Undersized threads and what can be done?

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steveo
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Undersized threads and what can be done?

Post by steveo » 01 Feb 2019, 19:29

For those of you following my build, you'll know that my front lower wishbone is a slight variation from the book. One of the major changes is the use of a Moog ES2074R ball joint as the upper ball joint to mount the spindle as can be seen here:

Image

I bought the ball joints some time ago, but only this week got the threaded inserts (M16 x 1.5) to mount them. This uncovered a problem...

When I screwed the ball joint into the insert it was sloppy. While the threads and sizes were right it was not a nice snug fit like on every other joint I have. It's sloppy enough that it concerns me.

I went back and checked the parts and the insert from McGills was bang on, but the large thread on the ball joint which is supposed to be an M16 x 1.5 is actually a M15.9 x 1.5. Now 0.1mm may not be a great deal , but it does leave it feeling sloppy, and seeing as the car is depending on this it's enough to concern me.

Any ideas on what can be done here? I don;t really just want to get replacements as the same poor dimensions may show up again. My thinking is to weld a tight M16 x 1.5 nut onto the end of the insert to give it a tighter thread inside the tube and more support.

Any thoughts?

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Re: Undersized threads and what can be done?

Post by freakynami » 01 Feb 2019, 22:03

Use of a jam nut will draw the threads into contact on one set of faces, which I can't imagine is any different to a tighter thread that will still pull up in the same way, just a bigger "gap" for you. I'd also use purple loctite (or whatever) which will set hard and take out any slop. I'd doubt either of the threads will actually fail.

Or try some thread tape?

Out of interest, 5/8-18 is Ø15.875 x 1.41 - just sayin'...

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Re: Undersized threads and what can be done?

Post by Midlana1 » 02 Feb 2019, 07:34

Locktite also has stuff to save slightly oversized bearing seats. Had to use it on Kimini once and it saved a lot of work. Of course, Locktite knows this and sets its price real high.

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Re: Undersized threads and what can be done?

Post by rennkafer » 02 Feb 2019, 18:24

There are a number of different kinds of bearing mount Loctite. I've always used 680 to good effect for loose bearing race/thread fits. Like Kurt said, it ain't cheap for how much you get.
https://www.amazon.com/Loctite-442-6801 ... B000O05BXW
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Re: Undersized threads and what can be done?

Post by steveo » 03 Feb 2019, 07:28

Thanks for the feedback guys. Didn't know about purple loctite!

First though I'm going to follow freaky's lead about a different thread size. A quick trip to Ace will answer that one.

If that doesn't work then purple loctite seems the way to go. I was initially concerned that this makes the suspension less adjustable, but the same effect can be had by adjusting the inboard mounts, although there are two of those.

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Re: Undersized threads and what can be done?

Post by Midlana1 » 03 Feb 2019, 09:04

steveo wrote:...I went back and checked the parts and the insert from McGills was bang on, but the large thread on the ball joint which is supposed to be an M16 x 1.5 is actually a M15.9 x 1.5.
How did you measure the thread pitch, because I could find no reference to M15.9 being a standard size. My guess is that one (or both) parts instead have a very poor tolerance M16 thread rather than being purposely manufactured as M15.9. If it's an option, try new parts, maybe from a different vendor.

http://www.professeurs.polymtl.ca/luc.b ... THREAD.pdf

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Re: Undersized threads and what can be done?

Post by steveo » 03 Feb 2019, 20:44

Lol! No. What I meant was that they probably intended it to be an M16 but for some reason or other it has turned out as an M15.9.

I checked the ball joint against some M16 nuts at Ace and they had the same slop.

What concerns me is that the ball joint will be subject to some fairly high vertical loads so while loctite would work great if this was just subject to lateral loads I would imagine that over time the loctite or whatever I use would wear down and once a little play gets in there it’s going to grow fairly quickly.

So, I could try returning them and moaning about the size ...

Or, as I now have a lathe, I can machine some
M15.9 x 1.5 inserts. Sounds like a challenge!

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Re: Undersized threads and what can be done?

Post by Webster » 04 Feb 2019, 12:52

Turning up made to fit inserts would work , we do that at work when we want a specific thread fit .
my only concern is that if the ball joints you have are not as meant to be and when you eventually replace them , the new ones might not fit the custom inserts.
This does seem unlikely , but is the only possible issue I can see with making your own inserts.

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Re: Undersized threads and what can be done?

Post by steveo » 04 Feb 2019, 13:10

Yeah whenever you go custom you’re creating the possibility of future problems. Before I go custom I’m going to try another pair from another manufacturer but ordered through the local store so I can return them if they’re still not manufactured to spec.

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Re: Undersized threads and what can be done?

Post by freakynami » 05 Feb 2019, 01:20

The only other thought that comes to my mind, is to modify the threaded bush you have, by cutting a slit through one half, then working out some way of "clamping" down on it once the thread is engaged to where you want. This way you can still use all the bits you have on-hand, and when you replace the bearing down the track you can adjust to suit whatever you end up getting again.

Something like this is what I'm picturing...
SteveO's Suspension Arm.png
I'd weld it all together, then drill a hole to reduce the likelihood of cracking, then slit it, carefully...
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