I now know that what I thought was a vacuum advance, is actually a "retard" mechanism....
A British car mechanic has mentioned that it isn't necessary, as long as the distributor is working correctly otherwise.....
Can someone comment on the retard mechanism? Is the mechanic correct? Why
do I care, as this area doesn't inspect for emissions anyway?
Thanks for input.
Edward

 

Not wanting to write a book, and not knowing why it even concerned you. This maybe some good reading to enlighten you on the distributor on your cat.

Vacuum Advance versus Vacuum Retard

Cheers

 

Thank you Gatekeeper...
My retard unit is "blown"....diaphragm is no good, and it looks to be an expensive replacement.
Very interesting article....I'm still not sure if I need the retard mechanism to be working, since vacuum goes down as rpm's increase, I would think that above low speed, there is no real vacuum anyway.....
Looks like more research is needed.
Edward

 

Retard units or other similar trickery with ignition timing is strictly for emission testing purposes. The standards at the time were not that complex and the OEMs found crude, cost effective way to get around them.

The retarded timing does allow the car to pass emissions for that particular test point, but at the expense of performance and fuel consumption or in some cases overheating and poor driveability.

The amount of manifold vacumm does vary with engine speed, but is affected to a greater degree by throttle position. The highest potential vacuum would be created with an engine at red line speed and the throttle suddenly being closed.

It is essential, in addition to the mechanical ignition advance being in good condition, that the vacuum advance work properly. The two work in combination using engine speed and manifold vacuum to give the optimum ignition setting.

 

So the question remains, is there any reason, other than lower emissions, to bother repairing the vacuum retard?
Thanks
Edward

 

A few E-type Gurus lurk on other forums such as Jaglovers forum and E-typeUK . I'm sure you could get an essay regarding your retard concerns there.


Alfred

 

To quote myself: "Retard units or other similar trickery with ignition timing is strictly for emission testing purposes."

So, no.

 

No, vacuum retard is only for emissions, will not help performance. Use the mechanical advance, start about 10 BTDC at idle, make sure it does not exceed about 28 BTDC at high RPM, 4500-5000. I have seen several running without the retard, I have never seen a problem from it.

 

only the late 4.2s had vaccuum retard the ealier cars had vaccuum advance to make distributor advance like a pre smog e type get an old distributor from a pre 67 4.2
you cant just change the advance/retard machanisum as the advance one pulls the points plate in the opposit direction. of course you could opt for an electronic distributor, but the
most economical upgrade is the earlier dist. and Petronics electronic insert, if all of the rest of your dist is good this is as good as the $400. 123 distributors!

 

Thanks for the info....Since I have switched over to triple Webers, and with the Pertronix, the car seems to be working well as is...Webers seem happiest with mechanical advance, anyway. (There is a manifold vacuum nipple, but unused).
Edward

 

Basically, for an XKE-V12, when you set the static ignition timing to the recommended 10-12 deg. BTDC, the greatest "retard" occurs at idle speed where the highest vacuum is generated; at this point, the "retard" readjusts the timing to 4 deg. ATDC where it remains until throttle up. Final adjustments can then be made with the use of a timing light.