JRXT rediscovery and rebuild (lots of pics)

[modifieda4]

As found in my parent's attic, my JRXT I bought new with HS summer job money in '89 or '90. I did not use it much before other priorities kicked in. Since then a lot has changed, including acquiring 20+ years of experience as a mechanical engineer. I've decided to take on this as rebuild/refurb project.

My JRXT after long term storage at my parents + one recent winter outside under a tarp:


I did not take alot of pics before tearing into it. Here is me measuring to see if modern batteries will fit (more on that later):


the motor:


the rear end off the car:



the front end off the car:


the weird losi RC10 steering bellcranks:


obviously there is alot wrong with the car. From the RC10 bellcranks, rusty and dirty parts, and misbuilt items and misfit parts...though there is some good news:

• the diff appears to be functioning

• the chassis is scratch free

• 3/4 shocks appear to have not leaked and the suspension articulates fine

the goal is to tear it down completely, wash and clean everything, and bring it up to working/original condition. in the end it will be fully functional and along the way i can spend some time with my kids during the rebuild.

[modifieda4]

real life car maintenance experience kicks in here. rusty ball ends:


using POR-15 metal prep. (zinc phosphate solution) It attacks the rust and adds a rust preventative conversion coating to steel:


after 1-2hours in solution:



(do not leave parts in longer, crystals start to grow on the surface of the parts)

all salvageable steel parts will go through the treatment. The parts come out gray and lose their black oxide coating. personally i don't care about that.

here is the losi wrench, and the turnbuckles after treatment:

[Lavigna]

Great start to your build! It's great you still have the truck. I did the same thing to my original RC10T a few years back. I have a build thread on it in the truck section if you want to take a look.

That treatment on the metal parts looks to work great. I need to look into this for myself. If you put in the time and effort, you can have that truck looking better than new, and with minimal parts replacement. I just rebuilt a JRXT that looked about the same, and now it looks like this (below).

I look forward to seeing your build. Thanks for sharing.

[modifieda4]

Great start to your build! It's great you still have the truck. I did the same thing to my original RC10T a few years back. I have a build thread on it in the truck section if you want to take a look.

That treatment on the metal parts looks to work great. I need to look into this for myself. If you put in the time and effort, you can have that truck looking better than new, and with minimal parts replacement. I just rebuilt a JRXT that looked about the same, and now it looks like this (below).

I look forward to seeing your build. Thanks for sharing.

Hey thanks alot for comments! Your truck looks really good, I don;t think i'll be able to get to that level of cleanliness.

I'm getting a little carried away with upgrades, i might have enough parts left over for another jrxt. lol.

[modifieda4]

some more progress:

shocks as they were:


disaaembled and cleaned up, like i mentioned before only 1 had leaked in 30years. wow. I bought 4 new double oring cartridges anyway (i also broke a shock collar sanding the gap to make them clamp again):


here is the rear suspension cleaned up and reassembled:


and here is the front. i've used graphite in all the moving joints. without the shocks in everything moves with very little friction:

[modifieda4]

It was clear that I had drilled out the steering post holes in the chassis to make the RC10 steering bellcranks work. The smaller stock screws didn't fit well. So here is my attempt at righting the wrong, since the chassis is basically flawless except for the holes:

holes masked:


JB weld mixed with about 40% Silicon Carbide powder. I hope this adds enough compressive strength to not move once screws are bearing down on it. Also I hope to prevent cure shrinkage of the epoxy:



holes filled:


top side cured with masking removed:


bottom side cured:


so now the holes are filled. I think it turned out about as good as expected. the next step will be to drill them to the right diameter and c'sink the bottom. I'm worried that getting through the silicon carbide with drill bits. i might use a few

[klavy69]

I'm worried that getting through the silicon carbide with drill bits. i might use a few

don't worry about sacrificing drill bits...worry about trying to drill through something harder than the surrounding surface. Easily a drill bit will walk off of the harder surface sink in the softer surface quickly.

It does look good though. Surely the chassis was worth it since it does look pretty nice. Good luck and will be checking back to see progress pix

Todd

[modifieda4]

I'm worried that getting through the silicon carbide with drill bits. i might use a few

don't worry about sacrificing drill bits...worry about trying to drill through something harder than the surrounding surface. Easily a drill bit will walk off of the harder surface sink in the softer surface quickly.

It does look good though. Surely the chassis was worth it since it does look pretty nice. Good luck and will be checking back to see progress pix

Todd

good points! i'll make sure to get a good pilot hole going before drilling to size.

[Lavigna]

Great build so far. It's too late now that you have filled the holes, but I have seen people who had the same issue use smaller bearings to accommodate the original steering setup. I looked for the thread but couldn't find it. I think it's cool how you filled the holes.

I will definitely be following your build. Keep it up!

[modifieda4]

while waiting for parts i decided to make progress on the electrical front. time to get rid of the connectors:


i decided to standardize on XT-60 connectors since the battery packs came with them and for the performance. I wired two more caps on the power input side.



the esc pictured is a Hobbywing 1060 ESC.

[modifieda4]

I went with NiMH batteries since they are the closest form factor to NiCd. Based on posts here and elsewhere I expected them to be too big to fit in the JRXT battery spot. This is true

The pack is too tall for the rear bulkhead by a hair and too long in the front where the wires exit the end cap.

by removing the end caps the battery fits fine. of course now there are exposed electrical contacts.

here is the battery sans endcaps, with electrical tape covering the contacts and with heat shrink ready for heat:


add heat:


now in comparison to an unmodified pack. you can see now much shorter it is without endcaps. it fits fine now:


what is not shown is that i added a strain relief by taping the battery leads back against the battery. i dont want the solder joints seeing flexing.

[modifieda4]

i had to clean up the motor given its state. i desoldered all the caps etc and took it apart to check the insides.


here is an exploded view of an MTM motor:


everything looks pretty clean inside, i don't think i'm going to touch anything even though the commutator is not all shiny. thoughts?

[modifieda4]

another baby step. holes marked for through drilling:


starting to drill the first pilot hole:


the first bits through did wander, going slow helped. no real issue actually cutting the glue SiC mix.

intermediate drill size:


final size, 1/8":


visually things look slightly off center, but the actual amount is too small to have any impact. (the best i could do with hand drilling)

now i need to get a 82deg c'sink bit to do the other side.

[modifieda4]

ok, the body repair is complete, i c'sinked the holes so the screws are flush with the body, i think it turned out well.

bottom with hole repair complete:


top: there is barely any epoxy showing..


screws and posts in, all torqued up:


top view with posts:


the epoxy seems rock hard, no issues torquing up the bolts. i think i would recommend this method for any hole repair on a chassis. final thoughts will have to wait until the JRXT is up and running

[jwscab]

Where the heck did you get silicon carbide powder? Good idea though, some kind of strong filler helps support the epoxy.