20-08-2022, 02:20 PM
Hi
I have dug out an old article by "Andy DeLuvian" (I believe a pen name of Barry Riseley) which appeared in the Austin Seven owners club magazine some considerable time ago. To summarise, for 1937 to 1939 the distributor is a type DK4A with Service Number 405508, later replacements were Service Number 40224/S. In both cases the advance springs set was listed as Service Number 405396/S. In another part of the article it is claimed that both springs were the same.
The advance curve is:
0 deg below 250 RPM
3.5 to 4.5 deg at 1000 RPM
6 to 7.5 deg at 1400 RPM
7 to 8.5 deg at 1800 RPM
By Lucas convention, these are all RPM and degrees at the distributor. At the crankshaft this becomes
0 deg below 500 RPM
7 to 9 deg at 2000 RPM
12 to 15 deg at 2800 RPM
14 to 17 deg at 3600 RPM
Which is not far off a simple straight line, maxing out at about 3100 RPM. To these figures you have to add in the static advance, maybe another 8 crank degrees.
The DK4A model was of course used for other cars, and would have had a different service number and different springs so there are plenty of variants "out there".
All a bit academic really, as fuel has changed, engines are sometimes tuned and advance (within limits) isn't that critical once running.
I have dug out an old article by "Andy DeLuvian" (I believe a pen name of Barry Riseley) which appeared in the Austin Seven owners club magazine some considerable time ago. To summarise, for 1937 to 1939 the distributor is a type DK4A with Service Number 405508, later replacements were Service Number 40224/S. In both cases the advance springs set was listed as Service Number 405396/S. In another part of the article it is claimed that both springs were the same.
The advance curve is:
0 deg below 250 RPM
3.5 to 4.5 deg at 1000 RPM
6 to 7.5 deg at 1400 RPM
7 to 8.5 deg at 1800 RPM
By Lucas convention, these are all RPM and degrees at the distributor. At the crankshaft this becomes
0 deg below 500 RPM
7 to 9 deg at 2000 RPM
12 to 15 deg at 2800 RPM
14 to 17 deg at 3600 RPM
Which is not far off a simple straight line, maxing out at about 3100 RPM. To these figures you have to add in the static advance, maybe another 8 crank degrees.
The DK4A model was of course used for other cars, and would have had a different service number and different springs so there are plenty of variants "out there".
All a bit academic really, as fuel has changed, engines are sometimes tuned and advance (within limits) isn't that critical once running.