Aftermarket steering arms and ball joint tapers (2017 thread)

A Facebook post said some Elise Parts steering arms had the wrong taper. An owner who runs their anti-bump-steer kit asked which arms, which joints and which taper were affected. The thread sorted out two kinds of arm:

• The anti-bump-steer arm kit is made for rose-jointed (bolt-through) track rod ends. Its end has a simple parallel hole, with no taper there. The kit comes with the rose-jointed ends, bolts, spacers and nuts.
• The other arm takes standard tapered track rod ends, so it has a taper for the track rod end as well as a taper for the upper wishbone ball joint.

What was reported:

• A poster from Spitfire Engineering said they have an arm where the track rod end taper was supplied with the wrong angle and the wrong depth, so the ball joint "cut a new taper" into the soft material and kept working loose until retightened. The wishbone ball joint taper was also set 4 mm too shallow, leaving much of the ball joint taper outside the arm and unsupported. Under hard braking the same forces can shear the two bolts, which he linked to the Lotus bulletin upgrading them to 10.9 grade. He said most of the expanding taper, up to the widest part of the ball joint, should be inside the arm and not visible. He noted that the original arms are steel, with a section 11.8 mm thick at the rack pick-up.
• An owner posted a video of an original (tapered) track rod end moving about in one of these arms. He said it isn't the bolt-through version, so the arm is the tapered type. He added that a separate problem is ball joints sold with the wrong taper, which he has seen on old ones and been supplied: they have a bigger diameter at the small and large ends, so the angle is wrong as well.
• Other owners had no trouble. One fitted the standard version of these arms with Elise Parts ball joints and original arms, and had no problem. One with the bolt-through kit found his ball joints needed a splitter to remove, so they weren't loose, and the originals hadn't pulled out, though the ball joint sat 1 to 2 mm proud of the arm. Another found his wishbone ball joint looked seated but the thread barely showed beyond the Nyloc nut, though he had done several track days with no play.
• One owner thought the Elise Parts joints are original spec. Nobody in the thread had measured the taper dimensions.

What owners said to check:

• Which arm you have. Rose-joint arms use a bolt through a plain hole. Only the other arm has a taper for the track rod end.
• How much thread shows. One owner said to look at how much thread sticks out of the bottom, whether any taper shows at the top, and, with the nut off, whether there is crushing damage on the top of the arm or hub carrier where the taper has been pressed in.
• How far in the taper sits. Push the rubber boot back and look between the joint and the arm. The widest part of the taper should be close to the surface of the arm, as on the original. On the arms the Spitfire poster had, it was several millimetres away.
• Check the rest of the ball joints too, including that they sit correctly in the original hub carriers, if you have any with a wrong taper.
• Undo the nut and see whether the ball joint simply falls out, if you want to be sure. Fit new Nyloc nuts when you reassemble.
• One owner fitted new bolts as a precaution when he checked his. See Front wishbone removal for the wishbone side.