Replacing The Motor Head

Replacing the motor head is a frequently performed modification for a nitro-powered RC vehicle. It's also one of the easier modifications to make as well, because it's basically nothing more than a simple swap with rarely anything in the way. However before you jump right in and replace the head you need to make sure you aren't doing it for the wrong reasons, as many people often do.

You should never swap a motor head as a way to correct improper tuning. I often see many people who have problems with their motors overheating due to improper tuning or an air leak, and they think they can just swap to a bigger head and cure their problems. This will only mask the symptoms and problems they are experiencing, and in the end the motor may still suffer from a premature failure.

On the other hand, in the case of someone who runs in certain high heat or humidity conditions, a different head may help the motor to run cooler. This also applies in the cases of someone who may drive their truck with a heavier trigger finger than others. Keep in mind, however, that sustained periods of running wide open can still cause the motor to over-rev. An aftermarket motor head will do nothing to prevent that from occurring.

The head swap below is being performed on a 2.5 T-Maxx. However swapping the head on a Nitro Rustler will be very similar to what's shown below, no matter what motor you have. You will need to ensure that the new motor head is designed for the motor application you currently have however.

To swap the motor head, the first thing you'll need to do is to remove the blue glow plug wire. Then clean around the glow plug and then remove it.

Next you'll remove the black head protector ring that sits on the top of the stock motor head. All you'll need to do is to simply pull it straight up and it should pull right off.

Once you have removed the head protector, you can access the 5 bolts that secure the motor head. Using a 2.5 mm hex wrench, loosen the bolts by turning them counter-clockwise.

When the bolts have been fully loosened you can simply lift the motor head off of the engine block and what should be left is shown below.

Now you'll need to transfer the copper shim from the old head to the new head. The shim is shown in the picture below. Slide your fingernail under it and lift it off.

Once it's off you may want to clean it before reinstalling it on your new head. Keep track of which side of the shim was facing the head when it was removed, as you should reinstall the shim in the same direction as it was on the old head.

This picture shows the shim installed on the new head. A small coating of after-run oil, on the head side of the shim, will help hold it in place while you lower it into position on the motor.

Place the head on your motor block and then run the bolts down, but don't tighten them down.

When tightening the bolts down, you'll want to tighten them down using the following sequence shown in the figure to the right. Simply put, all you're doing is once a bolt is tightened, move to the bolt directly across from the one you just finished. You'll want the bolts to be snug, but you don't want to over tighten them and risk stripping the threads in the engine block. If you have a torque wrench that measures in/lbs. of torque, Traxxas recommends each bolt be tightened down to 9.7 in/lbs. of torque.

Since many aftermarket heads don't have a plastic head protector like the stock 2.5 head does, a few zip ties placed around the top cooling fin of the head will help protect it from damage should your truck ever turn over.

Once the head bolts have been reinstalled, all you need to do is to reinstall the glow plug and glow plug wire. Once that's done you're finished.