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  #1 (permalink)  
Old 02-09-2022, 08:00 PM
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Default ERA steering wheel hub threads

I completed my car with the ERA-supplied 15" steering wheel, which is held to the hub with six 12-24 flathead screws. Since this wheel does not have a split center, there is no separate top ring - the screw heads tighten into countersunk holes in the wheel itself.

I've just bought a Moto-Lita 16" split-center wheel and the top ring that goes over it. These parts have the same pitch circle diameter and hole staggering as the ERA-supplied wheel and hub, so everything lines up fine.

However, the hardware pack from Moto-Lita contains significantly larger screws - M6 - along with corresponding locknuts. The holes in the wheel and the countersinks in the top ring are sized to accommodate these screws.

So here's the question: is it necessary to drill and tap my ERA hub to M6 and use the bigger screws?

I've mocked up an assembly with the original screws and it seems okay. Since the screws locate on the countersink of the top ring, I'm not particularly worried that the clearance holes in the wheel are oversize.

The added height of the top ring robs some thread engagement in the hub, so even if I stick with 12-24 I will probably replace the original screws with longer ones to gain that back.

Bill
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  #2 (permalink)  
Old 02-10-2022, 04:59 AM
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Not sure I know the ultimate answer but they do make conical washers that would give your screws more purchase on the beveled seats in the wheel.

https://www.summitracing.com/parts/e...yABEgLGAfD_BwE

I think they make these in soft copper too - I’ve read of their use in sealing up fuel lines to carburetor seats that would not seal up on their own.
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  #3 (permalink)  
Old 02-10-2022, 09:22 AM
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Correction: the original screws are 10-24, not 12-24. So the difference in screw diameter is 0.190 (existing) vs. 0.230 (new).
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  #4 (permalink)  
Old 02-10-2022, 10:28 AM
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It is not possible to drill out a 10-24 hole and rethread it for a 6mm fastener. The problem is a major diameter, minor diameter conflict issue. The next size up fastener needs a thread that uses a tap drill which will entirely clean up the hole, when properly sized for the new fastener, prior to tapping the new thread. Your situation does not provide you this opportunity.

You have several options available to you without changing to another wheel;
  • Use a larger fastener,
  • Offset the steering wheel hub by 3 or 4 splines (if it is not keyed) and drill the hub for 6mm fasteners,
  • If it is keyed then you need to make a new hub,
  • Learn to love the old steering wheel.
Putting 6mm hardware into 10-24 holes is asking for a mechanical failure.


Ed
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  #5 (permalink)  
Old 02-10-2022, 10:40 AM
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Ed,

The tap drill for M6 is 5mm (0.197), which is larger than the major diameter of a 10-24 internal thread (0.190). Therefore drilling to tap at M6 should leave a clean hole with no compromised material at the crest of the tapped female M6 threads.

Last edited by fintubi; 02-10-2022 at 10:51 AM..
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  #6 (permalink)  
Old 02-10-2022, 11:03 AM
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For a mere $850 you could get the ERA Quick Release hub. It is literally a joy to own. Click Me for the ERA Options list

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  #7 (permalink)  
Old 02-10-2022, 02:21 PM
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Quote:
Originally Posted by fintubi View Post
Ed,

The tap drill for M6 is 5mm (0.197), which is larger than the major diameter of a 10-24 internal thread (0.190). Therefore drilling to tap at M6 should leave a clean hole with no compromised material at the crest of the tapped female M6 threads.
You have a 0.007" diameter difference and a 0.0035" difference per side. This is small. I would definitely consider just using a 5mm reamer to bring the hole on size for tapping and forget the drilling idea. Even jobber length drills in a mill do not produce the precise sizing the reamer alternative does. With as little material as you have to work with there is no room for a whoops.

You can find a 5mm reamer at McMaster-Carr, click here => 5mm Reamer.

BTW still use a drill press or mill for a straight precise 5mm hole. If you use a mill do not forget the head is movable and may have been moved by the last guy who used the mill. That means you need to zero the mill before reaming the hole.


Ed


p.s. To do this job correctly you should use a mill. Use a gauge pin that matches the ID of the original screw hole to locate the true bolt hole center. Make sure your mill has a digital read out for the x-y position of the table. I have an Excel spreadsheet that will give you the x-y co-ordinates for each of the six holes. If you go this route and need the spreadsheet send me an email and I'll send it to you. The forum has my email address and will allow you to email me. I will send you the Excel spreadsheet. It is very intutive and will work up to some large number of holes, providing you accurate x-y coordinates, out to as many decimal places as you wish.

p.p.s. I just remembered, the Moto Lita PCD is not evenly spaced holes. I have a document with the correct x-y positioning coordinates for the unequally spaced holes. Same offer, email me for a copy.
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Last edited by eschaider; 02-10-2022 at 02:39 PM.. Reason: Added Postscript
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  #8 (permalink)  
Old 02-10-2022, 02:34 PM
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Quote:
Originally Posted by patrickt View Post
For a mere $850 you could get the ERA Quick Release hub. It is literally a joy to own. Click Me for the ERA Options list


This is a waaaay cool piece that Patrick is promoting.


Ed
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  #9 (permalink)  
Old 02-10-2022, 02:48 PM
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Quote:
Originally Posted by eschaider View Post
This is a waaaay cool piece that Patrick is promoting.


Ed
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  #10 (permalink)  
Old 02-10-2022, 03:29 PM
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Does it include a soda?


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  #11 (permalink)  
Old 02-10-2022, 04:21 PM
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Thanks, all. A couple of other thoughts:
  • The QR hub is indeed super cool. But since it's typically supplied with the standard steering wheel, I'd expect that it's tapped for 10-24. So it would only address the issue if a new one is custom-tapped to take the Moto-Lita screws, or if 10-24 screws are used.
  • The Moto-Lita hardware comes with locknuts, so they're assuming that the wheel will be mounted to clearance holes rather than tapped ones. The tapped holes in my hub are through holes, not blind - so if there is space for the nuts on the back side, it may be possible to open up the existing holes to clearance for M6 and dispense with tapping altogether. I'll have to examine the back side of the hub to see if this is an option.
  • Lastly, I'm not convinced that there's any problem mounting the new wheel with the existing hardware. The old screws take up fine on the countersink of the new wheel; so as long as thread engagement is maintained nothing else has changed. That was really the original intent of my post: lots of people use the M-L wheel, so there must be a standard practice here. I'm aware of at least one other car where this wheel was swapped into a build at ERA; so far as I know, without any heroics needed.

B
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  #12 (permalink)  
Old 02-12-2022, 11:21 AM
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You could drill the old threads out and install the M6 helicoil you need. Kits are available on MSC or McMaster.
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  #13 (permalink)  
Old 02-13-2022, 08:30 AM
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Why not just use longer 10x24 screws?

If you are interested in the quick release hub, call Peter and ask him about it.
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  #14 (permalink)  
Old 02-13-2022, 06:14 PM
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Quote:
Originally Posted by RockBit View Post
Why not just use longer 10x24 screws?
That's the plan of record. The old screws work, but I've got longer ones coming tomorrow which will accommodate the thicker stackup without sacrificing thread engagement in the hub.
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