Classic cars forum & vehicle restoration.

[Ray White]

Here is a distributor for a Rolls Royce V8. It clearly has two sets of points. I would like to know how one would set the dwell angles.

[bjacko]

For Dual Point distributors there is a bit more effort involved. You can still set the point gap on the "primary" point set in the distributor (see note below), but you might as well forget the secondary point set at this moment.

NOTE: Primary vs. Secondary (or trailing) point set. The Primary point set is the "first" point to open in relation to the rotation of the engine and it's placement in the distributor housing. If you look into the distributor from the top, you will notice that the pair of points are nested to one side of the distributor housing. No matter the rotation of your distributor, the first point set that opens is called the primary set. The second one that opens is called the secondary (or trailing) point set. When the primary point opens, watch it ... before it closes, the secondary point will open.
To set dual point ignitions you first block the "secondary" point set. You can block it by either not having it in the distributor, or using a thin piece of cardboard such as a matchbook cover between the contacts of the secondary point set. With the same (Safety Precautions) as above: ignition coil wire removed, the cap and rotor off the distributor, and a dwell meter properly connected to the coil, you can spin the engine. The best way to do this is with a remote starter button. The only other way to do this is with someone assisting you. Crank the engine and watch the reading on the dwell meter. You will be setting ONLY the primary point to the required setting at this time.

After you have set the primary point set to the required dwell, install or unblock the secondary point set. You will now spin the engine again and by adjusting ONLY the secondary point set, adjust the the secondary point so that the dwell reading matches the "combined" dwell specification. You do not have to touch the primary set again.

Example: You have a V8 engine application and your dwell settings are 26° (each point), and a combined setting of 33° ± 2°. You will set the primary point to 26° with the secondary set blocked, then by adjusting ONLY the secondary point set, adjust it so the dwell reads 33° (or between 31° and 35°
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1938 Morris 8 Ser II Coupe Utility (Pickup)
1985 Rover SD1 VDP

[Ray White]

Thank you BJ. I could not have asked for a better explanation.

I suppose the correct degrees of dwell setting for any given engine will be found in the instruction manual ... unless there is a way of working it out.?