MF-01X brittle plastic?

[one_hit 1046]

Found a few more cracked areas. This time around both front upper arm mounts. 
 

[ChrisRx718 4470]

I also bought and built mine when the 01X Jimmy was first released and my chassis isn't cracking in those places. The prop gear covers are however cracked in the same place as yours.

Mine is typically stored in a shed where it can get very cold. This last winter killed off some tyres and I'm attributing that to poor storage conditions and not treating the rubber.

Does it get very cold where you store your cars?

[Nikko85 3453]

A little worry as I've got two of these.

Could it be a bad batch of plastic (or boxes stored incorrectly during shipping or in a warehouse before sale)?

Did you use thread locker?

[one_hit 1046]

@ChrisRx718 it doesn’t get cold here at all, even with air conditioning the lowest the temperature will drop to is about 24C.  
 

@Nikko85 I did not use anything on the screws. As you can see from the photo with the motor, even the area above it with no screws is also cracking. So the problem is really the plastic itself. 

[Raman36 1656]

All M chassis plastic that has a shine to it is a kin to peanut brittle 😂

[Kowalski86 3034]

5 hours ago, Raman36 said:

All M chassis plastic that has a shine to it is a kin to peanut brittle 😂

It's supposed to be polycarbonate iirc, but to me it always felt close to the shiny ABS plastic used on other Tamiyas, just more rigid.

With the TT-02 diff covers...those really should have been made from a better plastic, the stock ones feel like bottle caps!

Theres an upgraded set for the TT02B but I dunno if it'll fit the standard chassis.

[Raman36 1656]

1 hour ago, Kowalski86 said:

It's supposed to be polycarbonate iirc, but to me it always felt close to the shiny ABS plastic used on other Tamiyas, just more rigid.

With the TT-02 diff covers...those really should have been made from a better plastic, the stock ones feel like bottle caps!

Theres an upgraded set for the TT02B but I dunno if it'll fit the standard chassis.

The diff covers crack at the screw holes frequently. Tamiya should have addressed them ages ago. 
 

The grey ones from TT02D were of better material. Spare parts tree is really hard to come by. 

[Kowalski86 3034]

19 minutes ago, Raman36 said:

The diff covers crack at the screw holes frequently. Tamiya should have addressed them ages ago. 
 

The grey ones from TT02D were of better material. Spare parts tree is really hard to come by. 

I really think the tougher diff covers and "hard" chassis should've been standard. Especially for an entry-level type kit.

[one_hit 1046]

@Kowalski86 good tip on the TT-02B reinforced diff covers, they do fit, that’s what I’m using now. Didn’t make sense for me to get the regular TT-02 A parts because the Type S only uses the diff covers, steering arms and servo mounts on those trees. And since I have the aluminum steering set and servo mount, that means I can only use the diff covers. At least with the TT-02B parts, I get to use the arms on my Neo Scorcher. 

[Juggular 4964]

Ouch, I feel you. 

I cracked my re-issued Blackfoot chassis just like that.  But I did use a big screw driver for a small screw. Too much torque.  I do suspect the plastic has gotten a bit more brittle than before because I didn't have that problem with older ORV chassis from the 80s.  

My MF01X doesn't have any crack, however. (Then again, I did not subject it to any stress. All screws are stock.) 

The problem might be machine screws.  (Below are M3 self-tapping screw and M3 machine screw. I think both are Tamiya.) 

My cheap caliper says that the shanks (the rod part) are 2.1mm vs 2.3mm.  This makes sense. Self-tapping screws have to have skinner shanks. The material dug out by the thread would deform and come out to make it fit tighter. We've all seen the plastic dust on screws. 

That's about 10% difference.  On machine screws, the threads are twice as many at given length. Since they are not supposed to dig as they go in, the shank can be fatter.  No need for extra room for dust.  So the shank is 10% fatter, the thread is twice as much in volume. Either the screws have to give, or the plastic.  Unfortunately, the plastic seems to have cracked.  

Tamiya occasionally gets some parts wrong. Most of 3 dozen kits I have are cheap bashers. But a few holes were too tight on DN-01. Fiber-reinforced plastic is tough. The screw would get too hot to touch, just from the friction of going in (I should have drilled the holes wider).  If it was the same kind of plastic as MF-01X, they would have cracked.  

