Kronos XTR Horatio's XTR Build

[Horatio]

Whilst for bashers, weight isn't a huge concern for our off road rigs, there's not really any disadvantages keeping the weight down.

So I checked around and was amazed to see such a huge difference in weight between 6S rigs.

Kraton 6S rigs weigh from 5.896kg (13lb) to a hefty 8.264kg (18lb), depending on the amount of M2C upgrades.

Here's my rigs for reference. Note the brushless rigs are the weights before batteries. The weight on my Kronos includes a 38 gram gps and belted tyres.

I'll hasten to add, that the choice of tyres has a huge impact on overall weight. Whilst I selected these 'MFT' tyres because they were lighter than the Jetkos, the full set are still 228g (0.5lb) heavier than the unbelted stock tyres.

Corally claim 4.450kg before electronics for the 2022 Kronos XTR, and 4.700kg for the regular 6S Kronos before electronics.

According to Woodie, the XTR without batteries but with all electronics and stock wheels and tyres is 4.649kg (10.25lb).

Race rigs are very lightweight in comparison. The Sworkz is stupidly light, considering the weight shown here is with belted sweep tyres.

Here's a shocker though. I used to race my Savage, back when MT racing was a thing, before the first GS Storm and Truggy class came into being.

It's lighter than the modified Kronos! I wouldn't have put money on that.

 

[Horatio]

Ok, I had to do it. My 'light-weight' Baja 5B SS. 12.298kg (27.11lb). But - 2.315kg (5.1lb) of this heft is from the ridiculously heavy wheels and tyres. The remaining 9.983kg is a good weight for the chassis with this amount of alloy - upper arms, towers, clutch housing and transmission quick diff case.

 

[Horatio]

It's that time of year again, when the days start to get longer and Spring is in the air!

Blowing the dust off the Kronos Widebody......

I'd like to put this bad boy through it's paces off road and see how it does with 0° front kick.

 

[Nelson.81]

Send it

 

[Horatio]

Kronos and T2E in the boot, going out for the first outing in 2025.

Perfect weather was increasingly chilly as the sun got lower, but it was clear and dry.

Gearing was 17/46 and easily good for 60mph on the bargain basement Surpass Rocket motor.

A leisurely 0-60mph of 4.89 is full second slower than the Kronos' best time achieved with the Kuron 825. But this belies the reality that in the middle speeds, the motor provides good torque and feels punchy and useable. More importantly, running the battery down to 20% saw motor temps in the 100°F range - so it wasn't breaking a sweat, even with 2 or 3 60mph passes thrown in.

It made me chuckle that these rigs are being compared side by side. One is more or less as it comes out of the box, with Castle MMX and sensored 1515 motor. The other, home made in a garage with RTR ESC and bargain motor. Both were extremely rapid, but the Kronos had more traction with the Louise MFT tyres than the light weight T2E did on Sweep Crusher Slicks.

The agility of the Sworkz mitigated the traction issues because it was predictable and can be caught when it goes past the limit of traction.

The Kronos can be pushed very hard and is nearly as responsive as the T2E, which given the weight difference is admirable.

 

[Horatio]

Today I finished off a once over of the XTR.

The purpose of today's wrenching was to:

• Fit the Kuron 825
• Find a straight forward way to fit the Scorched Parts titanium front centre drive shaft
• Set the rig up for 0-60mph runs
• Trial some off road running with 0° kick

It must seem a retrograde step - fitting a 3000 watt motor in place of 4292 with 4200 watts, but for 0-60 mph, the Kuron was faster - no doubt about it.

It spools up quicker, plain and simply and hit 60 mph on 13/52 using Jetko tyres.

With slightly smaller Louise tyres, 140mm Vs 150mm JetKos, but using 13/46 compared with 13/52, the rollout actually works out a tad higher. 37.58mm/rev Vs 35.62mm/rev.

This should easily get me to 60mph on freshly charged Onyx packs or my Gen(S). Depending on voltages on the day, the revised setup on Louise tyres should max out at 64.34 mph.

