Going a little in depth with the front suspension
- Thread starter sdibbers
- Start date
"Given that is phenomenon does not occur in a road-going car suggests that the design is perfectly satisfactory for that application."
In fact it was not. There is an early service newsletter entry about suspension knocking caused by the "protective coating" being worn off the bar & clamps. There was a production change to that coating, and attention was directed to retightening the clamp bolts.
I was also fairly certain I'd read a note suggesting the bolts were upgraded to high tensile, but the part number remains the same so I think that was another clamp bolt somewhere on the car.
Yours
Vern
In fact it was not. There is an early service newsletter entry about suspension knocking caused by the "protective coating" being worn off the bar & clamps. There was a production change to that coating, and attention was directed to retightening the clamp bolts.
I was also fairly certain I'd read a note suggesting the bolts were upgraded to high tensile, but the part number remains the same so I think that was another clamp bolt somewhere on the car.
Yours
Vern
The ARB I made has 17mm hex ends as per the original bar. That ensures a good amount of clamping surface area between the clamps and bar. The exposed center section of the bolts isn’t really any different than if the clamps and bar were perfectly aligned without gaps. The screws would still be stretched under load but hidden inside the clamp bodies.
The gap is there for a reason. The bar doesn't just twist it bends slightly in the other two planes (or tries too). The gap allows the cap and arm to move slightly as the bar moves while ensuring the clamp forces on the bar faces are constant so the surfaces of the bar remain in the same location in relation to their mates. Mating the cap to the top arm will both reduce the clamping pressure on the bar faces and cause the bar to move relative to the cap when the bar bends (as in when it reacts to one wheel hitting a pothole). In standard form the cap can move with the bar. Note also that the bar doesn't twist along the centre line of the top links; it's slightly below.
M
M
Hi Vern,
That's part of the iterative design process. If the initial design requires a slight modification, as in the case that you cite where a protective coating was worn off, then changes are made so that the problem is corrected. I am assuming that may have been relatively early, during the 1960s, perhaps?
I have never had to tighten the ARB bolts on my Rover at any time between spring removals, so obviously, the problem was fixed.
Ron.
That's part of the iterative design process. If the initial design requires a slight modification, as in the case that you cite where a protective coating was worn off, then changes are made so that the problem is corrected. I am assuming that may have been relatively early, during the 1960s, perhaps?
I have never had to tighten the ARB bolts on my Rover at any time between spring removals, so obviously, the problem was fixed.
Ron.
Hi Mike,
The bending in the orthogonal planes is why the Polar second moment of area (J) is used to describe the member's resistance to torsion about the longitudinal (z-axis). J is the summation of the second moment of area about the x-axis (Ixx) and the second moment of area about the y-axis (Iyy). Ixx and Iyy describe the member's resistance to bending along each of those planes.
What makes matters more challenging is that a bar with hexagonal cross-section does not behave in the same way that a bar with a circular cross-section does. The latter is axisymmetric; the shear strain varies linearly from the centre where it is zero, to a maximum at the surface. This, however does not happen with the hexagon, which is not axisymmetric. When the Rover's ARB is twisted, the cross-sections warp or bulge, behaviour that a circular bar does not experience. This exacerbates the problem of the bolts retaining their tension when a stiffer bar of larger diameter is used in place of the original.
Ron.
The bending in the orthogonal planes is why the Polar second moment of area (J) is used to describe the member's resistance to torsion about the longitudinal (z-axis). J is the summation of the second moment of area about the x-axis (Ixx) and the second moment of area about the y-axis (Iyy). Ixx and Iyy describe the member's resistance to bending along each of those planes.
What makes matters more challenging is that a bar with hexagonal cross-section does not behave in the same way that a bar with a circular cross-section does. The latter is axisymmetric; the shear strain varies linearly from the centre where it is zero, to a maximum at the surface. This, however does not happen with the hexagon, which is not axisymmetric. When the Rover's ARB is twisted, the cross-sections warp or bulge, behaviour that a circular bar does not experience. This exacerbates the problem of the bolts retaining their tension when a stiffer bar of larger diameter is used in place of the original.
Ron.
The evidence is, the bolt loosen and this only occurs when using stiffer bars on a track.
Has anyone had the thread pull out of the housing?
I'd suggest that if the threads are not pulled, the bolts are not being torqued enough. Torque them up,
I use Unbrako Socket Head Cap Screws. Reference the Unbrako Engineering Guide for the recommended seat-ing torque, Page 7.
The existing Rover design (which works if std ARB) is levering the clamp apart, just as you'd do to open a casing with a screw driver.
To make things worse the torque the ARB exerts is cyclic. The bolts are under tension then free of load, repeatedly.
Some bolts subject to high cyclic stresses, E.g Big end bolts, are not set to a torque, but torqued to a stretch. One of the reasons for this is to get them well into their elastic stress range and to ensure they are still under stress when the load has changed to a compression load on the joint.
Now to paraphrase the joke; Patient "My arm hurts in three places". Doctor, "Then don't go to those three places."
If this is only occurring when driven on a race track, (probably due to the extra grip causing extra roll and resulting extra stress in the ARB clamp bolts), then just tighten them as you leave the track. But please keep going to the track....
However, if I was to redesign the ARB housing then maybe a fixing that had a close fitting hex that slides over the ARB and is then bolted to the top link. I think this will greatly reduce the stresses the bolts will see.
Has anyone had the thread pull out of the housing?
I'd suggest that if the threads are not pulled, the bolts are not being torqued enough. Torque them up,
I use Unbrako Socket Head Cap Screws. Reference the Unbrako Engineering Guide for the recommended seat-ing torque, Page 7.
The existing Rover design (which works if std ARB) is levering the clamp apart, just as you'd do to open a casing with a screw driver.
