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How to deal with KS18XL cracked inner shell

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Hello brain trust. I need help/advice on an issue. My KS18XL's inner shell was badly cracked at the pedal hanger attach points. Very badly. So I ordered a new shell from Jason at eWheels. The white one, which is less brittle. I even have a thread going on about the disassembly and reassembly. Well, today I finished assembling onto the new shell, and something happened: I was very careful not to over-torque the attachment bolts, and I used plastic washers to spread the load.  Everything was looking good:

20200504-020442960-i-OS.jpg

However, at the very end, as I was putting on the side panels they weren't fitting right, so I pushed a little harder than I should have to try to align screw holes. In the end I took the covers off again because something was clearly wrong (one corner of the cover was sticking up even after forcing on the screws. Well, the left inner shell is cracked again, at the pedal hanger attach area. The cracks (a big one on one side, and a smaller one on the other side) seem to have happened due to flexing of the shell when I was pushing to try to get the cover on. Here's what it looks like now:

20200504-034256125-i-OS.jpg

You can't see the crack on the other side, (the smaller one, but as you can see this one is quite long and causes that side of the shell half to be less stiff. I can assume this crack will widen and lengthen over time, and eventually I'll have another useless shell.

I know the reason the cover didn't fit by the way, and it has to do with a change in the shell design from my old black shell to the new white shell. The metal tabs that hold the trolley handle bars in place used to be attached with plastic spacers:

20200504-035323172-i-OS.jpg

See the little white washers? Well, when they're on, this is what it looks like on the new shell:

20200504-041323144-i-OS.jpg

I didn't notice until too late that this makes the tab be too high (it's not even touching the rod), and it also makes the screws stick up too high an interfere with the side panel.  Dangit!  I've fixed this, but the damage to the new shell is done. I blame myself for a) not noticing this small design change, and b) being too "enthusiastic" at trying to get the covers on, instead of doing some troubleshooting to see what was causing the problem.

So, what to do? Order another shell and do this all over again, or is there a worthwhile repair? For example, will a two-part epoxy compound do anything here? I'll sit here and fume while I wait for responses :( :furious:.

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Posted (edited)

Plastic weld it. Use an old soldering iron and youtube.  You can also 'weld'  wire mesh INTO the repair joint (old window screen works good).  If you plan on it lasting forever, you may want to use a fiberglass mesh over that with the epoxy(dont try to weld fiberglass matting, use it with the epoxy). DOn't order another shell yet. The white plastic seems to have less graphite in it and wont turn to dust so easily(Both my 18's are white for THIS reason!). Lookup diy plastic welding. Youll learn something useful for many things and you already have a test subject. If you want to get REALLY technical, you can look for plastic codes on the parts and order fill rod that is compatible, and bevel, weld/fill. I dont think you'll need bother, but it wont hurt to look around for some similar plastic scrap around the house, in case you need it. Over the weld,  use a flexible epoxy or  the epoxy will crack right back. I keep a tube of this on hand and use it all the time. It can be found at auto parts stores and its white. Dries REALLY fast when you mix it up right. Just be sure to weld first and rough up the plastic with some 100 grit or so. You'd be amazed at how many repairs Ive successfully made in the auto industry with a 'plastic welder' and 3m band products. When working under dashes of 20 yr old plastic, this kind of thing can save 1000's of dollars. DO NOT try to use superglue or bondo or fiberglass resin epoxy or any of the other nonflexible adheisives. Using nonflexible epoxies on flexing parts, only shows ignorance. If you arent overly worried, skip the welding and just lay a TON of this adhesive over it and move on. Hell, with enough quality 'glue' of the right kind, it may outlast the damn motor. Of course, once you 'glue' it, you'll play hell to remove the 'glue' and weld it later. Your call, but hell, just 'glue' it without taking it back apart... could be the level of commitment you want to take. It aint like you cant buy ANOTHER damn side later if it fails to hold. Up to you, but looking at it closely, I may just opt to glue the piss out of it, drink a beer and forget it ever happened.

