Restoring the Advance Curve

I just bought my 1953 MG TD in Great Britain a few months ago. The engine was performing at best when I was in the original cool climate of the make. But arriving in Toulouse, South of France, I noticed the engine was dangerously knocking at high revs; maybe due to being in a climate with much higher temperatures?

I discovered that the distributor was the faulty part. The secondary spring of the advance plate was always loose even at maximum advance. And the root cause was the toggle that was worn where the spring catches. This was easy to diagnose because the hole is much more a slot. The other end of the slot has never been used and clearly shows the initial size. A few tenth of millimetre is enough to alter the advance curve. This kind of wear can only lead to more advance than originally.

The solution was quite easy. I made a plug out of a brass plate that exactly fits the long hole of the toggle, ‘tin welded’ it inside and drilled a 1.5mm hole. I chose to drill it next to the centre and further adjust the position with a rats tail file. The position was adjusted so as the spring action just begins at 7 degrees advance according to 40367 advance curve. The distributor on the workbench, this was measured with a protractor and with only one weight fitted on the advance plate.

The picture above shows, from right to left, the little bronze plug, the toggle which is worn on the left side, and the final assembly drilled and file adjusted. The other toggle was also worn but not so much. The primary spring hole was then adjusted to initiate tension of the spring at 0 degrees advance. This position would probably need a strobe lamp for precision. 0 Euros, a few hours and the car does not ‘pink’ anymore.

Laurent, France

Ed’s note: The TD in question is TD29133 which was mentioned in the previous issue of TTT 2 in connection with some gaps in its history.