While some plastic could be forgiving, I prefer to stick with the screws the engineers intended.  

 

[alvinlwh 5895]

6 minutes ago, Juggular said:

The problem might be machine screws.  (Below are M3 self-tapping screw and M3 machine screw. I think both are Tamiya.) 

Good point. I was reading the XV-01 instructions yesterday and saw this warning/instruction.

Don't think I had seen this in any other kits before and the XV uses (almost) all machine screws unlike any of my others.

[one_hit 1046]

1 hour ago, Juggular said:

Ouch, I feel you. 

I cracked my re-issued Blackfoot chassis just like that.  But I did use a big screw driver for a small screw. Too much torque.  I do suspect the plastic has gotten a bit more brittle than before because I didn't have that problem with older ORV chassis from the 80s.  

My MF01X doesn't have any crack, however. (Then again, I did not subject it to any stress. All screws are stock.) 

The problem might be machine screws.  (Below are M3 self-tapping screw and M3 machine screw. I think both are Tamiya.) 

My cheap caliper says that the shanks (the rod part) are 2.1mm vs 2.3mm.  This makes sense. Self-tapping screws have to have skinner shanks. The material dug out by the thread would deform and come out to make it fit tighter. We've all seen the plastic dust on screws. 

That's about 10% difference.  On machine screws, the threads are twice as many at given length. Since they are not supposed to dig as they go in, the shank can be fatter.  No need for extra room for dust.  So the shank is 10% fatter, the thread is twice as much in volume. Either the screws have to give, or the plastic.  Unfortunately, the plastic seems to have cracked.  

Tamiya occasionally gets some parts wrong. Most of 3 dozen kits I have are cheap bashers. But a few holes were too tight on DN-01. Fiber-reinforced plastic is tough. The screw would get too hot to touch, just from the friction of going in (I should have drilled the holes wider).  If it was the same kind of plastic as MF-01X, they would have cracked.  

While some plastic could be forgiving, I prefer to stick with the screws the engineers intended.  

 

I initially built the MF-01X with the stock self-tapping screws, and only recently replaced them with machine screws because the rear bulkhead screws kept loosening up. So while some of the cracks can be traced to the screws (such as the body post cracks) it was already starting to crack even with the stock screws. Here’s a photo from Feb 24 when I first noticed the first crack. It still had the stock screws then. Looking at the photo, I can see that the front upper arms were already cracked. I never replaced those screws since they are flanged self-tapping screws, and I never removed them before. Now the rear upper arm mounts and damper stay mounts - they are machine thread (because that’s how it came in the box and there are no self-tapping ball connectors) as well as the rear damper stay mounts (the carbon came with machine screws). Both were installed during initial assembly in 2015 and both are cracking as well.

[Saito2 6686]

1 hour ago, Juggular said:

While some plastic could be forgiving, I prefer to stick with the screws the engineers intended. 

This ^^^

 

[one_hit 1046]

@Saito2 Tamiya has a habit of specifying machine screws to replace self-tapping screws when installing hopups. Examples would be the carbon damper stays for the MF-01X, the aluminum upper arm mounts for the TT-02 Type S, and steering arm screws in the TT-02 racing steering set. So they surely think it’s okay to replace the self-tapping screws with machine screws, especially since they also sell hopup Titanium machine screw sets for kits that came with (and as you said, designed for) self-tapping screws 

[Saito2 6686]

I guess they do. Like I said, I wish I had more answers for you @one_hit, but I think between all of our suggestions here, we've covered most of the possibilities. Maybe its just defective material. I don't know.

[Juggular 4964]

For me, experimenting is half the fun.  When you get the new chassis, there is an option of using machine screws on half, self tapping screws on the other half.  If cracks develop everywhere, it must be something else. (Hopefully nothing like ozone, which is bad for health)  Cracks all over like that is relatively rare to see.  I would be careful not to overtighten. From personal experience, hearing "Crack!" while having fun building felt like dropping a baby. "Nooooo~~!!" 

Hopefully, you'd have a better luck with the new chassis (who knows, you might have gotten an extra brittle chassis before. The factory might have run out of pliable pellets or something).