*fwiw, when i installed my upgraded trolley for the 18L, I noticed it came with spacers. Maybe not, but i do recall pondering on how many spacers went there and should i use any. Now you got me wondering If i broke mine and dont even know it. I'll be opening it soon to check the trolley and replace the crap screws in the shell anyhow. Thanks for sharing this and admitting you messed up. You answered something i had wondered myself.

Structural Adhesive Kit

Edited by ShanesPlanet

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34 minutes ago, ShanesPlanet said:

Plastic weld it. Use an old soldering iron and youtube.  You can also 'weld'  wire mesh INTO the repair joint (old window screen works good).  If you plan on it lasting forever, you may want to use a fiberglass mesh over that with the epoxy(dont try to weld fiberglass matting, use it with the epoxy). DOn't order another shell yet. The white plastic seems to have less graphite in it and wont turn to dust so easily(Both my 18's are white for THIS reason!). Lookup diy plastic welding. Youll learn something useful for many things and you already have a test subject. If you want to get REALLY technical, you can look for plastic codes on the parts and order fill rod that is compatible, and bevel, weld/fill. I dont think you'll need bother, but it wont hurt to look around for some similar plastic scrap around the house, in case you need it. Over the weld,  use a flexible epoxy or  the epoxy will crack right back. I keep a tube of this on hand and use it all the time. It can be found at auto parts stores and its white. Dries REALLY fast when you mix it up right. Just be sure to weld first and rough up the plastic with some 100 grit or so. You'd be amazed at how many repairs Ive successfully made in the auto industry with a 'plastic welder' and 3m band products. When working under dashes of 20 yr old plastic, this kind of thing can save 1000's of dollars. DO NOT try to use superglue or bondo or fiberglass resin epoxy or any of the other nonflexible adheisives. Using nonflexible epoxies on flexing parts, only shows ignorance.

*fwiw, when i installed my upgraded trolley for the 18L, I noticed it came with spacers. Maybe not, but i do recall pondering on how many spacers went there and should i use any. Now you got me wondering If i broke mine and dont even know it. I'll be opening it soon to check the trolley and replace the crap screws in the shell anyhow. Thanks for sharing this and admitting you messed up. You answered something i had wondered myself.

Structural Adhesive Kit

Thanks for the advice, @ShanesPlanet. I did look up plastic welding, including the kind done with an old soldering iron and scrap plastic (vs. a gun with stick in it). One thing that's not clear to me is what type of plastic the shell is made of.  Looks like generic ABS, but who knows.  I have a couple of old project boxes that are made of a plastic that at least feels similar. So what you're saying, I think, is that I would plastic-weld along the cracks with a soldering iron, possibly adding some plastic from available scrap, and also optionally melting some wire mesh into the weld. Then, on top of that, I would optionally further reinforce by sanding/roughening and adding a flexible epoxy (optionally with fiberglass mesh), not as a repair of the already-repaired crack, but as a way to further strengthen the area. Did I get that right? Is the 3M adhesive (08101) you showed in your post a good "flexible epoxy" option to consider?

Any repair would have two constraints: the cracking is near and around screw holes, and on the outer surface I need to be able to drive screws into that area without interference from any "bulging" areas where the repairs are; also, on the inner surface, the plastic slides like a sleeve over the metal hanger, so any repair attempted on that side would need to be perfectly flush with the surrounding plastic.

Well, I guess it's worth a try. I'm going to the garage to see if I have a flat tip for my soldering iron (the normal tip on it is very pointy, for the type of electronics soldering I normally do).

I'll wait for some more replies, if any. Much too late in the evening to try to do anything right now, anyway. I wonder if riding the wheel will aggravate the damage, meanwhile.

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Posted (edited)