The challenges are traction and wheelies where you find it. You need this sweet spot. You also need to be on the limit of traction without smoking your tyres or flipping over. No driver aids - no cheating - this is all about careful use of throttle.

A quick look at the 4292 size comparison to the Kuron 825.

Note the incredibly central position of the motor and dead straight drive angle. Keeping the heaviest items close to the centre helps with the polar moment of inertia. This necessitated getting the battery moved inwards as well. Moving the weight forwards also ensures less understeer.

Steering response is extremely aggressive with less caster resulting from 0° kick, so to help tame it back a little, the upper arms are in their forward position.

It will be fun trying this rig out on grass, mounds and gravel.

At some point, it would be awesome to try it out here:

It's going to be a busy Summer.

 

[Horatio]

The scorched parts titanium front centre is significantly thicker than the standard driveshaft, so you don't have the option of lifting the diff straight up and out. It bugged me how close it was to being doable.

Well the normal method of centre diff removal is 4 screws.

With the titanium front centre I can keep it to just 6 screws + 2 slackened and removing the motor.

The central 2 screws holding the motor mount allows the diff to be removed sideways from the mount - and that's okay. It's tolerable.

This front centre shaft was donated by Nelson here on the board.

It's a burly beast and is straight as an arrow, so can certainly take some serious torque. I'm hoping it quieter, smoother and thus more efficient, affording lower 0-60mph times.

I'm also hoping some Kagama LE drivers will challenge my 6S times. Or anyone for that matter!

 

[Nelson.81]

Could drop your castle motor into it be a bit more spicy. Some more bits to do to my Kronos, another delivery arrived today had it delivered to my parents I’ll pick it up later. But I’ve sliced my hand/finger pretty good so won’t be doing any wrenching anytime soon

 

[Horatio]

Could drop your castle motor into it be a bit more spicy. Some more bits to do to my Kronos, another delivery arrived today had it delivered to my parents I’ll pick it up later. But I’ve sliced my hand/finger pretty good so won’t be doing any wrenching anytime soon

I tried doing two emojis for the price of one. Like the suggestion of the castle, dislike the fact that you have sustained a hand injury.

Super glue works well for a quick patch up.

 

[Nelson.81]

Cheers It’s mainly my thumb causing me issue worst spot ffs can’t do nothing without cursing at it. Sliced it open good the knife had been blunt and day before I sharpened it perfect timing

 

[Horatio]

Cheers It’s mainly my thumb causing me issue worst spot ffs can’t do nothing without cursing at it. Sliced it open good the knife had been blunt and day before I sharpened it perfect timing

View attachment 9316

That must sting like a MF!

Deffo patch it up with Cyanoacrylate (vetinarian glue) once you've cleaned it. It should hold and stop it from anything getting in while you work.

 

[Nelson.81]

yes it’s a bit tender it’s healed a bit done it last Thurs wearing plasters a pain in the A$$ but if don’t wear one & catch it on something cutting a dam onion & I don’t even like onions

 

[Horatio]

yes it’s a bit tender it’s healed a bit done it last Thurs wearing plasters a pain in the A$$ but if don’t wear one & catch it on something cutting a dam onion & I don’t even like onions

Bloody onions! Vicious little £¥€&£R$. I like them when they're fried in butter and nicely caramelised though!

Or in a good Chilli.

 

[Horatio]

So, centre diff rebuild will begin in my new and improved workshop (with over double the bench space and extra lighting!!).

Peg boards are being investigated and I have a couple of decent ideas for the walls behind each bench.

EVR very kindly sent his centre diff and mount, all from 7075 complete with a pair of decent looking bearings!

Many thanks to Nelson for putting in a word for me (EVR stuff is only available through FB - which I don't use).

It wouldn't have been possible to order these excellent upgrades without Nelson's input. Thank you!

I'll put the diff together today with a thicker centre oil and post the pictures here as the job gets done.

 

[Nelson.81]

Nice, diff mount insert abit of a tight fit but you shouldn’t see anymore diff leaks with his diff case.

 

[Horatio]

The joy of a revised, central drive line and different centre drive shafts - this technique for getting the diff out.

