Kraton Newbie to Arrma (but not to RC). Kraton 6S "Sand Scorcher" Build...Input/advice welcome!

[EsotericRC]

As the title states, I'm a newbie to Arrma, but not to the RC hobby. Though I kinda took a LONG (30+ year) hiatus from the hobby, I actually started building RC vehicles in the early to mid '80's. My first hobby-grade kit was an original Tamiya Frog that I built in '83 or '84 when I was either 10 or 11 (don't remember exactly anymore, too long ago!). Loved flogging that thing, and soon found myself modding it with as many CRP and Parma upgrades as I could get my grubby little hands on. Then, in 1986 I built a Tamiya SuperShot, which I had a ton of fun with as well. Went on to build a Kyosho motorcycle (NSR500), a Graupner Hydroboost Speed boat, and even an RC helicopter (I think it was called a Cricket if I remember correctly?!) before eventually falling out of the hobby sometime in the early 90's when I started driving and got more into real cars (I guess people in the hobby these days call them 1:1 cars?). Just couldn't afford to do both! Heh. Aside from a short stint in the early 2000's where I got back in for a couple of years to build and run an RC Drift car and a nitro rally car with some buddies, I pretty much disappeared from the hobby until recently.

The catalyst for my return was kinda twofold. First, my 10 year old son is very much a tinkerer like I was as a kid. Likes taking apart his toys to know how they work, etc...same exact sh*t I used to do as a kid. Figured RC would be a good hobby for him, so I dusted off my old drift car from the early 2000's and gave it for him to play with. Of course, he loved it and wanted to build one of his own. He wanted to build a buggy, so, being an old-school Tamiya fan, I bought him a Tamiya TD4 Super Avante kit to build with me overseeing/teaching as he goes along (that build is currently ongoing).

The second catalyst to my return to the hobby is that, while sorting through old stuff at my parents house, I happened to come across these:

That's the remnants of my original Tamiya Frog and Tamiya SuperShot. The 2 cars that started it all for me. Finding them brought back a flood of emotion and I remembered all of the fun I had with them both as a kid. Immediately knew I wanted to get them running again. Started restoring them both (both restorations still ongoing), and in the process got bitten by the RC bug again...HARD.

So that leads me to this Kraton build. I've kinda wanted to do a monster truck build ever since about 2003 or so when I was dabbling back into the hobby to build the drift and rally car. At the time, I woulda loved to have a Traxxas Revo (the rally build was a Traxxas Nitro 4-TEC Pro with longer suspension and a bigger engine) but I fell out of the hobby again before that became a reality. Now that I was back in, a M/T build is definitely something I wanted to do. However, I had heard about the shady business practices and lawsuits of Traxxas in recent years, and wanted to stay away from their products. More interwebz digging led me to Arrma, and specifically to the Kraton 6S.

Being an old-school Tamiya fan, I thought it would be kinda cool to do a monster truck build but with a vintage Tamiya theme, and though I never owned one, I always loved the look of the old school Tamiya Sand Scorcher. Seen here:

I also saw that ProLine makes a 1/10 Baja Bug body that others have fit onto Arrma chassis....perfect. So the idea was born to build a Tamiya Sand Scorcher themed Arrma Kraton 6S. Why a Kraton 6S you might ask? After looking at the dimensions of the Proline body and comparing them to the dimensions of the different trucks from Arrma, it actually looks like the length of either the Outcast or Notorious would be better suited to the length of the Proline body. However, I want the longer wheelbase of the Kraton as opposed to the wheelie-prone Outcast or Notorious. Especially since I do plan to put a good sized motor/ESC combo in it. Also, I didn't want to buy an RTR Kraton, either. Not really a big fan of RTR kits since I feel like the build process is definitely part of the fun. The Kraton EXB roller was an option I was considering as a starting point, but then I happened to come across a listing on eBay for a used Kraton 6S V5 slider/roller that needed a bit of work (has a stripped rear differential input gear). The asking price was pretty low already, but you could also make an offer, so just for the heck of it I made a pretty low offer and to my surprise the offer was accepted! A quick Paypal payment, and a 4 day wait for shipping later, and the roller had arrived so I could see what I had gotten myself into.
So here she is, just after I unpacked it from the shipping box:

Not bad and overall pretty pleased with the purchase. Obviously, the rear wing has taken a beating and needs to be replaced, but I think it will be a great starting point for the build. Time to start going though everything, figuring out what I need to replace, and add to get the thing up and running. I have plans already, but will divulge them as things develop more...

 

[Sandracer_NL]

Gotta love the Baja Bugs

 

[EsotericRC]

Also, here's some shots of the stripped rear differential input gear after I pulled the cover...

The seller actually included a new gear still in the bag. He said that he couldn't figure out how to get it out to replace it, and was tired of messing with it so that's why he sold it.

One question for you seasoned Arrma guys (and gals!), looking at the underside of the chassis the spur gear looks awfully close to one side of the hole in the chassis. Is this how the spur gear is supposed to sit or is it supposed to be centered in that hole?