Yes, the adhesive i show is flexible. It is my goto and if you are careful with the tubes (its kinda pricey at auto zone) it will last years and many projects. 2 part adhesives typically dont dry out on the shelf.  The plastic shell SHOULD have a plastic code on it. Tbh, i wouldnt bother with specifics, and it is a type of 'abs''. There is so many blends of plastic, its retarded. Just find something similar(plastic bucket perhaps? No worry about uv compatibility on this one and you aint using much as theres virtually nothing to fill), would be my suggest. This plastic seems the type that should melt fairly well, just be sure to mix the fill plastic in it well and dont burn thru. Lick your finger to keep it slick and cool when forming/pressing the weld, after removing the heat. Its not a visible spot, so your learning curve wont matter much. Its just melting shit together and mixing it before it cools. I have a welder that adjusts temps for various plastics, with tips(hollow/flat/thin etc) and types of rods, but i did that stuff a LOT. 80% of the time, I used a simple flat looking shoe and some 'fiberweld' material they sold in sticks. Fiberweld was nice and worked with mesh well, but plastic rods will work too, just use 3m on top of it. The 3m adhesive  is what will hold the bulk of the stress. The plastic weld will hopefully just hold the lineup. Combined, it may outlast the damn batteries. OR, it may not and youll know better and be out another half shell. BUT, youll still have 2 tubes of badass white glue!   I am pretty sure we are on the same page, as your response sounded right. Know this, if it seems confusing, drink more. Its melted plastic and glue, with some reinforced mesh. Glob that shit on there and move on. Eventually I'll break something and itll be my turn. I hear the screw standoffs are common. No worries, Ive already got a tube of adhesive just waiting. 3m makes good shit. There's a reason it aint cheap, and neither is the value of your time! Just repeating this, reminds me to tell Jason I want a WHITE sks18, as i dont trust the black nor like rubber coatings much.

Edited by ShanesPlanet

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Update:

First, @Jason McNeil at eWheels has told me via e-mail that the incidence of cracking of this sort on the new white shells is extremely low, and he considers this a defect, so he has shipped me a new shell half free of charge. I don't relish disassembling everything again, and prying the two shell halves apart, but I will do it. Things will go faster this time, since I won't be documenting with photos as I go this time, and because I have recent experience to help me move things along. Next weekend, I guess!

Second, I do still intend to try the repairs as discussed above, but what I'll do is replace the shell half with the new one, and once the cracked shell half has been liberated from the wheel, I will attempt the repairs on it. It will be easier to work with as a single shell half that's off the wheel (easier to get at both sides of the plastic), and if I make a complete mess of the work I can throw away the piece and pretend it never happened.  If I succeed and have what looks like a strong repair, I'll have a "spare" shell half for the future, just in case.

I will report back here about the repair attempt, with some photos, to document for anyone who's curious and for any future forum searchers who're looking for this type of information.

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Posted (edited)

Hooray for Jason at e-wheels. Replace is always better than repair, IF the same quality of parts (or better) is available. Aside from the hiccups, it seems like mostly good news! At the very least, you can save a piece off the old case (less new anyhow) and keep it for future plastic weld attempts. I'd still use this as an excuse to buy some BADASS GLUE. lol    Im a broken record I know. So, how long until you decide to become an authorized repair center? Sounds like you're getting some experience fast!

Edited by ShanesPlanet

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I'll never have enough experience to be good at it, but this will be a learning experience for sure, and I'll enjoy it. I did order that 3M epoxy, and some wire mesh. I already have fiberglass mesh and a soldering iron, and an old project box made of a beige plastic that feels about right in terms of plastic type. Should have everything by early next week to make the repair attempt, and by then I should also have the shell half available to work on, as I expect to do the re-rebuild of the wheel later this week.

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Closing the loop on the rebuild (not on the repair attempt):  In the end I took apart and assembled the wheel 3 times, using a total of 6 shell halves, 4 of which I paid for and 2 of which were generously provided for free by Jason at eWheels.

The second build went well, and I was very gentle and careful.  I avoided the pitfall with those plastic spacer washers, used a lot less silicone sealant when "gluing" the two shell halves together, and applied a lot less thread-locker to the pedal hanger bolts, to avoid getting thread-locker all over the place as had happened on the first rebuild. I snugged the bolts on oh-so-gently, intentionally using just three fingers (thumb, index, middle) to hold the screwdriver, so I wouldn't be able to apply too much torque.  Thread-locker was applied to the 4 screws that hold down the mainboard (they go into nuts that are embedded into plastic slots in the shell), and to the 12 bolts that hold the shell to the pedal hangers, as before.  I avoided using the washers this time, to eliminate one possible source of "unexpected stress" on the plastic.  So, I snugged down one side (looking good), went to the other side, snugged it down as well (also looking good), and proceeded to reinstall the battery and run, connect, zip-tie, and secure the battery and motor cabling on that side.  When I finished, as I was about to flip the wheel over to do the battery pack on the other side, I noticed something:

