. From the #6817 Shock Parts Set, just use the eyepieces that are slightly larger than the ones called for in the instructions (you've always wondered what those were for, didn't you?) and substitute them for the stock eye pieces. Just be aware that by using these, you will extend the overall length of the shocks, and you will have to adjust the ride height accordingly.
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