There is even some marking on the chassis so it looks like it may have fouled on it at some point. The mount and housing that hold the center diff don't look like they have any adjustment, so I assume this would have to be shimmed to move it? Or, is that how it's supposed to be?

Anyway, I do plan to run a Hobbywing Max6 ESC and 1650kv motor combo so i'll need it to be as bulletproof as I can get it. Not sure what steering servo i'm gonna run yet, but am planning on picking up both the carbon ESC mount and carbon servo mount from BasherQueen for it. Anyone have any recommendations on a good strong servo for this build that isn't insanely expensive?
I'll post more as things progress...stay tuned!

Gotta love the Baja Bugs

Yup! Love the look of the ones that i've seen on here!

 

[Sandracer_NL]

That center diff positioning seems off indeed. Looks like it’s shimmed or the wrong size bearing pushing it to one side of the spur gear slot.
As for a good and relatively cheap servo: DS3235 (pro).

 

[a2lowvw]

I think the plastic center diff mount was put on backwards.

 

[EsotericRC]

That center diff positioning seems off indeed. Looks like it’s shimmed or the wrong size bearing pushing it to one side of the spur gear slot.
As for a good and relatively cheap servo: DS3235 (pro).

That's what I figured. I mean, I have no experience with these trucks specifically, but am experienced mechanically (I'm a BMW Certified Level 1/Master Technician that owns and operates my own BMW specialist shop) and it just looked "off". Good thing i'll be disassembling the entire rig eventually and will be going through everything. Will figure out why it sits like that...

I think the plastic center diff mount was put on backwards.

Hmm, will definitely have to take a look at that. weird thing is that the plastic part of the diff housing looks to be actually barely making contact with the plastic center diff mount. Something is definitely askew. Once I pull it all apart, should be able to see why...

 

[EsotericRC]

Started a bit of exploratory disassembly today. Partially to familiarize myself with the Arrma layout, and to start diagnosing some of this chassis's "issues". Since the input drive gear of the rear differential is stripped, I started with removal of the rear gearbox and suspension assembly from the chassis:

The previous owner said that the grub screw on the drive cup to the rear differential input gear was stripped and that he was able to extract it, but for some reason he was not able to get the drive cup to separate from the input gear. Turns out, the drive cup was seized onto the input gear's shaft, but some careful "encouragement" using a small punch and a small ball peen hammer made easy work of separating them.

Inside of rear diff housing had some caked up grease mixed with dirt, debris, and metal from the input gear. Cleaned that all out with some Brake Clean and a toothbrush.

Luckily, the previous owner included a new replacement input gear, so I cleaned up the bearings and installed it.

Despite the input gear being shredded, the gear teeth on the rear differential are surprisingly fine with no visible damage to the teeth. It did have the same gunk all over it that the inside of the diff housing had so that got cleaned up with some Brake Clean as well.

Reassembled the rear diff with the rear dogbones and put the cover on, but while tightening the screws for the cover realized that the holes are stripped and won't tighten completely. Bummer. The joys of following up someone else's shoddy work. Heh. Being a professional automotive technician...nothing i'm not used to. LOL. Unfortunately, that means i'm gonna need to replace the rear gearbox case/housing.
Here's a question though for the Arrma experts...should I replace the rear gearbox case with a stock plastic one, or move to an aluminum gearbox case (ie: Hot Racing, etc)? Would an aluminum gearbox case be worth the added weight? I'd like to avoid unnecessarily fattening up this rig with heavier parts, but if there is a tangible benefit to the aluminum gearbox case over the plastic that makes it worth the weight penalty, I may be willing to make the switch to aluminum. What are your thoughts on this?

Anyway, next I moved on to looking at the center diff and figuring out why the spur gear was so off. Pulled the roll cage and center diff upper plate off and found this:

@a2lowvw was 100% right. Plastic portion of the center diff mount was installed backwards. Lovely. The center diff housing was also rubbing on the plastic mount.

Looks like i'll be replacing that piece as well. There any benefit to aluminum there as well?
Reinstalled the plastic bracket in the correct orientation and put it back together to check if everything now fit properly.

And from the bottom:

Looks much better. Heh. Anyway, that was all the time I had to work on it today. Will dig into the front end next to see what surprises lurk inside up there. Stay tuned...

 

[Sandracer_NL]

Looking good.
As for the center diff mount; I have this in the Mojave
https://nl.aliexpress.com/item/1005..._list.0.0.261c79d2tlAn7F&gatewayAdapt=glo2nld

 

[EsotericRC]

Looking good.
As for the center diff mount; I have this in the Mojave
https://nl.aliexpress.com/item/1005..._list.0.0.261c79d2tlAn7F&gatewayAdapt=glo2nld

Thanks. Was contemplating on whether the upgrade to aluminum was worth it for the center diff mount, but seeing as I am planning on running a Hobbywing Max6 ESC/1650kv motor combo, the added strength in the center differential mount would probably be ideal. Will add that to the growing list of parts to buy.

For that matter, I think it may be a good idea to spring for the aluminum gearbox cases as well to strengthen the drivetrain. The added strength there may be worth the weight penalty. I'm just thinking out loud here, but definitely interested in hearing people's thoughts on this.