My diff had been leaking again - let's find out why...

I've seen worse leaks, but clearly the leak is coming out of just the spur side - at the output.

As the rig gets some use, it turns out another 0.2 shim was required under this output, to reduce end float.

However, the leak in this instance was down to this:

Spot the missing chunks! Green slime will fix it for now. 10 of these are on their way - I couldn't find any o-rings of this size in my spares.

Removal of gears can be tricky due to stiction.

No additional shims required, however I used green slime to help with any leaky issues.

Diff gears dropped in - zero issues. Very impressed with the precision. No additional shims required!

Did I mention green slime? More green slime.

Leaky diff? Green slime. Leaky shock shaft? Green slime. Running out of money? Green slime. STD? Green slime...... You get the picture.

Yes - the bearings are very close - as they should be, so use a little copper grease and thank me later.

A smear of copper grease is no bad thing anyway when fitting steel into aluminium alloy. You can take my word for it, or you can Google it. I use copper grease on all my rigs since the MBX4RR.

This is one sexy looking assembly. Love the little cooling fins on the one piece diff. Less places to leak from!

Trial fitting the spur guard. As the EVR part is not split, the screws going down into the 7075 alloy are not 4 inches long like on the stock arrangement. This is a good thing - but you need to supply your own button head screws.

Look at it!!! It's beautiful!! And machined with excellent concentricity and very fine tolerances. Ahem.......Unlike my chassis, that was fashioned using a hammer and a cordless driver.

But we're getting there - opened up a hole a little here and there on the chassis to comply with the gods of EVR.....

Front end service. I noticed some slop on the input into the front transmission - so let's get it right...

Input pinion required tlc - a clean, and an extra 0.2 shim to pull it closer to the crown.

Hudy Graphite grease applied for some lasting low mess lube.

 

[Horatio]

Fresh blue threadlock on input shaft grub screw....

More to follow - the rig is getting fettled to make the most of these new precision parts and to do them justice.

It's very clear they are machined to very fine tolerances - certainly higher than the mass produced stock parts. This is why you need them on your drive train - right?

Erik Van Ravenstein will hopefully check out this forum and keep his ear to the ground. I have nothing but praise for the speed at which my parts arrived and the fabulous quality of the machining.

Cheers to Nelson for making contact with EVR

Any how, watch this space!! More to follow.

 

[Horatio]

I nabbed the last 2 packs of these from Modelsport, but they're usually in stock. Well worth keeping them healthy, with lashings of green slime for good measure.

 

[Horatio]

Nice, diff mount insert abit of a tight fit but you shouldn’t see anymore diff leaks with his diff case.

I like the 1 piece design. There's less places for it to leak, that's for sure.

It seems my TC diff really ever leaks from one place - assuming my spur gear stays where it's supposed to be!

The O-ring in that spur has a lot to do. As it wears, the inevitable leaking occurs through that back bearing.

I noticed some backlash here, so shimmed it accordingly for the new diff build. However, green slime should help until new o rings are fitted.

Copper grease really helps with the bearing housings. It's good practice anyway with steel in alloy, especially when it's an interference fit.

It's a good opportunity to give the front transmission a good tear down. I've been wanting to do it for a while and use M4 x 22 and M4 x 20 screws to secure the front gearbox. They needed to be longer to make up for the thicker chassis.

The front input gear and crown was just starting to get sloppy. Intervention here prevented a stripped set of gears for sure.

Can't wait to get it all back together tomorrow morning and ready for a shake down.

 

[Nelson.81]

Love it I see you got his newer style diff case with cooling ribs, he started doing black anodising on some parts too. When I had leaking diffs I went looking for better oring & couldn’t find that size anywhere except from corally. I compared new to old thought the service items looked thicker but neway. Also used bit of copper grease installing mine great minds think alike. My front drive up loose too so gonna have to pull it apart see what’s up. I’ll drop EVR a few pics of your build , thought about mentioning it to him about joining forum here, as he likes to work in the shadows not give out his details would make it easier for people on here to connect with him but his choice at end day.