Having a bit of a challenge! The cap currently on the distributor appears to be an original Lucas part #407043. I ordered replacement caps from both Moss Motors and British Parts NW in the US and in both cases received a new cap #2927 that supposedly is a direct replacement for the 407403 cap. In both cases this was NOT the case!

If I line up the 4 locating squared off slots in the two caps, the newer cap semicircular mounting notch is not properly aligned. Essentially it will NOT fit the car!

I posted a poor 2 minute video of this issue here.

Anyone else seen this issue/have a solution/source for a correct cap?

Rick

 

[Having a bit of a challenge! The cap currently on the distributor appears to be an original Lucas part #407043.

Reply:



I bought a cap this year and it is on the car and running. I didn’t check the clocking of all the notches since it fit. Moss part 2927.

My car is an XK120 1953; been in my family since 1954. Hasn’t been really been modified at all.

Maybe try Anglo Parts : 081.714/5/6 ?

 

Well research is the key!! Here's what I have found out...
“There are at least three outer bodies and three Bakelite caps”.The interesting bit is that knowing the distributor number (in this case DVX6A) is only part of the challenge.

On the XK120, based on point gap and static timing, the distributor upper body is additionally numbered with a second number after the “D” number (D for dual overhead cam) that start with 40***. In this case, again, the next series of number is 40199E indicating point gap of .014-.016 and a static timing of 7 degrees.

Hence not all caps fit all XK120’s. The Cap originally internally numbered 407043 is specific to DVX6A Distributor with Body number 40199D or E and maybe 40199A.

WOW! Those Jag engineers got very specific on caps without any understanding of the laments of owners many number of years later trying to find the correct cap for their car, aka aftermarket manufacturing!.

Bottom line, the quest to find the correct cap is not simply based on the number on the OLD cap unless you're acquiring NOS and vendors basing their fitment on the OLD cap number only or the Distributor body only without the additional stamping information for the gap and timing are probably going to provide you with a "GENERIC" part that may NOT fit.

My experience is that 3 vendors provided caps did exactly the above and until I found a NOS dizzy cap, my only other choice would to have been to modify the generic cap by enlarging the locating tabs to make the cap fit the body of the distributor of the car (leaving room for error and more opening for water/oil entering the distributor body.

Rick Mathis