QuestionQUESTION: Barrie,
I had to pull out my 1954 MG TF distributor last week, a Lucas D2A4, as the shaft bushes were worn enough that the dwell angle and timing is all over the place. I have done a temporary fix by taking a NOS Lucas 45D ( genuine, not Chinese/Indian )with a 12 degree cam and fitted the XPAG gear. It is timed at 11 degrees BTDC static to give around 32 degrees total advance in at 3000 RPM ( 9:1 compression ). The car seems to run well with decent power and no pinging under load. Is it worth fixing the D2A4, or would a correctly set up and re-curved 45D be a better solution. I have a +ve gnd Petronix for the 45D that I have not yet installed.
ANSWER: Hi Paul. If your old D2A4 distributor has worn bushes, then they can be replaced. However, the big problem with the D2A4 is that it is made from two pieces of dis-similar metal. The top part is a cheap alloy and the bottom part is a steel tube. They were cast together and after many cycles of hot and cold they tend to separate. Once this happens the entire body is scrap.
If you want originality, fit a D2A4. If you are not bothered about originality then the 45D4 is a better solution because the body is one piece and replacement parts are readily available. Also, if you want to improve the fuel consumption, then you could fit a 45D4 with a vacuum advance unit.
I have a +ve ground Pertronix in my TF1500 and it has been very reliable for the last 10 years. I recommend them.
I would very much like to know the Lucas part number stamped into your 45D4 distributor. There are many variants, all with different advance curves. It seems that you have found a good one for a mildly tuned XPAG engine. I have found that the best curve is almost a straight line between 10 degrees at 1000 rpm and 33 degrees at 4,500 rpm. If you introduce extra advance at 2,500 to 3,000 rpm then it tends to ping in the mid-range.
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QUESTION: Barrie,
Thanks for the advise.
The distributor is 45D4 41427E 3300 with a 12 degree cam ( I assume, as 12 is stamped on the cam plate ). It came with a vacuum advance 5-13-10.
I removed the vacuum unit, locked the plate and put a blanking plate on the body.
I will send the D2A4 off to Advance Distributor this week for a rebuild and re-curve to your recommendation. I will install it and the Q12 coil only when I take the TF to shows. Once the D2A4 is back I will get the 45D re-curved as per your recommendation with the Pertronix and use that as my driver unit along with a Pertronix coil and modern leads. Should I set the plug gap to 0.035 ? I currently run with Lodge HLN plugs that seem about right.
AnswerHi Paul. My table of Lucas distributors gives the following data:
41427 45D4 9 @ 2000 5/13/10 MG MGB HC
So, you have an MGB distributor for a High Compression MGB, and the vacuum data agrees with your numbers.
However, according to my chart the advance curve peaks at 18 degrees of advance at 4,000 rpm. (The distributor rotates at half the engine speed, hence it says 9@2000). I guess that someone has taken out the 9 and inserted a 12.
You seem to have a very good strategy there.
I set my spark plug gaps at .030 and use a Lucas Sports coil.
Note that one of your carbs has a brass plug in the side, which you can unscrew to reveal a vacuum port. Just drill the brass plug to make a vacuum adapter.
Please check that there is no play in the shaft of your D2A4 distributor body before sending it away for recurving.
