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MG MGB Technical - Correct starting location of Vacuum Advance

After replacing the SU’s with a Weber on my 72 B roadster, I checked out the distributor and other ancillary components only to find out that the vacuum advance is shot. In preparation for replacement, I removed all the parts I could to the distributor and cleaned it thoroughly.
When it comes time to re-install the vacuum advance, where is a good starting location for the calibration wheel at the end of the vacuum advance? I haven’t ever noticed this in any literature and like everything else, if I have to start somewhere; I could be totally in the wrong direction if I’m not careful.
Also, should I use any grease on the underside of the advance plate where the two parts make contact? I thought some electrical grease might do the trick, if that sounds good to anyone else.
Cleve

Cleve. Generally, the vacuum advance's vernier adjustment is set one half way through its travel to allow the maximum amount of adjustment in either direction. In truth, it no longer really matters. The vernier adjustment feature was a hold over from the early days of automobiles and varying qualities of fuel. There was a reason that Lucas did not bother to incorporate such a feature after the 25D series distributors--it had been obsolete for many years by then.

But, when the old vacuum advance unit was removed it affected the basic ignition timing of the engine, which should have been checked and reset back to the proper specification for your engine. When the new vacuum advance is installed, it will, again, cause a change in the timing and you will have to readjust the timing to the correct specification.

Les
Les Bengtson

Thanks Les! I can always count on you to give clear and sound information!
What about the question regarding grease? Should I lube the advance plates, or let the plastic bits do the sliding?
Cleve

Cleve. On the bearing areas between the two pieces which form the points plate, I use a slight amount of grease. I generally use something called "Super Lube" which is a teflon grease I have found to work quite well in a number of applications over the years.

But, I have never found any source for factory recommendations as to lubricants to use (other than some oil, once a year, in the workshop manual) and live in the desert. I do not know how much, if any, effect that climate may have on the required lubrication.

By best advise is to try it, use the grease sparingly, and observe what happens. If you perceive a problem, clean off the grease and see if that has any effect on the perceived problem.

Les
Les Bengtson

Original plates had a smear of grease at each plastic button contact zone - looked just like the grease on the points cam. I use Lubriplate. Also the same grease or oil on the center spigot where the top plate turns on the lower one, and oil in the hole in the shaft under the rotor - 3 drops every 3000 miles. But then your distributor never wears out...

FRM
FR Millmore

Indeed, start off in the middle. But in fact it has come back into use again since the demise of 4-star leaded and only intermittent availability of 97, 98 or 99 octane especially in some parts of the UK. One could always detune it to run on 95 all the time, but where's the fun in that? Note this is nothing to do with whether you have an unleaded head or not.
Paul Hunt

This thread was discussed between 07/07/2009 and 08/07/2009

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