The largest and best supported Jaguar cars enthusiast site on the Internet!

Serving Enthusiasts since 1993
The Jag-lovers Web

Currently with 3,166 members

V12 Distributor Cap

V12 Distributor Cap

Alan Howard

Irma Jean Morgan wrote:

My '73 XJ12's distributor cap has two vent nipples; one on the side and one on the top. When I purchased the car I was aware it was running a little rough. Compression was within limits so I figured carbs, spark, or emissions which I thought I could dope out. When I got to the distributor the vent nipple on the side was open. When I took the cap off I was suprised to find that one of the screws stayed in the mount along with a 2"X1/2 inch slice of the cap base.

I went to the Haynes manual and some of my parts catalogs to check prices and now I'm not sure a vented cap is supposed to be fitted to this model year.

  1. Was the wrong cap fitted?
  2. Should the side vent hole be open?
  3. Can you glue a cap together and save the $50.?
  4. Is a cracked cap bound to cause misfires...I can't believe the PO missed it!
  5. I'm in the dark here(token Lucas shot)and would appreciate any help you can offer. Thanks in advance for your time.

The distributor cap fitted to your car is what was fitted to the later HE V12 engines. The idea was to vent the distributor with fresh air to prevent fuel fumes building up inside which can happen under certain circumstances. The result being that when the engine is started the distributor cap literally blows up and usually starts an under-bonnet fire which is very undesirable, dangerous and expensive. The 2 vents on your cap on the HE engines one vent goes to the rh inlet manifold and the other to a filter. Yes you will have to replace the cap you cannot glue them back together as the spark will track to earth along the crack, in fact I am surprised the engine ran with sudh a large broken piece. You should be able to buy an earlier cap without the vents, if you can only buy a vented cap you can either block the vents or try to copy the HE set up.

Please show your support for Jag-lovers by purchasing a set of our Car Stickers and don't forget to tell your friends about them! See our unique scanned collection of Brochures and other memorabilia
from the 1930s onwards! Currently over 260 entries...


Please help support the move to the new site, and DONATE what you can.
A big Thank You to those who have donated already!



Go to our Homepage
Improve your Jag-lovers experience with the Mozilla FireFox Browser!

  View the latest posts from our Forums via an RSS Feed!

Jag-loversTM Ltd / JagWEBTM 1993 - 2023
All rights reserved. Jag-lovers is supported by JagWEBTM
For Terms of Use and General Rules see our Disclaimer
Use of the Jag-lovers logo or trademark name on sites other than Jag-lovers itself in a manner implying endorsement of commercial activities whatsoever is prohibited. Sections of this Web Site may publish members and visitors comments, opinion and photographs/images - Jag-lovers Ltd does not assume or have any responsibility or any liability for members comments or opinions, nor does it claim ownership or copyright of any material that belongs to the original poster including images. The word 'Jaguar' and the leaping cat device, whether used separately or in combination, are registered trademarks and are the property of Jaguar Cars, England. Some images may also be Jaguar Cars. Mirroring or downloading of this site or the publication of material or any extracts therefrom in original or altered form from these pages onto other sites (including reproduction by any other Jaguar enthusiast sites) without express permission violates Jag-lovers Ltd copyright and is prohibited
Go to our Homepage
Your Browser is: CCBot/2.0 (, IP Address logged as on 4th Jun 2023 13:55:12