SlotForum banner rear wheel grub screws too tight

2768 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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Chris A, I can assure you I have experienced this problem with a Slot.It grub screw on my Lola and don't appreciate being called a wind up merchant. I have been racing on and off for nearly 50 years and haven't experienced this problem with the larger size grub screws. I have snapped a hardened wrench to get one out but it came out and I just ground the wrench down.
Maurizio, I can't believe that at the revs most hard body cars use a larger grub screw can make much difference. With a larger grub screw you remove more material from the wheel, I realise that there is a weight difference between the wheel and grub screw material but it must be extremely small. At the position it is being near to the axle it can't make any difference. In BRSCA 1/32nd sports strap motors they are pulling over 150,000 rpm and they use the larger grub screws in gears. The latest thing for the really fast guys now is to balance gears and wheels and tyres, this is mainly due to in consistency in manufacturing though
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Interesting CJA like bigtone, others and yourself i have been around a long time about 50 years and i do know what i am talking about, if you read the other comments about Slot it grub screws we are not alone in this problem which i personally have found annoying, as far as wind up merchants go a man of your years should show some respect when people are having a problem and if you were a true fan you would be offering help and advice instead of making remarks which belittles your years, Keith.
QUOTE ( @ 18 Sep 2012, 08:59) <{POST_SNAPBACK}>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.
I agree, and the balance issue is yet another reason to consider manufacturing your axles with flats on each end. I'm making an assumption (always a dangerous thing and I could be wrong) that the grub screw weighs more than the amount of alloy removed when the screw hole is cut, thus rendering the wheel/screw combination unbalanced. Adding an axle flat will; 1) move the grub screw marginally closer to the centre of rotation, reducing vibration (although possibly almost imperceptibly), 2) The localised loss of axle weight caused by grinding a flat goes someway to offsetting the added weight of the grub screw, again reducing vibration. My maths isn't good enough to calculate the forces involved at high revs, but the improvements should be easy to prove for someone who knows the equations, and 3) you could advertise your axle assemblies as "dynamically balanced", which would, I'm sure, be a hit with many buyers.

QUOTE (Screwneck @ 18 Sep 2012, 06:07) <{POST_SNAPBACK}>Heating up light alloy and metals will cause the material to expand faster than the bolt and thus crush the bolt in tighter and even ruin the internal thread.
Response 1: Bingo. That's the reason for using a heat/cool/heat/cool cycle; the different rates of expansion can sometimes free the bolt.
Response 2: What? The alloy expands faster than the steel so will crush the steel? How does that logic work? If you're in any doubt and have access to a photo editing program (or a magnifying glass), photograph a wheel and enlarge the picture slightly to replicate the effect of heat expansion. The grub screw hole gets bigger, not smaller.

QUOTE (Screwneck @ 18 Sep 2012, 06:07) <{POST_SNAPBACK}>You have also probably already stripped out the hex bolt hole.
Nope. Not everyone is a ham-fisted ape. Even if I was, the tool isn't hard enough to damage warm chocolate, let alone a grub screw.

QUOTE (Screwneck @ 18 Sep 2012, 06:07) <{POST_SNAPBACK}>use WD40 penetrating spray or 3-in-1 oil. A tiny drop in the bolt hole is all you need.
That didn't work.
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Reducing vibration does make a difference to the faster cars. I cannot say I've noticed much difference with hard bodied cars, but it's possible a top driver would be able to detect a difference.
Unless the motor is dynamically balanced, its likely there will be far more vibration from the motor than the wheels.

If you really want a wheel/tyre that is in balance, the only way is to balance it with the tyre glued and trued.
Wheels can be balanced before fitting the tyre, but the balance usually changes somewhat with the tyre fitted. Just occasionally there's one that's pretty much in balance without doing anything, but mostly I find I need to add some balancing weight to the wheel each time a new tyre is fitted.
Putting a flat on the axle would change the balance, normally this would just make it a different amount out of balance, although just occasionally one might end up in static balance. Many but not all the wheels I've balanced are heavy on the grub screw side, so putting a flat on the axles would make the balance better on some wheels and worse on others. That sure isn't dynamic balance.
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Regarding wheel /axle balance, one thing I got used to doing on the fast BSCRA type cars was to stagger the position of the grub screws so they were not all lined up along the axle. Probably didn't do much but the difference might be about the same as what you would get between 2mm and 4.40 UNC grub screws.
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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Maurizio, I am a big user and fan of your products, but the one item in the range that falls short, is the M2 grub screw wrench, the one with the orange moulded handle ........................ On my example the corners of the hexagon were already rounded off when it was new. I am sure that you know, the corners of the key need to be sharp and a precise fit into the grub screw for the system to work successfully. It's the corners that do the driving........... In my case after about 6 screw tightenings the wrench was useless, it went to the place where the sun doesn't shine ! !
I now use the NSR wrench for M2 screws, the hexagon tip is ground and hardened and after 10 months use and many, many wheel changes, is still as good as new. I think you need to look at your current design to bring this item in line with your generally high standards ! !
I will even design one for you if you want ! !
Hi guys.
There is no problem with the theory of the 'small' Slot It size allen head fastner. Three problems occure with its use.
1.Over tightening, very common, leading to the second problem; Head rounding; this quite small head requires a good fitting tool, correctly aligned, to facilitate regular installing and removal of the screw.
The third problem is very small!! As some of the above posters have pointed out, being 'very experienced' does mean you won't be seeing your 21st birthday again, and your eyesight is not as good as it once was! (I to am in this group).
The small allen head screw needs, a well made wheel hub of good quality material (all Slot It wheels are made of good material) a well tapped thread, and a good quality screw. Some of the screws fitted to slot It and other quality wheels are not to the same standard as the wheel hub, something that could be improved, Finaly the wrench; I don't use the Torque version, prefering to use my own abilty to 'torque' nuts, bolts, screws etc. Buy a really good quality wrench and replace or re-dress the tip often.
If you take care, these small allen screws are reliable and I have slot It wheels that go back years, with lots of regular racing use and are still giving good service.
Kind regards Bill.
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I'm slowly learning the trick of getting the torque correct - had a few tears along the way, but I'll get there. Hobby has seen the result of my over-zealous tightening, first hand.

