This may seem like an insignificant request but that is the level of detail I am at in completing my restoration! does anyone know where I can get the screw that holds the heater control knob onto the rheostat switch?
I measure it at .122" dia. and 42 threads per inch.
Converts to 3.10 mm.
5BA is 3.20 mm and 43 tpi.
So I make it to be a 5BA thread x 3/8" long headless set screw (aka grub screw) with a slot.
You don’t say what country you are in, but in the USA my choice for BA screws is British Tools. They have it.
If you don’t like the cheese head you could cut it off and cut a slot to make it a set screw (grub screw).
The originals were a brass set screw with a slotted head. I broke off half of the slotted head of one of these screws last year. As Rob says it’s probably a No. 5 BA screw. However, I found that a No. 5-40 screw is a good substitute and works fine.
Using a Dreml cut-off wheel, I cut a 5-40 steel screw to the right length, and then cut a slot to make it into a set screw.
It’s a pity that these bakelite knobs wobble abit, even with a tight screw.
Some knobs, and light switch, have a spring fixing, which is far easier to work with when the instr panel is being removed
Thanks for the info guys - much appreciated. For the record I am in the US and did see what may be the correct screw on the Scparts website in the UK but with the shipping etc. did not want to pay that much for a small screw!
The Lucas documentation refers to the following:
Jaguar Switch C.5485 has Lucas code 78262. The Knob fitted to this Fan Switch is Lucas 768473. which has been described as follows.
So Lucas says they use a “Grub Screw” which is a slotted screw without any head (later also with an internal hexagon or Allen key). This grub screw is 5BA (Lucas uses lots of BA threaded screws). I made a new Grub Screw 5BA about 5/16" long with the slot made with a small jigsaw.
5BA measures 0.216" in diameter and has 43 TPI.
In the US other options are No.5 screws with 0.215" and 44 TPI (in UNF format).
See pics.
I’m still having problems uploading pictures in whatever format. I’ve used a very high compression rate and still I’m timed -out with the remark that there was an error during upload and please try again. Anybody?
Bob K.
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Quite right, Mike and Bob, it is indeed a headless set screw (aka grub screw) with a slot.
I should have looked at my car, was looking at a loose knob out of something else.
Bob K. and Rob R. I went back and reviewed the grub screw I made to secure the bakelite knob on the Lucas rheostat. It turns out I used a # 5-40 screw and not a # 6-40 screw to make the grub (or set) screw. I’ve edited my post above to reflect that.
In my parts collection I have spare Lucas rheostats, and note that the little cheese head screws that attach the wires to the terminals are also # 5 BA and screw just as easily into the threaded hole for the bakelite knob as my homemade grub screw made from a # 5-40 screw. (I did not need to force the # 5-40 screw to make it fit.)
It’s true that in the U.S. there are # 5-44 screws that would appear to be a more precise fit. However, that size is a special order item and not typically available at retail hardware stores. I think it would be cheaper to order an individual # 5 BA screw than to order the minimum quantity of # 5-44 screws.
Peder, regarding your comment about the wobbly-fitting bakelite knobs, I agree they seem to have come from the factory that way. It appears the holes in the bakelite knobs were molded too big for the shafts of the rheostat switches. I’m wondering if the solution would be to fill the holes in the knobs with JB Weld (or something similar) and then drill the holes smaller for a precise fit on the shafts.
Ah, that could explain where my cheese head screw came from, and why it was there, somebody thought it would hold the knob better.
If the oversize is at least 0.002", I used an annulus of brass shim stock. It’s unnecessary to drill the shim stock for penetration of the grubscrew BTW. IMHO.
Hello:
I know this is an older topic; I am hoping someone will reply. I have a similar problem with my 1955 XK 140 roadster. I finally found the correct heater replacement knob, but when installing broke the old set screw. Does the XK 140 heater knob use the same size and type of set screw, or something different? Thank you. Gary
Welcome Gary.
The heater switch knob is listed in the XK140 parts book as Lucas 768472, but it should be the same as the Lucas 768473 for XK120, meaning one is a misprint or possibly a little different with the marking, but the screw should be the same.
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