Losi XX4 Modern Racer build

[Lavigna]

This is planned to be a high end XX4 with modern electronics, running a 13.5 brushless motor.

This project has been in the pipeline since before I finished my early version XX4 shelfer, several years ago. I have been gathering parts for the past several years, but a clean solid graphite XX4 chassis kept alluding me.

I finally found a very clean solid graphite chassis in the form of a very clean original XX4. I also found a well worn XX4 with some upgrades and tons of spares. Both of these cars, combined with my stash of parts and upgrades will hopefully combine to make a great result.

[Lavigna]

A big goal of mine on this build is freeing up the drivetrain drag and reducing friction. When I spun the wheels on both XX4's before I tore them down, I was surprised by how much drag there was.

I got a set of Avid ceramic bearings. I am also replacing the plastic rollers with small 3/32 x 3/16 bearings.

I built up the differential driveshaft and roller assembly with a combination of new parts, and the best pieces from both donor cars. Both are using the upgrade aluminum shafts.

[juicedcoupe]

The only thing I don't like about ceramic bearings is how loud they are.

I have Boca ceramic hybrids in one of my reels. It sounds awful when you cast it. At first, I thought that I screwed something up while switching bearings.

But once you get used to the noise, it casts like a dream.

[Lavigna]

^ Juicedcoupe - Interesting. I didn't know that was a thing with ceramic bearings. The cost of ceramics is kinda crazy, but guys running modern stock classes swear by them as a big improvement. I was pretty shocked by how much resistance there was in both XX4's when I spun the drivetrain. Maybe they were both in need of correction, but it made me really prioritize reducing resistance on this build.

Getting both differentials completed was a big step. At first I was going to use Barracuda Ti outdrives front and rear. However I changed my mind and went with the composite drives up front. They are significantly lighter.

I am using Avid ceramic ball diffs and thrust assemblies. I sanded new drive rings with 600 grit, as suggested for these ceramic ball diffs. Both came out quite smooth. Glad to have the main drivetrain assemblies and diffs built.

[Lavigna]

Progressing. I got the belts in and main cover on. I've done everything I can think of to reduce drivetrain friction, but it still feels like a lot of drag. The rear belt is quite tight, as it's supposed to be, so that must be causing much of it.

I shortened the set screw that goes onto the slipper shaft so it's about even with the aluminum adjustment nut. I think it's a cleaner look, since it protrudes from the body.

[Lavigna]

Steering - I wanted to improve and strengthen the stock steering. I am using the upgrade aluminum 22-4 steering arms. To make them work in the XX4, I had to turn down the post to fit the standard bearings of the XX4.

I'm also using this Fox Pit Stop carbon fiber steering rack. This rack requires trimming of the front of the chassis for clearance. The whole process of making these items work together took some decent time and work, but I think the result was worth it.

[Retro rc]

Just wondering what belts your using? I have a nib xx4 I was starting to build when I found the belts were just a pile of powder

[Lavigna]

^ Retro RC - I believe these are Tough Racing or Bando belts.

I am using this Rusti Designs front aluminum bulkhead. I am so happy I ordered it when I did, as they are now going out of business, and all parts are sold out. It is very similar to the Trinity unit.

I realized that I had the carbon steering rack on backwards.

Front end is now bolted up, and towers are next. Just waiting on an order of Lunsford hardware.

[Mark Westerfield]

I tried running those Barracuda titanium outdrives in a XXT and the slots showed signs of wear after the second run. I would suggest using them for shelf display cars. With the plastic outdrives with those aluminum saver rings, you'll notice that the dogbone cannot slide straight into the saver ring, and the dogbone needs to be put in at an angle. I grind down the end of the dogbone pins VERY slightly so the the dogbone can slide in and out straight without catching on the ring. During racing, if you pop a ballcup or have too much droop, the ring will get bent and stretched if the dogbone comes out. Or you can slightly file the ring where the slot and pin travel, and glue the ring in place so it doesn't rotate. I've been using the plastic outdrives successfully in the front and rear of my XX4 and XXX4 with 10.5 power at the VONATs races for several years now.

[Mark Westerfield]

Also, with the belt rollers. The bearings for the steering are slightly larger in diameter than the standard plastic rollers. And I've noticed the tough racing belts are constantly contacting even the smaller diameter plastic rollers, increasing drive train drag, at least with the rear belt. I just use the 'A' bearing holder in the long position for the tightest belt setting, no rollers. The plastic belt rollers work good on the front belt. The belt should only make contact with the rollers when/if the belt tries to skip, not constantly.

[Lavigna]

Great info. Thanks Mark!

I've seen some folks replace the metal drive pins with the same length of weedwacker line. It holds up well and doesn't deform the titanium outdrives. I'm going to give it a try.

Good idea on the fronts. After I see how it lays out, I may try it.

[RogueIV]

^ Retro RC - I believe these are Tough Racing or Bando belts.

I am using this Rusti Designs front aluminum bulkhead. I am so happy I ordered it when I did, as they are now going out of business, and all parts are sold out. It is very similar to the Trinity unit.

I realized that I had the carbon steering rack on backwards.

Front end is now bolted up, and towers are next. Just waiting on an order of Lunsford hardware.

You should check out Schumacher CAT SX front arms they have a much stronger design and the same geometry as the originals. You just have to use slightly longer inner hinge pins.

[Lavigna]

^ RogueIV - Thanks for the suggestion. I have seen quite a few guys using these arms as replacements. I am going to keep the original arms for the time. I have several sets, and I like their rigidity compared to the Schumacher arms.

I am using Rusti Designs shock tower stiffeners front and back. The fronts are mounted. I trimmed off the outermost 2 holes. I like the aesthetics, and I'm hoping it will decrease the likelihood of the towers cracking in a roll over.

[Lavigna]

I changed the Exotek steering horn to the "B"option. This makes a proper right angle to the arms, and should provide consistent throw to left and right.

[Lavigna]

Plugging along. I'm using MIP aluminum front CVDs. Unfortunately the anodizing was so dark, they basically looked like steel. So I polished them up for some added bling.

I also reluctantly cut open my sealed package of Lunsford XX4 king pins. This was a very hard item for me to find.