The advantages of vacuum advance distributors are well known and I have struggled to work out how to modify the standard TA distributor, eventually giving up. However John Saunders’ article in the May Octagon Bulletin rejuvenated my efforts, this time using a modern distributor.
I scrounged a Metro A + Points Distributor (Lucas model 59D4). The advantage of this type is its neat vacuum unit and a wide flange to which a clamp can locate.
The standard drive dog is replaced with the drive gear. I reused the roll pin which is too long and needs filing flush to miss the camshaft gear. There was not enough clearance to reuse the thrust washer so I left it out. I also ran some Loctite 290 into the joint to stop any gear wobble.
The photo shows two mounting clamps, one using a pop rivet to hold the jubilee clip to its tab. The other, the tab folds over the jubilee clip, a piece of rubber locating it. Both work fine as there is no need for great force to hold the distributor still. Just nip up the clip. Make a new short tab bolt.
Showing mounting clamps in position
The vacuum take off is via a hole (1mm ish) drilled through the air cleaner mounting bolt and into the inlet manifold. This needs to seal from leaks so I used some soft washers and goo. I drilled the head of the bolt (3/16 diameter and 3/16 deep ish) and glued a small metal tube for the take off pipe.
Showing the vacuum take off point
Distributors come with various centrifugal and vacuum advance curves; I need to do more research on these. However in the meantime I have set my TA to 5 degrees btdc, vacuum disconnected, at 700 rpm, strobe. The vacuum adds more tick over advance up to about 20 degrees (about 20 inch on my vacuum gauge).
John Saunders has done much work on the subject, which gives us valuable information.
Ed’s note: This article was sent to me by David Heath. The next is also penned by David.