Knock-off Spinner Tightening Rationale (Yet Again)
Posted: Fri Jan 09, 2015 3:35 amI know there have been various threads on why Elan KOs tighten clockwise on the right-hand side of the car and counterclockwise on the left-hand side. This is of course the reverse of the procedure for Rudge-Whitworth KOs found in MGs, Triumphs, and several other cars.
The reason given in the book "Colin Chapman Lotus Engineering" is that in the RW system pressure on a loose spinner (being female) is at 12:00 of its inside diameter (the gap being at the bottom), while in the Lotus system pressure on the spinner (being male) will be at 6:00 of its outside diameter. (I am stating this very badly). And then of course there is the cap within a roll of tape demonstration, which shows that if you move the cap or the roll in a circular motion, without rotating it, the following cap or roll will move either in the same or opposite direction. The relationship is called "(quasi) epicyclic."
I did the tape and cap demonstration, with satisfying results, but had the following questions:
1. If the roll of tape represents the wheel and the cap inside it the spinner, why shouldn't the tape be rotated on its axis, in the same way a wheel turns.
2. Why would the spinner be in loose contact with the wheel, when we've hammered it on?
3. Finally in the roll/cap demonstration, if the roll is moved (not rotated) in a circular clockwise direction (as I assume would be the case on the right-hand side wheel), the cap will rotate on its axis in a counterclockwise motion, thereby loosening the RH Elan spinner.
I read more about this (bicycle pedals, among other things, tighten as per Lotus spinners) and the phenomenon seems to be "mechanical precession," which is explained in Wikipedia (nice moving illustration there too):
http://en.wikipedia.org/wiki/Precession_(mechanical)
I think the answers to my questions are as follows, but please correct me as necessary (I studied the wrong things at school):
1. It is not the wheel rotation that loosens the spinner, but the pressure on the contact point with the spinner (always at 6:00 in the Elan spinner, I assume).
2. As the Wikipedia article states, there is always a minute, perhaps microscopic gap between two metal pieces screwed or jammed into each other, because of elasticity and other things. This minuscule "looseness" is enough for mechanical precession to take effect.
3. I don't have the answer here. Perhaps the correct way of replicating the effect of a wheel rotating on its axis clockwise would be to move the roll (without rotation) counter-clockwise, which is the direction of the point of pressure on the spinner as it rotates.
I would appreciate enlightenment here, please. If this has been explained at length, please point me in the right direction; a search wasn't very helpful).
Then I will have to apply all that to a RW spinner to see why it behaves differently.
Many thanks, and my best wishes to all for this New Year.
Andy
The reason given in the book "Colin Chapman Lotus Engineering" is that in the RW system pressure on a loose spinner (being female) is at 12:00 of its inside diameter (the gap being at the bottom), while in the Lotus system pressure on the spinner (being male) will be at 6:00 of its outside diameter. (I am stating this very badly). And then of course there is the cap within a roll of tape demonstration, which shows that if you move the cap or the roll in a circular motion, without rotating it, the following cap or roll will move either in the same or opposite direction. The relationship is called "(quasi) epicyclic."
I did the tape and cap demonstration, with satisfying results, but had the following questions:
1. If the roll of tape represents the wheel and the cap inside it the spinner, why shouldn't the tape be rotated on its axis, in the same way a wheel turns.
2. Why would the spinner be in loose contact with the wheel, when we've hammered it on?
3. Finally in the roll/cap demonstration, if the roll is moved (not rotated) in a circular clockwise direction (as I assume would be the case on the right-hand side wheel), the cap will rotate on its axis in a counterclockwise motion, thereby loosening the RH Elan spinner.
I read more about this (bicycle pedals, among other things, tighten as per Lotus spinners) and the phenomenon seems to be "mechanical precession," which is explained in Wikipedia (nice moving illustration there too):
http://en.wikipedia.org/wiki/Precession_(mechanical)
I think the answers to my questions are as follows, but please correct me as necessary (I studied the wrong things at school):
1. It is not the wheel rotation that loosens the spinner, but the pressure on the contact point with the spinner (always at 6:00 in the Elan spinner, I assume).
2. As the Wikipedia article states, there is always a minute, perhaps microscopic gap between two metal pieces screwed or jammed into each other, because of elasticity and other things. This minuscule "looseness" is enough for mechanical precession to take effect.
3. I don't have the answer here. Perhaps the correct way of replicating the effect of a wheel rotating on its axis clockwise would be to move the roll (without rotation) counter-clockwise, which is the direction of the point of pressure on the spinner as it rotates.
I would appreciate enlightenment here, please. If this has been explained at length, please point me in the right direction; a search wasn't very helpful).
Then I will have to apply all that to a RW spinner to see why it behaves differently.
Many thanks, and my best wishes to all for this New Year.
Andy
), not particularly quickly - just keeping up with the traffic, when there was a loud clunk. The rear of the car sank down and we went into a slow spin, finally coming to rest (fortunately) at the edge of the road with both of us unhurt. The rear wheel and hub together had come off the taper. Closer examination revealed the nut rattling around inside the spinner and even closer examination revealed it to be some kind of alloy rather than steel. It had come off by leaving the threads behind on the taper. Almost certainly a D.P.O "modification" (he was a helicopter technician!)