HPI Racing - Nitro RS4 MT Building Tips

New!Engine Break-In Tip
New engines may lock up if the piston cools down when it is at the top of the stroke. To get it loose, heat the case with a hairdryer, remove the glow plug and apply a few drops of Marvel Mystery oil insided the combustion chamber.

Always try to move the piston to the bottom of the stroke after you have run it, you can feel it by turning over the flywheel. The top is the tight spot.

Important - Thread lock your engine pilot shaft!
Before starting any assembly on your kit, remove the pilot shaft from the engine (if it is preassembled already), put a drop of thread locking compound on the threads, and tighten down the pilot shaft as much as possible. Let it dry for the entire time you are building the kit, at least overnight (12 hours). This will make sure that the pilot shaft won't vibrate loose while you are running your kit.

Neat Wiring!
A neat wiring job not only looks "professional", but it makes your Nitro MT easier to clean up and makes it easy to install the radio tray.

Fuel Tank Bushings
Use old shock o-rings to cushion the fuel tank and prevent bubbles in the fuel line.

Loctite!
One of the first things you should get when you get your first Nitro kit is a small bottle of Loctite brand thread lock. Use the blue (242) compound thread lock, as it allows you to remove the screw from the hole when you need to. On any Nitro car, ALWAYS use threadlock on any metal-to-metal screws, including: engine mounts, steering pilot shafts, brake cam set screw, clutchbell screw, 2 speed set screw, muffler or header mounts, as well as any aluminum parts you may have installed. This is a critical part of the assembly of any Nitro car, and thread lock should be a standard part of your tool box.

Check for loose screws!
Before running your Nitro car or truck, ALWAYS look over your car to see if there are any loose screws or nuts. Many races have been lost because a wheel fell off a car, to the embarrassment of the driver! Check all the screws and nuts throughout the car to prevent damage to your car or embarrassment to yourself.

For the Nitro MT 2 Speed
We have had reports from some Nitro racers that they are damaging the one-way bearings in the spur gear of the 2 speed transmission. This is usually due to the fact that the bearing has gotten dirty, and/or the one-way bearing has no grease to lubricate it. If you have the #A906 Front One-Way Diff, you can use the dark grease (with the blue cap) to lubricate the one-way bearing in the 2 speed assembly. You can also use the Associated black diff lube. Lubrication of the 2 speed one-way bearing should be done every couple of hours of running, or every time you tear apart the car during routine maintenance.

Trouble Restarting
If you are having trouble re-starting the engine after is has run for a little bit, there are a couple of things you can do: 1) open the needle valve 1/2 turn and re-prime the engine, or 2) wait for the engine to cool down and start it up again later. The reason why you may need to do this is because the carb gets very hot as the engine is run, and if the engine is stopped for some reason and you have to re-prime the engine, the heat from the carb could evaporate the fuel before it gets a chance to get inside the engine.

Use gasket sealant
When assembling the muffler and attaching it to the engine, we've found that Permatex RTV Silicone is great for preventing fuel leaks. It also helps to make sure the screws that hold on the muffler are very tight.

Click here to see a larger version of the above image

Air holes in wheels
Use a small drill bit to put two small air holes in each wheel, opposite each other. This lets air inside the tires in case the tire is glued all the way around the tire making it almost airtight. If a tire that is almost airtight is compressed, the tire may not fill back up with air and expand, giving you a temporary flat spot on the tire. A couple of 1/16" holes will prevent that problem.

Clean wheels and tires before mounting
Use rubbing alcohol or motor spray on a rag to clean the rims where you will be gluing the tire to the rim. Doing this will ensure a good bond so that your tires do not come off during a race.

Use thin CA for tires
HPI racers have found that Pacer Zap CA (CyanoAcrylate, or Contact Adhesive) works best to bond the rubber of the tire and the nylon of the wheel. It is super thin, and it runs very well between the tire and rim. It may run too well, so don't use too much, and have some debonder (super glue solvent) available in case it gets on your fingers.

Graphite parts
With the woven graphite option parts, you should remove any sharp edges with fine-grit sandpaper. Make sure the edges are rounded so that the graphite edges do not cut through your wires and short-circuit the electronics.

Follow the break-in instructions!
Make sure you break in your engine correctly! Do not give the engine any throttle or run the rpm's very high at all. The whole idea of breaking in the engine is to seat the washer on the head of the engine head and wear in the piston and sleeve. If you run the engine at high rpm's during break in, you may find it very difficult to start the engine.

Stalling problems
If your engine stalls at idle speed or after you take off the glow plug igniter, you probably have a bad glow plug. You should get an O.S. #8 glow plug, it is a very good all-around plug and should last a long time. If the engine stalls at mid-throttle, you are running too lean. Back out the needle valve a couple of clicks, and try again. If the engine stalls at full throttle, you are running too rich. Close the needle valve a couple of clicks, and start the engine again.