The big one, drives the alternator of my 72 series 1.
If anyone happens to know I’d be most thankful.
Cheers
cds
Close to 7 inches, using just a tape measure.
I’m curious why you ask.
Rob
Thank you Robert.
I’m calculating rpm speed of a compressor that came to me rather cheaply.
So I’m contemplating using that pulley to maximize
The rpm’s of said compressor at idle.
A good trick, but be sure to consider the max RPM of the compressor and what engine RPM (and road speed) that corresponds to.
Also, IMHO the Series 1 evaporator is the limiting component, not the compressor. The S1 was the first Jaguar car fit with an in-dash (as opposed to boot) evaporator and it is quite small, having been added to the existing heater matrix. Particularly at idle, a second limitation is the condenser (old-fashioned serpentine design, not parallel-flow) and available air flow through it (no electric fan). A third limitation is insufficient air into the cabin, particularly lack of a center vent. These points have all been addressed in the archives.
Hello Robert,
I agree on evaporator core and the condenser,
I have checked out the archives, especially Roger Mabry’s modifications to the existing system with his fan upgrades and additional center vents.
I’ve spent a good amount of time in a 420 with a boot mounted AC unit and
am going that route.
I’ve found this restoration and LS motor swap to be of special interest
I don’t need the LS power, but they are using a trunk mounted AC unit from Manex
http://mxheatcool.com/i-11768070-05-00318-mx-5-floor-mount-evaporator.html
Ideally I will have dual AC front and rear, with the rear doing most of the heavy lifting.
The whole plan is still in its incipient stage right now, but I’ll share when actual action takes place.
The other Robert, thanks again for measuring your pulley
That was my plan, too, although given my energy level it will probably be among my “posthumous” mods. 
Anyway, I got hold of a rear evap unit from a Mark X/420G for the project. In case you are unaware, this unit was fitted to the very earliest XJs. The raised “shelf” at the front of the XJ6 boot (all years) seems to have been designed to fit this unit–it places it to the precise vertical position needed to interface with the intake and blower vents on the rear package shelf.
The front + rear evaporators that we are envisioning form a “split” system similar to that used in various SUVs and limos. If you’ve worked out the details I’d appreciate hearing your thoughts. I’m not sure what signal(s) should be used to cycle the compressor. It may be somewhat autoregulating in that if one evap freezes up, its expansion valve might divert the refrigerant to the other.
I also did a center vent mod similar to that described by Roger–we both like it and recommend it.
What kind of compressor are you considering? The Frigidaire A6 fitted to the 73 (and 72?) is hard to beat with regard to capacity–including at idle.
Feel free to use a real name on this forum if you wish.
I have a rotary Sanden compressor mounted where the old York unit was - just in case your one is similar. Paul
Sorry for the late reply, I intend to use a seltec tm21 which matches the A6 for capacity, and is also a modern design. I’m concerned that the rebuilt a6 and the new aluminum versions still have leak issues from the front and rear seals.
I got a york to sanden block mount system adapter off a 71 I found at pick your parts so the Seltec should fit fine,
I have a spare evaporator housing that I’m going to take apart to see if any modern evaporator will fit.
And then figureing out the plumbing, I want to add a shut off solenoid, but have some issues to look into as far as oil distribution if part of the circuit is shut off
cds (another carl)