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Z320

are whire wheel center caps self-tightening

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Hi @,

not very often I've been told whire wheel center caps are selftightening, perhaps two times in 10 years.

But this year my impression is I've been told that 10 times!

But I think they do not because the whire wheels are teethed on teethed adaptors and cannot turn the cap.

And if they would be selftightening while I drive, wouldn't they be self slacking when I brake?

Out for a test today....

Ciao, Marco

 

Edited by Z320

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They do self-tighten, the wheels do not have to rotate on the splines, they just need a tiny lateral movement (upwards due to gravity pulling the adaptor downwards)

As the wheel turns that tiny movement is moved around the circle of the splined hub, taking the spinner with it. the effect is a sliding movement between spinner & hub.

This is why the threads are in the opposite direction left & right side.

When you brake it makes no difference, but if you drove a long distance in reverse you could loose your wheels !

 

Bob.

Edited by Lebro

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+1 Bob ~

I would call it the 'Inertia' effect. That's why the spinners are 'handed'. If you fit the splined hubs the wrong way round then they would self loosen.

The spinners are marked with an arrow showing which way they should be tightened. Left hand axle = 'Right Hand Thread'

"Right hand axle = 'Left Hand Thread'. The photo. shows the 'Left Hand Threaded' spinners.

Tom.

DSCF1546 - Copy.JPG

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Inertia has nothing to do with it !

it is the action of two circles of slightly different diameters rotating together, but only touching at one spot (at the top).

This happens when the two cone profiles are not forced together

The larger diameter one (spinner) will rotate more slowly, & so will tighten it's self onto the smaller dia one (wheel)

Once all the free movement had been removed then they will rotate together

Bob

Edited by Lebro

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And if you fit the adaptors & spinners to the incorrect sides of the vehicle, they will be sure to undo themselves, as Paul Hogan can verify as - many years ago - he nearly lost a wheel (or probably more than one)!

I believe Bob's explanation of the self-tightening to be correct.

Ian Cornish

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I had my doubts about Bob's explanation a long while ago but when Bob explained it it all clicked.

It is only possible because the adapter and wheel hub do have a some play.

It the spline fit was perfect then it wouldn;t tighten - but then again it wouldn't undo.

 

Roger

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Hi Bob,

thanks for this explanation, this sounds reasonable.

This is what I did yesterday: I slacked all 4 wheels (I tighted them before with about 300 Nm),

re-tighted them with only about 200 Nm and marked the wheels and caps with an Edding like on the photo.

P1130639-b.JPG.a074d13cb32783776f41aab882e9f397.JPG

After a 150 miles drive today with some TR-friends (fast country roads, up and downhill) I checked them.

They are still exactly the same on all 4 wheels. So it seems the self tightening effect can't lock the caps more than 200 Nm.

I ask myself: should I do the test again with only 150 Nm....

How strong can the self tightening effect lock the cap?

Ciao, Marco

Edited by Z320

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Hi Marco,

perhaps the 'self tightening' is the wrong phrase

More importantly they are not "self UN tightening".

Does it matter how tight they are - just as long as they are tight enough.

If the spinners are on the wrong side of the car there is every possibility that they WILL self UN screw.

 

Roger

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Bob,

tremendous explanation, thanks.

Just wondering, in Marco's case, is ther a diference between the effect on

Octagonal Nuts, as opposed to Spinners?

John.

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Hi John,

it is the contact area that counts. The external shapes is of no matter.

I think Bobs explanation with my little bit of input above gets nearer the answer.

 

Roger

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Hi Roger,

self-locking and selt-tightening is a difference, self-locking is not the question.

People who told me "they are self-tightening" did it in the conviction:

tight them anyway, don't matter how tight, the rest will find ist way, because they are self-tightening.

Ciao, Marco

 

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Hi Marco,

what I was saying is that if they are fitted to the wrong side they will become - Self UN locking.

No matter how tight they are they will UNlock if they are fitted wrong.

 

Forget self tightening

 

Roger

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Interesting topic.

I think the friction on the threaded part and the friction on the conical contact area play a role too. If one is low and the other is high, this may make a difference.

MWS which is one of the leading suppliers indicate on their website they are self locking:

http://www.mwsint.com/site/cms/contentCategoryView.asp?category=214

Also, MWS does not provide a torque figure.

Maybe Marco’s applied torque was already high enough so no further tightening could occur while driving?

Waldi

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Anyone with wire wheels is invited to lock the cap as he always does, mark them with an Edding and report.

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Every day is a school day on the forum....Google is your friend:

Edding. 

Edding AG is a German company manufacturing writing and marking tools such as felt-tip pens and permanent markers. The company's products are immensely popular in Germany, leading to the brand name "Edding" being widely used as a generic name for permanent markers, quite similar to Sharpie in the United States.

B)B)B)

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Found this schematic to illustrate Lebro's explanation. 

 

spinners_dia.thumb.jpg.7774726d4ef6e6142b7699fbe40fba01.jpg

 

 

 

spinner_1.jpg

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It is as Bob says, and the tightening effect only goes so far until friction stops it going further. The effect Marco is called "precession" (Präzession auf Deutsch?) but I only know this because of explaining to people why bicycle pedals are also threaded the opposite way to what you might think.

Cheers, Richard

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Hi Richard,

sorry, I expect "precession" does not work at all on the front axle because they are not powered / driven but only pushed.

Marco

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It works just the same on the front, nothing to do with whether shaft is driven or not, it is simply the weight of the vehicle on a loose cone shaped connection, combined with rotation.

Bob.

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Wheel nuts same same..

Rolls Royces of the 1960s and Alfas of similar vintage have reverse-threaded wheel studs on left side of car for same reason...sure confuses the local tyre shop monkeys

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10 hours ago, Lebro said:

It works just the same on the front, nothing to do with whether shaft is driven or not, it is simply the weight of the vehicle on a loose cone shaped connection, combined with rotation.

Bob.

Hi Bob,

your explanation seems reasonable to me, but precession is a different thing,

working on not teethed (powered?) shaft, where the power of the rotation tights the thread more and more, like on pedals of bicycles (LH thread on left side).

Another think in my opinion is inertia for example on the left side of a grinder bench, on a angle grinder or a circular saw (blade), not on the wire wheels of our TRs!

Ciao, Marco

Edited by Z320

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10 hours ago, ctc77965o said:

Wheel nuts same same..

Rolls Royces of the 1960s and Alfas of similar vintage have reverse-threaded wheel studs on left side of car for same reason...sure confuses the local tyre shop monkeys

Hi dave,

Now you've done it - total confusion.

On the TR the left side has a RH thread. The right side has the 'reverse' thread - opposite to your post.

Is this because on the TR we are referring to a spinner on the rotation axis and on the RR the wheel studs/nuts are off centre.

 

Roger 

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 I think It all depends which bit is driven Roger, the inner or outer component of the bolted system. I seem to recall that on some early cars (not TRs) the hub retaining nut is handed the opposite way to the corresponding wheel spinner. i.e the axle nut on the rhs is rh thread but the wheel spinner is lh thread and vice-vera on the other side.

Confusion reigns.

Edited by RobH

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Early Ford Transits used to have left hand thread wheel nuts on one side too.

Stuart.

Edited by stuart

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