'48 DeSoto Distributor Questions

[50Traveler]

I have been having trouble with my ‘47 DeSoto being hard to start and hard to keep running at the prescribed rpm. I have been all over the carb and ignition and here is my latest source of confusion.

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When the piston is at TDC and the timing mark is also at TDC, if I set the points to spark at just that moment the rotor is past the number 1 terminal on the distributor cap. If this was the type of distributor where the shaft had a helical gear at the bottom I’d think it was off by one tooth. All this has been checked manually when there is no advance action by either weights or vacuum.

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The car will run sometimes so the spark has to be able to jump the gap from rotor to cap if strong enough. I don’t always get that spark through

In dissecting the distributor I see that the position of the rotor is ultimately determined by the how the distributor shaft is mounted to the bar that the advance weights pivot on. It looks like this area of the shaft is splined and would let me lift and move over one notch for better alignment between rotor and cap.

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Could this have been wrong all this time?

Is the shaft and weight bar OK to separate?

Why are the weight springs so different? I understand that different springs allow for a different degree of advance at different speeds, but the heavier spring seems slack enough to not do anything.

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Any ideas, input, and advice is welcome and very much appreciated

[hchris]

Have you loosened the distributor base clamp and rotated the distributor body whilst still in the block ?

Doing this will alter the rotor to cap position, depending which way you rotate it determines whether the timing is advanced or retarded.

It is highly unlikely that the splined part of the shaft is wrongly positioned and to establish the correct tension of the springs you would need some expensive machinery, it is not unusual to have them loose when the distributor is stationary.

So get the engine started and loosen the clamp bolt, experiment with moving the body in one direction or the other until you get a smooth idle, if it wont start move the body until it does.

Take it out on the road and see if you have any pinging/knocking under acceleration; if so you have it too far advanced, if it overheats then you are retarded. It will take some time so keep perservering.

[Rusty_OToole]

Your engine has a unique feature that makes it easy to find TDC. On the last cylinder there is a pipe plug right above the piston. You can take out this plug and drop a screwdriver down the hole, and feel when the piston reaches TDC. #1 and #6 reach TDC at the same time.

Sometimes the rubber damper in a flywheel pulley fails, allowing the timing mark to shift. You can double check this with the method described above.

The different springs are selected to give the correct advance characteristics. It appears the light spring allows quick advance as soon as the engine starts, then it advances more slowly as the engine speeds up.

[Guest Silverghost]

If you adjusted the ignition points to break-open after the #1 cap tower you might be setting the ign timing incorrectly !

Try setting it slightly Before this point or exactly at the # 1 tower. (you may be setting ign timing in the wrong direction !

You should really get a timing light to do this properly ! Good timing lights are worth the money !

Why not rotate the didtributor while engine is running and set it at highest engine idle then test drive and go from this point as mentioned in post above ?

The advance springs sound like they are the correct type .

Slack in one spring is normal for the reasons mentioned !

The slack is there for a reason !

Is the vacuum advance working ?

You should also check it's operation.

Make sure mechanical advance weights are also free to move properly.

Are your points properly gapped ? Point gap also effects engine timing !

This should be an easy fix !

Good Luck !

Let us know what you find ?