20200509-052551688-i-OS.jpg

Faint blue lines had appeared near the bolt heads.  They were not there a few minutes earlier.  I took a photo and flipped over the wheel, to see this:

20200509-052710510-i-OS.jpg

No!  Cracking!  I had applied almost no force when putting on the bolts!  More importantly, though, why was there blue thread-locker visible in all the cracks?  I had put very little of the stuff on the threads of each bolt, but it's hard not to touch the plastic with it as the bolt is inserted, since the bolt has to go through the hole in the plastic to get to the pedal hanger thread underneath.  Btw, the first side with the barely visible lines that I showed you above got worse over the next half hour, until visible cracks appeared there as well.  What's more, one of the plastic slots where the mainboard screw-down nuts insert into had also cracked apart, I noted, and there was also blue thread-locker visible all along the break.

Jason talked to KS about it, and they believe that the thread-locker is having a very bad effect on the plastic.  It seems to me that what's happening is that the stuff is drawn into pre-existing (and normal) micro-fractures in the plastic through capillary action, where it immediately acts like acid to eat away at the plastic, widening the fractures into cracks, which allows the stuff to be drawn deeper into the plastic and continue the damage...until the liquid finally dries or "runs out."

So, thread-locker is the enemy of the plastic used in these KS18XL inner shells.  It should never come anywhere near these shells.  On my 3rd re-build, I used the washers again, and not a drop of thread-locker, and that build was successful (so far).  No cracks!  I will start a separate thread with appropriate title, as a PSA for future reference, so this doesn't happen to anyone else.

I now have two complete white shells, both with a blue mess of cracked plastic around the pedal hangers, one of them also with some cracking around where the mainboard attaches.  Haven't made a repair attempt yet, but I have plenty of plastic to work with, to see if I can build myself one workable spare inner shell "just in case." When I get around to it, I'll post here as promised with the result of that work.

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Posted (edited)

Wow, I have never heard of such a thing. I JUST had mine apart to swap a  tire around and I'm pretty sure I used blue loctite on the shell bolts. I guess I'll open it back up and check, as it should be apparent if I have just cost myself a pair of shells and a ton of work as well. I wouldnt advise of loctite on any screws that go into those brass inserts. My reason of thinking is that they are merely held by plastic. Maybe no big deal. Hell, I would have never guessed loctite, as I've been using it for decades. Thanks for the update, I'm glad you eventually got it repaired!  I had to open mine and check. I got lucky, it didnt seem to wick into the plastic. Of note, my washers are little star washers, not big like yours were. No need for loctite on mine but you can see I added it out of habit. Again, thanks for telling us, I am always ready to learn something about the methods I conduct repair. Basically, *read the fine print*

https://www.chiefdelphi.com/t/pic-warning-about-loctite-touching-abs-or-polycarbonate/134228/10

*Go figure. It plainly says on my bottle.. Avoid contact with thermoplastics... Decades of never reading the fine print... It seems loctite makes some FOR plastic tho.

 

DSCN7905.JPG

Edited by ShanesPlanet

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I guess I should've read the fine print, too.  My recent research has revealed to me that Loc-Tite is generally not safe for contact with plastics, as even if the result isn't as dramatic as it has been for me and these KS shells, it will apparently degrade just about any plastic over time.

Lesson learned.  I'm really good (and getting reasonably fast) at taking apart and putting together a wheel from parts, though.  I've acquired a skill!

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It's hard to see in the photo you added in your edit, @ShanesPlanet (kinda dark), but I think I see the tell-tale staining and maybe a crack or two?  Not nearly as bad as what I had, though.

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Posted (edited)
13 minutes ago, svenomous said:

It's hard to see in the photo you added in your edit, @ShanesPlanet (kinda dark), but I think I see the tell-tale staining and maybe a crack or two?  Not nearly as bad as what I had, though.