I've got the MBSlot torque wrenches - I find them fine for NSR larger grub screws, but I manage to over-torque the smaller Slot.It grubs. I wonder if I can easeit back a few tenths of a NM?

John- I don't normally agree much with gooners, but funnily enough I do that myself, just out of logic - and I'm a real wet behind the years slotter. I thought back to how my old Laverda triple used to just about not shake itself to bits by staggering the pistons at 120 degree intervals.
Maybe easier to buy but sometimes alchemy is fun.

One can make one's own penetrating fluid with a bottle of nail polish remover (acetone) and some ATF (automatic transmission fluid) . Just mix 50/50 shake before use.

Oh and as I only have cheapie L shaped Allen keys. Tighten using the long end inserted into the screw and remove with the short end inserted in the screw
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1. The larger NSR bolts obviously do not create an imbalance of any noticeable proportion or NSR wouldn't make such fine performing cars, would they?

2. Thanks Dopamine. You obviously know what you're doing and you must be 100% correct on all counts, so carry on regardless of what you clearly see is rubbish advice! But if you are right on all counts, how come you can't get the bolts to move?

3. I've seen several posts in the past over a few years when these SlotIt bolts have been mentioned as being fragile.
When handled correctly slot it also produce very fine handling cars. I would be inclined to agree with Mauritzio here as I am sure he knows his stuff and has spent countless hours researching this or having it researched.

The Allen keys you get with the cars are not that great admittedly, and the bolts can round up. But with a decent torque tool, I use the slot it one previously mentioned and it's fine, others use other brands, the bolts are fine. I don't know anybody that uses the free Allen keys, a decent Allen key and your life will be a lot easier.

Plus most people want to adjust the width which the wheels sit at rather than just having them over a designed flat area or something
the proper penetrating sprays are very very thin and smell like petrol. if that doesn,t do it, your on the right track with heat, only you undo it while its still hot. ally will expand more than the grubsrew, so it will be easier to undo. contra to what you,d expect, if you try to tighten it before undoing it, it usually breaks the tension between the treads and comes undone pretty easally. a stripped 2mm thread is exactly the right size for tapping a 2.5mm thread. if your worried about weight gain , drill right through the grubscrew to make it hollow. the drill size is the round end of a drill that spins easally in the hex part of the grubscrew. be carefull when drilling and use coolant as the grubscrews should be hard-tough. john
I'm astonished that this thread has reached a third page. What started as a simple request for ideas for loosening factory overtightened grub screws has clearly hit a chord with many users who have expressed varying degrees of dissatisfaction and frustration with's grub screws and tools.

Personally this is the one and only time I've had a problem with them. I'm satisfied that it was a fault of the factory and not an inherent design or quality flaw, but the volume of responses does suggest that not everyone is entirely happy.

QUOTE (Screwneck @ 19 Sep 2012, 06:42) <{POST_SNAPBACK}>2. Thanks Dopamine. You obviously know what you're doing and you must be 100% correct on all counts, so carry on regardless of what you clearly see is rubbish advice! But if you are right on all counts, how come you can't get the bolts to move?
You're welcome Screwneck. It won't come as any surprise to you that I consider most of your pearls of wisdom and "advice" to be utter BS and thoroughly misleading for those new to the hobby.

As stated, the screws were overtightened in the factory. I could easily have moved them by hitting them with a hammer, using dynamite, cutting a slot for a screwdriver (a sensible suggestion but a last resort) and many other methods that caused irreparable damage, but I chose not to. Instead someone suggested knocking the axle out of the hub. That worked perfectly and the car is now happily purring around my track, still using the original grub screw and hub, with no damage done.
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QUOTE (Dopamine @ 19 Sep 2012, 11:26) <{POST_SNAPBACK}>... Instead someone suggested knocking the axle out of the hub. That worked perfectly and the car is now happily purring around my track, still using the original grub screw and hub, with no damage done.

Glad you cleared up that bit, I made an assumption that the screws had been removed but the axle was not shifting in that instance. I need to go back and reread that whole section of the thread.
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