MF-01X brittle plastic?

[one_hit 1046]

Decided to do some work on my MF-01X when I noticed the cracks all over. Anyone else experience the same? I bought and built this in 2015 so it’s turning 8 this year but I haven’t experienced this in my CC-01, CR-01, M03 and TT-01 which are all much older (all built on or before 2010). Needless to say, being a monocoque design I’m not looking forward to replacing the chassis on this one!

 

 

[Kowalski86 3034]

I know your pain, going through the same on a Monster Beetle (admittedly it's much older).

I've had two -01Xs and neither of them had any cracks, one even saw quite a bit of off-road action and only had scuffs to show for it.

All of mine used the kit screws, I noticed that yours has hex heads which might have contributed if they were over tightened (though that doesn't explain the crack in that part over the motor).

What kind of terrain/use did yours see?

[one_hit 1046]

@Kowalski86

I built this in 2015, use it a couple of times at the track which is indoor asphalt, then sat on the shelf until this year. Only used a couple of times this year, once on the street and a couple of times at the track so it hasn’t seen much use really. Haven’t had any crashes or broke anything yet and I’m very careful not to over-tighten the screws. I’m also experiencing the same brittle plastic problem right now on my TA02 from 1997 (which is already on replacement gear cases) and Stadium Thunder from 1998 which has cracking original red bulkheads/gearbox case). Those two are not even being used, just disintegrating by themselves while sitting on the shelf

[Kowalski86 3034]

32 minutes ago, one_hit said:

@Kowalski86

I’m also experiencing the same brittle plastic problem right now on my TA02 from 1997 (which is already on replacement gear cases) and Stadium Thunder from 1998 which has cracking original red bulkheads/gearbox case). Those two are not even being used, just disintegrating by themselves while sitting on the shelf

Those TA02s are old enough where I'd expect the plastics to get brittle, even just sitting on a shelf the plastic will dry up and crack in time.

Unless if the MF-01X sat in the sun for a while I can't explain the cracks, other than Tamiya choosing the wrong plastics for the application.

[Saito2 6686]

I'm curious if those grey plastics are ABS or PC. PC seems to be slightly superior in my experience, but neither last forever or can be rehydrated like PA plastics. Are those hex screws machine thread or self tapping like the originals? If they are machine thread, was a thread forming tap used before they were inserted (regardless of how tight they were made upon final tightening)? Tamiya molds most of their holes with clearance for their self tapping fasteners in mind. Most fractures (even using proper style fasteners) come from initial insertion. The screw enters the hole cutting threads but also creating outward pressure and usually results in micro fractures. Impact from simply driving the vehicle plus plasticizer migration over time, spread these small fissures until one day, visible cracks appear. ABS gains strength through mass and looking at most of the offending areas, there isn't a lot of material around the screw insertion points. I heat every self tapping screw I install to relieve tension (and hopefully eliminate these tiny initial fissures) and extend part life. You still have to contend with plastic's aging however, but 8 years isn't all that long unless it sat out in the sun all those years.

[one_hit 1046]

@Saito2

I still have the sprues, it says the grey chassis parts are made of PC. I don’t think the screws are the problem because even the plastic where the rear upper arms and damper stay mount into are also cracked

[Saito2 6686]

So, other than the crack above the motor, they are all cracks around screws though?

[one_hit 1046]

The covers for the propeller shaft gears are also cracked. They’re on the screw areas but the screws just slide into those parts and don’t thread into them

[Kowalski86 3034]

Did you use threadlock by any chance? Some threadlock isn't plastic friendly.

I've seen a few M05s (which are PC) with a crack around the shock mount screw, but nothing this bad.

[one_hit 1046]

@Kowalski86 I didn’t use threadlock. I only use that when screwing into metal. My M05 V2 Pro is also strarting to crack on the rear damper stay mounts. This one has even less run time than the MF-01X

[Kowalski86 3034]

My only theory (and I'm really reaching here) is that the extra stiffness of those aluminum/carbon hop-ups accelerated the initial stress cracks from screw insertion, whenever either of these chassis see use all of the bumps and force will be transferred straight to the cheap plastic, as its the weakest link.

My PC chassis were pretty basic, no aluminum (shocks aside) nor carbon. So all of the force would be transmitted equally. My M06 even saw a few jumps without any extra cracks.

That's my theory, either way I think Tamiya should've specified a better plastic for something that they expect buyers to really invest in.