No cracks, i also inspected inside where the bolt goes thru the hole. Ingress would have been pretty apparent. Mines not loctite brand, but it has the warning in fine print too. Mines seems unscathed. If it becomes a problem over time, theres nothing I can do about it at this point. I'd imagine that lower quality plastics are more at risk. I'll just add this tidbit to the fading memory banks of mine and hope it averts disaster in the future. Again, thank you so much. Obviously this is something commonly overlooked, as I've been around MANY techs over MANY years and am just now learning of this. Just goes to show, length of time and/or age, is not a direct indication of a man's knowledge...

Edited by ShanesPlanet

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As promised, I'm reporting back on my plastic repair work. I had brand new shell halves to rebuild the wheel after the first two failed attempts with the Loc-Tite (thread-locker), but with 4 broken shell halves to play with, and after getting all the advice above about the potential for repair via plastic welding, I wanted to give it a try and possibly end up with a spare set of inner shell halves to use.

Out of 4 halves available, I chose the 2 that had the least amount of missing material. I scavenged some plastic from one of the remaining halves, to use as raw material for the repair. Attached a wedge tip to the soldering iron, grabbed some wire mesh to use to enhance structural strength in the most vulnerable areas, and got to work.

I was being careful with the soldering iron temperature setting, for fear of melting the plastic too fast, but in the end I found that the best setting was maximum (800 degrees F), and to just be very careful with pressure and contact time.

Tip: unless you don't like your lungs, ventilate, ventilate, ventilate! After choking on fumes for a while and blowing at the smoke to keep it from wafting into my face, I got smart and a) opened the window behind me, and b) turned on the ceiling fan above me.

The damage seen in the posts above is actually pretty mild, and it was only the initial damage.  Upon disassembly, the plastic around the pedal hanger bolts was so brittle that parts of it cracked right off.  So, in addition to dozens of cracks, I also had missing material rebuild.

I didn't document every stage/action, but essentially I ran the iron slowly over each crack, letting it sink about a millimeter into the plastic, to fuse the cracks back together, and melted some filler plastic over each "groove" to fill it in. Here's an picture of an early stage, where I was starting to apply the metal mesh:

20200601-072831997-i-OS.jpg

I will stipulate to the fact that the result is ugly. Very ugly. The iron carbonizes plastic and mixes the carbonization into the work, making it look dark and dirty. On top of that, I'm no artist, and I'm no expert, so no points for esthetics.  However, what matters is function and structural integrity, right? What you can't see here (I forgot to take a "before" photo) is that one whole corner of the repair (bottom left corner of the photo as oriented here) involved rebuilding the structure, which was missing. Basically, all the plastic from that screw hole to the nearest corner was missing and had to be rebuilt from melted plastic. The mesh needs to be melted into the plastic, to just below the surface, and acts like rebar would in concrete, adding strength.  In the photo I had just started to position the mesh on one side and melt it into place.

Tip: watch that iron. While you're concentrating on what the tip is happily melting, what might the similarly hot barrel be touching (and melting)? It would be a shame to repair the pedal hanger area, only to accidentally destroy a screw post next to it! I didn't cause any major damage, but I found repeatedly that I had "nicked" bits of plastic I had not intended to heat.

After finishing the top of each repair, I flipped over the shell half and repeated the work on the other side. Some of it looked good, but there were cracks and some gaps (missing material) on the other side, too.  I didn't apply any mesh on the underside, as there's more of a clearance problem: the pedal hanger has to be able to slide in.

Below, finally, are photos of the final result. I didn't document the repairs I made to the mainboard attachment slots, which were also damaged. The main trick with these was that they're small and tight, so it's hard to manipulate the iron and shape the plastic so that the nuts and screws will fit, and so the slots still sit flush with the mainboard. One of the four slots was half gone, so I had to rebuild it. I don't know how well they will work, but they look OK to me. As for the pedal hanger areas, they seem flexible and strong. I flexed the areas, tapped them, and bent them as much as I dared, and the plastic seemed supple and strong enough. We'll see what happens if I ever have to actually use these. I elected not to apply additional repair compound (the 3M stuff @ShanesPlanet recommended). The result is mega ugly, but it feels strong.  If I ever use the repaired halves, I might report back on the results.

20200602-020526360-i-OS.jpg

20200602-020545324-i-OS.jpg

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