T-Maxx Motor Swap

The following article has been contributed by Klaüs, from the Traxxas forums. If you have any question or comments regarding this article you can reach him through the Traxxas forums, or via e-mail.

After hearing so many positive things about the O.S. .18 motors, I decided to research it a little further and see what it would take to get one into my Maxx. I bought my T-Maxx used, and even though the seller was very honest about the condition of the motor, I really had no way of knowing just exactly how many tanks were on it. Plus, when I first got my Maxx, I wasn't all that great at tuning, and I ran it pretty hot a few times. So, now that I have more experience tuning and had a good general feel for my Maxx, I decided that I would put a fresh new motor in it.

I choose the O.S. .18 CV-RX. Installation is really not all that difficult. You only have to buy a few extra parts and modify the crank shaft a little bit and you're good to go. Below I will try to detail out the steps I took in order to install the O.S. .18 into my 2.5 Maxx.

The first thing you will need to do is make sure you have all the correct parts. Below is an image showing the motor, and the clutch adapter nut that's needed. The clutch adapter nut is Traxxas part #4144 or Tower Hobbies stock #LXJF69. The O.S. .18 Tower Hobbies stock # is: LXGGP6.

Other than those two items above, in order to make this motor work on your T-Maxx you will need a new header/manifold. This is because the O.S. .18 is a "side exhaust" motor. The TRX 2.5 (and most other T-Maxx direct drop in motors) is a "rear exhaust". Many people just use their stock pipe, with a new 'side exhaust' header. I choose to get a whole new exhaust system. The system I choose is the RD Logics "61500" One piece exhaust system. This was an exhaust system designed for a 'side exhaust' motor.

Now that we know just exactly what we will need in order to make this motor work on our trucks, let's begin with the install. The first thing you will want to do is remove your TRX 2.5 motor. This is pretty straight forward, just remove the throttle linkage, the gas lines and the 4 motor mount bolts and it will just fall out.

Once you have the motor out, you will want to take the crank shaft assembly apart so you can re-use the parts on the O.S. .18. All of the parts will be used except for the motor itself, and the flywheel nut. When you get your motor apart, it should look something like this.

Once you get that complete, go ahead and set your TRX motor aside, and place all of the parts you just removed somewhere safe where they won't get lost. Now we start the fun part. You will need to modify the crank shaft on the O.S. .18 in order for it to take the clutch adapter nut we discussed earlier.

Figuring out where to cut is simple. All you have to do is temporarily install the flywheel. To do this, just simply slide the split beveled cone over the crank shaft, and then slide the flywheel overtop of that. Be sure that both are snug up against the bearing of the motor. Next, pull out your Traxxas clutch adapter nut and hold it up against the flywheel. This will tell you how much you need to cut off in order for the nut to do both of its jobs. This nut holds the flywheel in place, and also gives you a place to mount the clutch, and clutch bell assembly. The whole process should look something like this.

Once you have a good idea of where you want to cut, you may mark it with a pencil, or count threads, or just simply remember like I did. You will want to protect the motor so it doesn't get any metal shavings down in the sleeve. Without the header and air filter on, there are a few places where some large metal chunks could get inside your brand new motor and destroy it. To keep this from happening, I just simply slipped a plastic bag over my motor, and pushed the crankshaft through the plastic so I could get at it.

I then made sure my Dremel tool was ready, and had a good fresh cutting wheel on it. I would recommend a Dremel tool for this as any other larger tool, like a grinder may be too big for the job and you won't get the accurate cut you would with the Dremel. Once you are all lined up, have your safety glasses on and are ready to go, fire up the Dremel and git-er-done.

Be sure to clean up any metal 'spurs' that may still be on the cut end of the crank shaft, you want to make sure the threads are clean. Once this is done, take a deep breath and continue on with the fun stuff!

Now comes the time to pull out all those parts you removed from your TRX 2.5. You will now be assembling your clutch assembly on your O.S. .18. The image below shows the order in which everything goes. It will go on the same way as you removed them from your TRX 2.5, but with the addition of the clutch adapter nut.

Once you have your crank shaft clutch assembly all installed, it will look something like the picture below. This picture also has the TRX 2.5 next to it with the stripped crank shaft. The items as the bottom of the picture will not be used.

Everything from here on out is pretty straight forward. At this point, I installed my RD Logics header onto the motor, and the stock motor mount. I then installed the whole motor onto the chassis of my truck. Be sure to remember everything that is involved with this, like setting the correct spur gear/clutch bell gap. Once that was complete, I installed my RD Logics pipe. Doing this required a few extra things, like installing the front pipe mount. Things like this will all depend on what pipe/header you end up using on your truck. Once you are all done with this, it starts to look pretty.

After I got the motor and pipe completely mounted the way I wanted it, I went to hook up the throttle linkage. I ran into a problem with this in that the stock throttle linkage was a bit short for some reason. The stock throttle linkage was too short in that it would open up the carb all the way when the throttle servo was at its full throw. Some of the guys who also use the O.S. .18 did not run into this problem. Maybe you will, maybe you won't. To fix this problem, I used some spare RC turnbuckle parts I had laying around. I converted the throttle bell crank post to use a ball stud.

I then adjusted the turnbuckle to the correct length and installed it on my truck. The result was actually quite good in that the throttle response seemed to be more firm and accurate. Got lucky there! Once I installed the new throttle linkage, I was almost done.

At this point, I put my whole truck back together by re-installing my gas tank, air filter, and a few skidplates that I had previously taken. I also put new fuel line in as well as a new fuel filter. Once you have everything back together, you may want to turn your receiver and truck on, and play with the throttle servo a bit to see if any adjustment might be needed. Chances are it might. I took this opportunity to adjust my brakes as well.

Once you are done, the final product should look something like this!