[Sogogi 3217]

One thing i’ve read before my first tamiya build (technically it applies to many places) is not to over tight screws. Sometimes it is harder to know if it actually is tight because it is fully screwed, or just self tappers are not good. I often check the gap between body and a screw just to make sure i dont over tighten things. Not sure where those cracks are coming from, but another possibility…

[Willy iine 18806]

I think those screws were over torqued.  I think somewhere in the Tamiya manual there is a note on self tapping screws where you're only supposed to tighten until the bottom of the screw head contacts the surface.  

I checked my M05 V2 Pro just now built about ten years (?) ago.. no issue.

 

[Kowalski86 3034]

1 hour ago, Willy iine said:

I checked my M05 V2 Pro just now built about ten years (?) ago.. no issue.

If it means anything, I'd like to point out that your M05 still has the stock rear shock tower, One_Hits is carbon. That plays into my theory that stiffer parts accelerate the stress cracks on ABS/PC plastic. 

[Saito2 6686]

I'm sorry @one_hit. I wish I had more answers for you. You've definitely made me reconsider ever getting MF-01X.

[TurnipJF 9192]

I wonder if there isn't something in the environment that is attacking the plastic? Some sort of solvent fumes perhaps? Or maybe unusual temperature variations? I have both models in question, both several years old with many runs under their belts, with no cracking issues. 

[Willy iine 18806]

27 minutes ago, TurnipJF said:

I wonder if there isn't something in the environment that is attacking the plastic? Some sort of solvent fumes perhaps? Or maybe unusual temperature variations? I have both models in question, both several years old with many runs under their belts, with no cracking issues. 

I think it's a combination of things.. you bring up a good point about expansion and contraction between different materials.  I mean if the screws were tight to begin with, who knows what happens when that screw expands in hot temps.  Then contract in cold temps.

I did notice while restoring a few  (?) of M38's that the plastic varied in how brittle they were.. some were like almost crumbling.

[nowinaminute 2815]

Are the machine screws non-standard?

If so, did you tap the holes or just use a dab of grease on the screws?

I feel like sometimes using machine screws puts a lot of outward pressure on the plastic.

Not saying the plastic failing this early is OK, but I think sometimes machine screws can accelerate the failures.

[nowinaminute 2815]

5 hours ago, one_hit said:

@Saito2

I still have the sprues, it says the grey chassis parts are made of PC. I don’t think the screws are the problem because even the plastic where the rear upper arms and damper stay mount into are also cracked

You can sort of trace those all back to the screws though if you follow the cracks.

Again, not saying it's ok or normal, but I think machine screws can cause failure earlier.

I do think the grey plastic is more brittle though, so maybe between that and the type of screws it just came to a head prematurely. 

[nowinaminute 2815]

I was trying to think which car I had with the grey plastic and it was the DT-03. The front end on mine disintegrated. The gearbox section  made of black plastic seems much more durable ....

[nowinaminute 2815]

I think I might have read about owners of the lunchbox mini complain about brittle plastic, too.

[Kowalski86 3034]

3 minutes ago, nowinaminute said:

I was trying to think which car I had with the grey plastic and it was the DT-03. The front end on mine disintegrated. The gearbox section  made of black plastic seems much more durable ....

The lightweight TL01 chassis was a darker grey, and some M03s were grey. 

[one_hit 1046]

For comparison, my M03 which I built in 2010 and has seen the most racing, doesn’t have a single crack anywhere

Diff covers from my TT-02 Type S I built in 2015 started to disintegrate this year as well.
 

[OoALEJOoO 3127]

Three common enemies of anything plastic:

• Temperature
• Humidity
• Sunlight (UV in particular)

Best and easiest way to preserve your cars is to keep them inside the box and in a cool & dry place.

Sometimes it's possible that the car was older stock and it was stored by the distributor in a poor manner. I once bought a TA06, probably manufactured many years ago, and the box was moldy on the inside. Very likely its plastic won't be in the best condition.

[Blista 1519]

Mine cracked around the driveshaft area, too.  At the time it seemed unusual.  I just wrote it off as me putting the screws in too tight during the build.  It was from the initial release batches of the MF01X Jimny, but I can't recall how long before the plastic cracked.  It wouldn't have been long, though.

I think I can safely state it had nothing to do with age, aggressive driving, the temperature, UV rays, threadlock, and so on.

I no longer have it so I can't say whether the problem continued after I replaced the parts.