Will Sprint Alloy wheel nuts take a helicoil?

[GrahamFountain]

Have you tried http://www.grayston.biz/wheelnutmenu.htm

They do a wide range of wheel nuts.

There’s a guy on the Scimitar Forum that makes Stainless wheel nuts.

Think his name is a Bill and he’s based near Brighton.

I’ll try and find a His contact Details later.

It's not a problem at the moment, I have a few spares, there's a few on eBay currently, and odd few part sets turn up. It's just the garage stripped this one, and a couple of others in the spares bucket aren't great, so I was looking at what to do with those.
I knew of Grayston. I got nuts for the minilite sports from there.

[Slowmo]

Graham,

Bad luck with the experiment, don’t know what went wrong. Can’t see why the helicoil didn’t go in.

I used a lathe, and put the wheel nut in the chuck. The 9.9 drill goes in the tailstock chuck, so the drill is straight and axial.

The drill is replaced with the helicoil tap, which is then also nice and axial. I turn the lathe chuck manually for better control.

I am happy to have a go with a couple of your worst nuts if you want to risk them. I have more inserts than I am likely to use. As was mentioned, UNC is much more common for alloy.

Let me know.

Peter

[GrahamFountain]

Graham,

Bad luck with the experiment, don’t know what went wrong. Can’t see why the helicoil didn’t go in.

I used a lathe, and put the wheel nut in the chuck. The 9.9 drill goes in the tailstock chuck, so the drill is straight and axial.

The drill is replaced with the helicoil tap, which is then also nice and axial. I turn the lathe chuck manually for better control.

I am happy to have a go with a couple of your worst nuts if you want to risk them. I have more inserts than I am likely to use. As was mentioned, UNC is much more common for alloy.

Let me know.

Peter

I can't see why the coil wouldn't start correctly either. I know the fact that the tap had cockled a bit on the way in made it a bit harder to start right, i.e. correctly off line, but I still don't get it.

I'm still in two minds about whether to do anything with the remaining worst nuts or just leave them as spares. They measure about 8.5 - 8.6mm when the new one measures just under 8.3. What's confusing is that the drill size for 3/8 UNF is 8.4 to 8.5, so the new wheel nut would seem to be undersize, and these are close to right.

A bit more research gets me to the diameter at the bottoms of the threads is 9.525mm - 2 * 5/8 H, where H is 25.4/24*0.866 = 0.917mm. So that's 8.38mm.

Which is still giving the new nut as undersize. I could go see how tight it is on a stud, but then it's not new.

Maybe I'm measuring it a bit wrong - I'm using the knife edges on the inside vernier calipers, so I think I'm measuring close to a diameter. I could measure the width of the knife edges and calculate the error that gives. But I need a set of vernier calipers made by Dr Möbius or Prof. Klein to do that.

Still, it gives a relative measure - the worn ones have lost about 4 to 6 thou off a nominal thread depth of about 24 thou.

But does that mean they're still something like 3/4 to 5/6ths of good?

Graham

[Slowmo]

Measuring internal diameters of nuts with a vernier should be OK. The width of the internal edges is tiny.

Tapping drill for 3/8 UNF is 8.5 mm. I have new steel full nuts, and their inside thread diameter is 8.5-8.6mm

If your new alloy wheel nuts measure 8.3mm then perhaps they were cut with a worn tap at the factory.

The internal diameter of my fairly new 3/8 UNF die is 8.2mm, but remember that the thread tips on nuts are flattened, and don’t reach the bottom of the threads.

Perhaps your nuts are not as bad as you thought.

Peter.

[GrahamFountain]

It's possible the nuts I think are worn are correct and it's all the others that are undersize. But, given I measure at least a dozen as under 8.4mm, I strongly suspect I've made an error in taking the measurements, i.e. pushed the calipers in past the knife edges. However, it should be a consistent error, so these couple I measure as 8.5 and 8.6 should be only about 0.2 and 0.3 oversize.

The question is, how acceptable that level of wear is when 1.025mm oversize is fully stripped.

If it is just that, given they take the 48 lb.ft of torque, the only risk is they'll be the first to go when the next tire fitting gorilla gets his dirty paws on the car and gives them 100 Nm torque (again). Then that will be okay, and I'll be happy to use them.

However, if the risk is they are significantly more likely to fail in use, because they don't take the side forces on the wheel, then I think there's reason to worry, especially if I've got more than one worn nut on any one wheel.

I could test one of these worn ones and one that's still close to the new one to destruction by torquing them down till they strip - at a small risk of snapping a stud. But I won't do that if I can't repair them by helicoiling.

Graham

[Slowmo]

Graham,

I checked this morning with a random couple of wheel nuts.

Although my Sprint was built in 1977, the rear axle has 3/8 studs, so I guess a new axle was fitted at some time.

The two nuts I chose had internal thread diameters of 8.55 and 8.8mm. They both tightened backup to 50 ft-lb with not the slightest signs of ‘wooliness’.

Hope that helps.
Peter.

[GrahamFountain]

I think the problem (other than I can't tap and probably can't measure well) is I don't have any feel for what the forces on the wheel nuts and studs are in normal use, especially not how those forces relate to the tensional force that a torque of 48 lb.ft gives - which I could work out from the thread dimensions.

If I understood that, I think I'd have a better appreciation of how much to worry about nuts that have 3/4 of the thread left.

Graham

[Slowmo]

Graham,

Just looked up clamp force vs torque figures online.

3/8UNF grade 8 steel, which I think is what studs are made from.

Very approximate clamp force for 3/8UNF at 50ft-lb torque is 8000 lbs, well over three tons. Will be more with lots of lubrication. Possibly 12-14 tons for four nuts.

Surprised me.

Peter.

[GrahamFountain]

So the force on the wheel from 4 x 48 lb.ft of torque far exceeds any normal cornering forces from the mass of the car. I guess that means that if they take torque and a little bit, that's what matters. I'll still keep these as spares and go with the ones that are close to the inner diameter of the new one.

Graham