 

[EsotericRC]

Did a bit more exploratory digging today, this time looking at the front end of the rig. Pulled the front diff cover to inspect the front differential.

Teeth on the front diff look good, it's just packed with a bunch of grease. That necessary on the Arrma diffs? Overall the front diff looks good other than this:

This Kraton has obviously suffered from the typical right front axle popping out...likely on full compression. Some damage to the right side diff output drive cup, and the dogbone end is pretty chewed up as well. Looks like the shaft is slightly bent as well.

On top of that, looks like when it has popped out, the end dug into the plastic of the lower arm quite a bit. So, looks like i'll need to replace the output drives (looking at the M2C ones), right CVD, and right front lower arm in addition to addressing the shaft popping out in the first place. When I get to the point that I am assembling to get this thing to run, will address the front droop setting as well possibly installing some compression limiting spacers using silicone fuel tubing. What other fixes are there for addressing the front shaft dropping out upon full compression?

Moving along, the front right upper arm seems to have quite a bit of lateral play. A closer look and it looks like one of the plastic shims is missing. Here's the pivot of the right upper arm:

And the left front one:

Left front one has a total of 3 shims. 2 thinner ones towards the rear and on thicker one at the front. The right only has one thinner one and one thicker one. I'm assuming that it should have 2 thinner ones and one thicker one. Is that how the Kraton's normally come.

One other question I have for you experienced Arrma guys and gals. This is regarding the shocks. The shocks feel fine under compression and rebound, but If I try to move the shock bodies laterally, the shocks seem to have quite a bit of lateral play where the piston rod goes into the shock body. I took a video of this but couldn't attach it. They don't leak at all from the rod seals or anything, it just seems weird that there is that lateral play. Is this normal for these shocks? I don't recall my shocks from other manufacturers having that much lateral play and don't have any other Arrma shocks to compare it to, so figured i'd ask.

Anyway, that pretty much covers going over the chassis and to see what we have and what it needs. Time to start planning out repairs and upgrades needed to get this thing up and running. Will start posting those plans soon. Stay tuned...

 

[EsotericRC]

So, my goal at this point is to replace what is damaged and needed to get the chassis to a point where it's ready to run...plus a few key upgrades that I feel are "necessary" at this point. Of course, If something needs to be replaced and there is an upgraded part available, i'll likely opt for the upgraded part instead....you know, as a kinda "while we're in there" kinda upgrade. Heh.
Based on my previous digging and assessment of the chassis, here's the list of stuff I need to address first:
- Damaged rear input shaft cup
- Damaged Center differential mount
- Damaged front differential out drive
- bent right rear dogbone
- bent right front CVD driveshaft
- bent center rear driveshaft
- damaged right front lower arm
- damaged rear differential gearbox case
- stiff steering assembly

For the input shaft cup, diff out drives and dogbones will likely opt for the stringer M2C Racing versions of these parts in addition to the M2C Front and Rear Center braces (remember those upgrades I mentioned as being "necessary" earlier?). For the stiff steering, i'm assuming that it still has the bushings that the Kraton came with originally, so I'll likely upgrade the steering to ball bearings using the Hot Racing Steering Bellcrank setup in conjunction with the BasherQueen Adjustable ServoSaver and BasherQueen Carbon Fiber Steering Kit (Top Plate, Ackerman Plate, and Steering Plates). The other stuff will get stock Arrma replacements, with the exception of the center diff mount. Will likely opt for a Hot Racing aluminum mount for that.

In addition to this stuff, the plan is to run a Hobbywing Max6/1650KV motor combo and might spring for a Reefs Raw 500HD servo. So, will likely pick up the BasherQueen Carbon Fiber ESC Plate and Servo Mount. For wheels/tires am going to run the Proline MX38 Belted Badlands. While I kinda hate that you are forced to use their wheel adapters (and likely have to upgrade to the ridiculously expensive aluminum version since the plastic ones that come with the wheels usually crack), I do LOVE that that Raid wheels that the tires come pre-mounted to are pretty much an exact copy of the Method Racing Wheels I have on my daily driver lifted Subaru Outback. Yeah, i'm stupid like that. Heh. To round it all off, I need to also pick up a Proline Baja Bug (Short Course) body to fit to my Kraton and paint, etc.

Man, looking back at this now...I think this might have snowballed into a much bigger project than I was initially anticipating and might be getting a bit out of hand. At this point, it almost might just be a better idea to buy a Kraton 1/8 EXB Roller. Heh. If the EXB was actually currently available (they look to be out of stock and backordered at the moment), I might have actually considered it...BUT, then it wouldn't be MY Kraton built just the way I wanted it. What's the fun in that?! Heh. (no offense to you EXB owners out there! It looks like a GREAT rig!)

Anyway...that's the plan thus far. Time to start buying/ordering some parts. Might need to sell off some of the rare parts i've collected over the years for 1:1 car projects, just so I can fund this Kraton build.

 

[ColosTommy]

Any updates on this?