XK120 steering idler

Is the idler different for RHD and LHD? Apart from the main bush, what else wears? I assume that the thread bearing at the top wears more quickly in the bronze (brass?) top than the threads on the steel shaft…? If the top housing wears, what do you do then??
Chris

LHD and RHD are different housings, opposite hands.
However, Mark V uses the same two housings, so other than the lever arm itself, which is at a different angle on a Mark V, all other parts of a LHD Mark V idler are the same as a LHD XK120, and likewise with RHD cars.
Mark VII did not use this design.
If the main bush wore out you might see wear on the steel shaft.
The threads in the top of the housing are steel. They are not screwed in tight, need to be able to turn about 90 degrees in service operation.



If nobody puts oil in the housing for a few decades, the threads will rust together so the shaft won’t turn, and then the idler arm will work loose at the taper and turn on the shaft.
Then a few decades later somebody will buy what’s left of that car for parts and discover this, and spend 4 hours heating with a torch and cooling and oiling it until the threads loosen up. Guess who. :grin:

Look also to see if there’s a crack at the lower bolt hole flange. If the car has hit a bad pot hole or curb in the past this is a common failure point.

…and then when the threads loosened, the bushing screwed out of the body with the shaft, the two bound together by congealed oil.

Ha, ha! That’s one way to get the bushing out. :laughing:

I had thought that the thread for the top of the shaft was in the brass cover cap, but it now seems more likely to me that the thread is formed in the top of the body casting itself… true?? Can’t quite see that in your photos, Rob. I was told that the shaft was moving up and down a bit when the wheel was turned, which suggests some wear in either the thread in the body or the shaft (hopefully more in the shaft than the body!)
I haven’t yet investigated it myself, but the best solution would seem to be to get another RHD idler and rebuild it with new shaft, bush and seal, so I can then put it straight onto the car.

Sorry my explanation was not clear; I assumed you already knew how it works.
There are threads in the top of the housing, and the threads on the shaft are screwed into these, but not tight. The thread is 11/16-11 BSW for a pitch of .091 inches. The shaft does indeed move up and down a little bit in the threads with the normal turning motion. I don’t know the arc the arm moves, but assuming 90 degrees, that would be .023 inches or 0.58 mm.
The threads in the brass cap are for the filler plug.
What is wrong with yours that brought up this question?

Thanks, Rob. That’s clear to me now. I was told that the arm on the idler was seen to move up and down when the steering wheel was rocked from side to side, but I haven’t checked it for myself yet. It could be wear in the threads or it could be that the shaft has seized and the arm has been working loose on the taper, as some have experienced. I hope it’s not that!
I stupidly mistook the threads in the top cover as the ones that would register with the shaft threads, forgetting that there had to be a thread for the filler plug! I read that 140 weight oil should be used, but if the bottom seal is doing its job, it should hardly ever need topping up, should it?

SAE 140 viscosity is correct, same as the steering box. In real life seals are never perfect, so for all of you 120 owners, don’t ignore this lever.

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