SlotForum banner rear wheel grub screws too tight

2757 Views 34 Replies 21 Participants Last post by  Martyn_
I've just bought a new Audi R8C (CA12C) which has had its rear wheel grub screws over-tightened in the factory. I've ruined three new allen keys trying to loosen the screws, only have two undamaged allen keys left and don't want to ruin those. I need to loosen the grub screws to reposition the rear wheels, which have been fixed too far inboard at manufacture.

I've tried alternately gently heating and cooling the axle and wheel assembly, which succeeded in loosening one screw, but the other is still jammed tight. Any ideas how to undo it?
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I am sorry that you had this problem, but I really can't remember many other occurences of this happening.
We have been using these screws in all parts and cars for 14 years with no problem, if used with a good tool. People changes wheels and gears quite often on our cars and parts as some other racers say.
A bigger grub screw is two to three times as heavy, thus creates much more vibration when spun at high rev. It is a noticeable difference.
Besides, a bigger grub screw would leave less metal on the threaded side, and I've seen several wheels break due to this.

As for the tool, I had missed that thread, and we'll see what can be done. Chapman would you please contact me.

In fact, the reason we make the magnesium wheels with asymmetrical design is to compensate the greater weight of the grub screw moving material around.
The vibration caused by the screw can be appreciated by spinning an axle in the motor mount with and without screw. To me, the fact that it can be easily detected, at the moderate speeds spinning the axle with fingers, means that it is not without an influence at higher RPM, but of course I may be wrong. I agree that motor and tyre are a greater source of vibration, but this doesn't mean I shouldn't try to design a more balanced wheel anyway. I also always do what John says. Is it worth 0, 0.001, 0.01 seconds? I don't know honestly.

As for the tip, it is 48-50HRC - this is what we use and the steel of the tip may become brittle at hardness higher than that. I use the 'torque limited' tool and I don't remember ever having stripped a thread or loosing a race due to lost wheels or spinning crown. You may believe me or not but I also have some experience on this over the years. For the torque that the hard bodied cars and motors have to cope with, these grub screws are more than adequate. They must be handled differently from what is done in BSCRA type of racing because in our case it is not necessary to apply all the torque that may be necessary in other situations.

The limited torque tool is otherwise used to tighten grub screws in pacemakers so it is a pretty accurate tool. I suggest using it - not necessarily, there are others in the market, but they're are a sure way to avoid such trouble.

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