Super disappointed with chassis plastic

[norco kid]

I Just built a new Unimog 425 and I used all stainless steel 3mm hex head screws. BIG MISTAKE! I went to remove the motor to solder esc wires and all of the gear cover screws stripped. They were not over-tightened and they actually stripped while REMOVING them. I bought some threaded inserts in an attempt to repair these from the bottom, but now the same thing happened to the screws attaching the lower skid plate while I was removing it to install the inserts! It seems that the plastic used on this chassis is very hard/brittle and that machine screws don't have a coarse enough thread to cut into the plastic and instead they "flatten" it all the way down. I've never had this problem on the other 15 or so Tamiya kits I've built. Quite annoyed because I will have to buy a new chassis and revert back those horrible Philips head screws. Worst part is I can't even to find a chassis anywhere! Tower/Amain don't seem to stock it

[58_Willys]

Sorry to hear about the screws.

There's on on ebayTamiya CC 01 Chassis Bathtub Frame Links Bumper Pajero Wrangler Land FJ Cruiser | eBay

[EeePee]

Stripping a thread while removing a screw doesn't make any sense at all.

[norco kid]

Originally Posted by EeePee

Stripping a thread while removing a screw doesn't make any sense at all.

I wouldn't believe it myself if it hadn't happened to me. I drive the screws in only until snug and stop. When I was removing it I was turning counter clockwise and the screw came out about halfway and then just kept spinning and spinning without coming out any further. I had to apply a little bit of outwards pressure to the head with a flat head screwdriver while unscrewing it to get it out. Maybe there was so much friction while threading it in that it heated up and melted the plastic? I was also thinking that because the gear cover is a separate piece that the screw passes through maybe it somehow caught the screw and held it down causing it to strip the chassis part while unscrewing? Also the stripped threads are almost powder like, not little strands of plastic that I typically see with stripped screws. That's why I say it is the compound of the plastic itself that I am disappointed in. The screw comes out with a white-ish powder on the threads.

[norco kid]

This a screw that I took out from the lower skid plate:



Here you can see what I did to repair the gearbox cover screws. I wanted to make sure these screws were secure to prevent any gear stripping issues. I used a brass insert for the 2 screws along the chassis center line and drilled right through and used lock nuts for the other 2 (near u joint and the one above the steering rack)



My problem now is that the skid plate screws have stripped and I can't use an insert on these since some of them have gears behind them.

[OSRC]

That is odd. I've had 10+ of these little rigs and never that kind of problem.

Put some CA on a toothpick, and swirl it around in each hole. Not a ton, just a thin coat. Will bond to the plastic, make the circumference of the hole smaller, and the screw will bite again.

[stevetate12]

The screws you used whatever replacement screws they were ..were clearly too big or just the wrong type ....this could.be proven by trying to use the screws that came with the kit and if there's nothing for them to grab onto ..well ......ive built alotta taliya stuff and because its plastic ive never felt the need to.use heavy duty nuts and bolts.....its just not necessary.............the point your at now is either ca glue..etc....or but another peice that contains the bolt holes that are stripped

[HDMM]

I agree ^^^

The original screws are a coarse thread similar to a sheet metal or wood screw. The ones you used are a machine thread which actually will fit a lot tighter in a hole that was meant for their coarse thread screws.

I found the same thing when using a stainless screw kit on a SCX10, they fit much tighter in the holes designed for coarse thread screws. In the Axial, it was a good thing as they use much softer plastic than Tamiya.

[Polar]

I had a similar problem, it was caused when screwing in the screws, but not discovered until I came to remove them.

The screws I removed looked just like yours, with bits of plastic stuck to the thread.

The issue I found was using too much speed (Or force) when putting the screws in, causing the plastic to melt. This holds the screw fine once, but when you try to remove it makes a right mess.

I now turn the screws much slower and all has been good. I have also invested in a low torque electric screwdriver and that helps too.

[OSRC]

Originally Posted by Polar

The issue I found was using too much speed (Or force) when putting the screws in, causing the plastic to melt. This holds the screw fine once, but when you try to remove it makes a right mess.

This. Exactly. Don't even have to be going that fast. Tamiya uses ABS plastic, very susceptible to heat.

[chino63]

Like said above, there is alot more surface area on a machine screw than the self rappers supplied with the kit.

I recommend tapping the holes (by hand) for helicoils if you are using machine screws. Set them with a drop of thin CA and let dry before installing the hardware. I have done this to many Tamiya kits and they hold up for many many disassembly/assembly cycles.

Also, DO NOT use thread lock on any hardware going into the Tamiya ABS, it will become brittle and literally fall apart.