I'd've thunk it's clamping over the greatest possible area just as it is in yer pic. !!!
How are you gonna 'space that out' and still have the half hex shaped clamping faces grip the bar?
Ain't no room for washers, is there?
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.
Talking of the uprated ARB clamps & bolts, l'm still suspecting that it would be best to space these gaps between the clamps out rather than leaving the centre of the bolts free to take all of the twisting force. Is that a reasonable assumption?
View attachment 22664
Which is pretty close to the standard setup. I believe it’s in the region of 2x the diameter. I’m using grade 8 UNFs as per original threads.The depth of thread engagement needs to be at least 1 to 1.5 times the bolt diameter. Less than that, and there is a risk of joint failure, in one form or another.
Ron
"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
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 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?
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
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.
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
Good one. We can leave this thenI’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.
If you wanted a collet style clamp I would rotate the hex 90° (as it was originally) and put a slot on one side so you can still use it as a clamp. That would optimise surface area and structure equally.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.