To make things worse the torque the ARB exerts is cyclic. The bolts are under tension then free of load, repeatedly.
Some bolts subject to high cyclic stresses, E.g Big end bolts, are not set to a torque, but torqued to a stretch. One of the reasons for this is to get them well into their elastic stress range and to ensure they are still under stress when the load has changed to a compression load on the joint.
Now to paraphrase the joke; Patient "My arm hurts in three places". Doctor, "Then don't go to those three places."
If this is only occurring when driven on a race track, (probably due to the extra grip causing extra roll and resulting extra stress in the ARB clamp bolts), then just tighten them as you leave the track. But please keep going to the track....
However, if I was to redesign the ARB housing then maybe a fixing that had a close fitting hex that slides over the ARB and is then bolted to the top link. I think this will greatly reduce the stresses the bolts will see.
One of mine have come loose, just the once after being there for 12 years so not really a problem. I did have a bolt pull out, but that was because the supplier had sent be the wrong bolts, I think they may have been made out of chocolate, and they just stripped during torquing.
Sparky's winter/spring/summer/autumn work
It would have to be very 'close fitting' and be rendered useless if any play formed at all.
Sparky's winter/spring/summer/autumn work
It would have to be very 'close fitting' and be rendered useless if any play formed at all.
Studs and nuts are often seen as a mechanism for improved connections.
Although not specific to the Rover application, the item below points in the right direction.
Aeroflow Turbo Stud & Nut Kit M10x1.5 | Sparesbox
The primary issue that I can see with your design Gargo is that it does not provide a mechanism to prevent lateral displacement. If you slide one on each end of the ARB, then tighten the retainer, the ARB is still free to move laterally within the retainer. The existing design, although not ideal for track work and larger diameter bars, does prevent lateral movement. You could have some form of retaining plate on the outside that aims to prevent lateral movement, but as Richard indicated, as soon as the faces experience wear, we have another problem.
Ron.
Although not specific to the Rover application, the item below points in the right direction.
Aeroflow Turbo Stud & Nut Kit M10x1.5 | Sparesbox
The primary issue that I can see with your design Gargo is that it does not provide a mechanism to prevent lateral displacement. If you slide one on each end of the ARB, then tighten the retainer, the ARB is still free to move laterally within the retainer. The existing design, although not ideal for track work and larger diameter bars, does prevent lateral movement. You could have some form of retaining plate on the outside that aims to prevent lateral movement, but as Richard indicated, as soon as the faces experience wear, we have another problem.
Ron.
The evidence is, the bolt loosen and this only occurs when using stiffer bars on a track.
Has anyone had the thread pull out of the housing?
I'd suggest that if the threads are not pulled, the bolts are not being torqued enough. Torque them up,
I use Unbrako Socket Head Cap Screws. Reference the Unbrako Engineering Guide for the recommended seat-ing torque, Page 7.
The existing Rover design (which works if std ARB) is levering the clamp apart, just as you'd do to open a casing with a screw driver.
To make things worse the torque the ARB exerts is cyclic. The bolts are under tension then free of load, repeatedly.
Some bolts subject to high cyclic stresses, E.g Big end bolts, are not set to a torque, but torqued to a stretch. One of the reasons for this is to get them well into their elastic stress range and to ensure they are still under stress when the load has changed to a compression load on the joint.
Now to paraphrase the joke; Patient "My arm hurts in three places". Doctor, "Then don't go to those three places."
If this is only occurring when driven on a race track, (probably due to the extra grip causing extra roll and resulting extra stress in the ARB clamp bolts), then just tighten them as you leave the track. But please keep going to the track....
However, if I was to redesign the ARB housing then maybe a fixing that had a close fitting hex that slides over the ARB and is then bolted to the top link. I think this will greatly reduce the stresses the bolts will see.
View attachment 22687
Has anyone had the thread pull out of the housing?
I'd suggest that if the threads are not pulled, the bolts are not being torqued enough. Torque them up,
I use Unbrako Socket Head Cap Screws. Reference the Unbrako Engineering Guide for the recommended seat-ing torque, Page 7.
The existing Rover design (which works if std ARB) is levering the clamp apart, just as you'd do to open a casing with a screw driver.
To make things worse the torque the ARB exerts is cyclic. The bolts are under tension then free of load, repeatedly.
Some bolts subject to high cyclic stresses, E.g Big end bolts, are not set to a torque, but torqued to a stretch. One of the reasons for this is to get them well into their elastic stress range and to ensure they are still under stress when the load has changed to a compression load on the joint.
Now to paraphrase the joke; Patient "My arm hurts in three places". Doctor, "Then don't go to those three places."
If this is only occurring when driven on a race track, (probably due to the extra grip causing extra roll and resulting extra stress in the ARB clamp bolts), then just tighten them as you leave the track. But please keep going to the track....
However, if I was to redesign the ARB housing then maybe a fixing that had a close fitting hex that slides over the ARB and is then bolted to the top link. I think this will greatly reduce the stresses the bolts will see.
View attachment 22687
(1) Having the points of the next top and bottom creates a large stress riser.
(2)Unless you plan to weld or heat shrink it onto the bar ends it’ll be rattle city and will wear loose quite quickly.
I’ve used a slightly higher spec than original torque (+20%) on my setup with blue loctite thread lock. Not had a problem with backing out since then. This includes track time.
Good one. We can leave this then
My suggestion was only a starting point, to reduce the stress in the bolts. Just something that I thought of over toast and coffee this morning. You all make fair points, with a little detail could be overcome.
My suggestion was only a starting point, to reduce the stress in the bolts. Just something that I thought of over toast and coffee this morning. You all make fair points, with a little detail could be overcome.