XK120 jack fix or R&R

(Brian Ternamian) #1

I have one of these Smiths Stevenson jacks and it runs smooth for most of the way, but about 23rds in it binds and is hard to turn. With leverage it is possible, but should not be like this.

Has anyone ever fixed this type of problem OR better yet replaced the screw mechanism in the original body? I have several old screw-type mechanisms that should fit inside the body with some fettling.

The jack seems to be welded and crimped together, but you innovative types out there might have done this with satisfactory result no matter what it wound up looking like. My car will not be concourse or shown to any degree.

If anyone has any or all of this info, please tell me. Thanks

(Gary Grant) #2

Brian, my ‘140 jack was stuck when I got it.
I tried placing it in a tall narrow tin can full of diesel fuel, inverting the jack occasionally to make sure the whole length got immersed.
It came free after a day or so.
Might be worth a try.

(Rob Reilly) #3

I’ve been studying these jacks with a view to reproducing the pre-war type.
So far I have figured out that the screw thread is about 5/32" pitch or 6.4 threads per inch. Assuming it is an ACME thread inside, 6.4 TPI is not a standard ASTM size, but it could be a 4mm pitch in 16mm or 20mm diameter.
To disassemble one in the reverse order that it was assembled, first remove the foot. There are two welds on mine to be cut with a thin cutting wheel, then I think the foot will come out with some persuasion.
Then the outer tube is removed. Cut around, being careful not to cut into the inner tube.
From that point I am guessing, but there must be an ACME threaded insert in the upper end of the inner tube, crimped or welded in.

If you are willing to go that far, post some pictures of your findings.
I of course am not willing to cut into mine.