TC Distributor Rebuild

[Mark Jablonski]

After two botched attempts by some professionals, I'm going to have a crack at rebuilding my TC's DKY4A distributor. I'm hoping that someone can help me with the following questions:

1. What is the maximum recommended total advance for an XPAG with about 8.9:1 CR and running 98 octane fuel? (I calculated the CR to be 8.7:1 without any crushing of the head gasket and 8.9:1 with the gasket crushed to 50%.)
2. What is the correct location of the drive gear with respect to the distributor body? The distributor has the advance/retard micrometer. Is the gear location critical or is there some leeway?
3. On the rebuilt distributor, between the drive gear and the body, I have a fibre washer sandwiched between two shims. What is the reason for the fibre washer?
4. There is a fibre washer underneath the advance plate. I have a few shafts and advance plates but all have these washers quite worn or missing. I'm assuming that it is possible to replace this washer and that it's just a press fit on the pips next to the shaft, under the plate. I imagine that this could be replaced by a bronze washer, which should last much longer than a fibre washer. Or, is there a reason for using fibre? If it has to be fibre, can a standard red fibre washer be used?
5. The people who rebuilt the distributor fitted cast iron bushes. I understand that the original Lucas ones were bronze. Is there a significant disadvantage in leaving the CI bushes in situ?
6. In choosing springs for the advance mechanism, I've seen equal springs fitted (which, as revs rise, would give a steady increase in advance until the limit of the advance plate was reached) as well as unequal springs with a light spring acting first then at a certain point a heavier spring coming into play (giving a two stage increase in advance, steep at first followed by a shallower gradient). Which is preferred?
7. Is there anything else that I need to be aware of?
Thanks in advance.


Mark Jablonski
Melbourne Australia

[Duncan M]

There is brief mention of a 1/8" spacer in this article from this site, under the DKY4A distributor. And other info about spacing. http://www.mg-tabc.org/library/distributor.htm

The two different springs allow the one spring to operate the advance at lower engine speeds, then when the advance goes past the useful range of that spring, the second and (at rest) more relaxed spring is going into action to give an overall smoother operation of the advance plate. I am pretty sure the TC had the two different springs, and that is also the preferred way. I am using stock advance, and found new springs at Abingdon Spares here in the U.S. That is about all I can answer with confidence. An interesting brief read here-
http://www.mgccsa.org.au/Front%20Page%2 ... 20Type.pdf
but cannot get the whole address link to load here. It mentions TC and early TD with high compression cannot use the D2A4 dist. and to "use 40162 and fit 407248/S auto advance springs." Mention of AEG122 camshaft.
Duncan-

[Mark Jablonski]

Thanks Duncan the reason for my question re springs is that I've seen both types sold as suitable for a TC. I'm inclined to agree with you that unequal springs is the way to go. Thanks for the link to the article, it answers most of my questions. I shouldn't have been so lazy and ought to have looked through the tech pages before I submitted my post.

Cheers

Mark