Packard Forum Index » Post-War (1946-54)

My car is a 47 Clipper 2106. I have the Packard Tune up bulletin. In it, they are using a Sun type machine for setting up the engine. I do not have a Sun machine!

Question : should the vacuum line be disconnected and plugged when reading the dwell angle? There is no mention of this in the bulletin. The points were carefully set and the engine runs beautifully. However, the dwell is about 20 degrees at 800 RPM--with the vacuum line connected. It does increase to 27 degrees with engine RPM--Which makes sense if the vacuum advance is working. So, what is the best procedure?

Am I missing something? I don't see how a change in timing via vacuum advance should alter dwell angle unless the vacuum unit is inadvertently "cocking" the moveable breaker plate and thus altering the point gap.

I suggest you take your distributor apart and examine the interplay between the fixed and moveable breaker plates. The should alter position with application of vacuum and hence alter timing but the moveable plate should not lift and change gap and hence dwell. I'm assuming your distributor is an Autolite which uses a very elegant ring ball bearing to connect the plates - Delco units not so elegant. If you have slop, press the plates apart, examine the bearing which probably requires fresh light grease like Lubriplate.

I'd like some clarification too as to how others do timing. Most mechanics I have watched seem to use the vac advance disconnected and line plugged method when setting the initial timing.

In the ignition systems training manual there is a statement in a line by itself to have the vacuum line tightened. Since they are discussing timing am assuming that means the vac advance line to dist. They go on to the procedure for doing a static setting with the engine not running by using a test light and setting the dist so the light just goes out as the points open at the chart recommended value (6 btdc for a 2106). A paragraph or so later it goes into using the neon timing light with engine running and also setting the dist at the chart value for the engine.

Question in my mind is what am I missing. How can both be correct when no vacuum would be present when setting static with engine not running and the test light yet the same degree mark is used with neon light and engine running. Presumably the vacuum advance is at full advance with the 18" or so idle vacuum so wouldn't the desired values be different?

The only caution Packard has about advances when setting timing is to make sure the engine is below a certain RPM so the centrifugal advance doesn't come into play. Haven't found a mention in the training manual or any SM of doing something with the vacuum.

My understanding is that whether or not to disconnect the vacuum unit for timing depends on whether the vacuum port in the carburetor throat is above or below the throttle plate when it is in the closed position.

I guess that would make sense but no matter the port location one would think there is some vacuum present either place when the engine is running. Perhaps not enough to make the advance work if the port is above the throttle plate at idle is the thinking.

I seem to recall a discussion 2-3 years ago where there were some recommendations to remove the advance from the carb and pipe it from the intake manifold. IIRC some did it because it was thought that was a more responsive to true engine condition location and would help with some symptoms others were having (running hot maybe??)

Still curious what the majority do.

IIRC some did it because it was thought that was a more responsive to true engine condition location

Pretty hard to buy into that which essentially says that a half a century of automotive engineers world wide that dealt with engine management systems like ignition just "got it wrong".

Rscott77x
The information in this reply was based on a 1954 issue of the 'Motor's Auto Repair Manual'. In the 'tune-up' section is a statement that the vacuum advance "is connected through a vacuum line to the carburetor above the throttle plate so that idling performance will not be affected." The italicized emphasis on the word 'above' is a direct quote from the manual. There is a diagram showing the details of the location of the carburetor vacuum port in the 'tune-up' section, however in the carburetor section I cannot find a diagram specific to a Carter two or four barrel carburetor that shows the location of the port.
In the Packard specific section of the manual there are tables that present the amount of vacuum to initiate vacuum chamber motion, and likewise the vacuum and angular defection at the end of the chamber's stroke. For the post-war Packard's the chamber will require 5-7 inhg to initiate motion, and 11-19 inhg for a full stroke. While I've quoted ranges of performance each distributor type and engine configuration has a separate line of data of the expected performance of the vacuum chamber. The specifications for the centrifugal advance suggest that that this system will also not be active at normal idle speeds. The data is tabulated as a function of distributor speed, so the reader is cautioned to convert to engine speed if the timing is being checked while the distributor is installed in the engine.
I believe if the idle speed is correctly adjusted the throttle blade will be below the vacuum advance port and the vacuum at that port will be too low to activate the chamber. Likewise if the idle speed is correctly adjusted the centrifugal advance is also not be active. Therefore I've concluded that the timing specification is for static timing only, and there is no need to disconnect the vacuum line to the chamber while adjusting the ignition timing . . . remember the idle speed must be within specification and changing the static timing may alter that speed.
As a practicable matter I disconnect the vacuum line to set the timing. Once the static timing is set I observe the centrifugal advance by increasing the engine speed, and then with a small handheld vacuum pump observe the vacuum advance. For Autolite distributors the mere motion of the distributor housing is enough to confirm functionality of the vacuum advance and the vacuum pump is not required.
With respect to the dwell angle changing with engine RPM; I'm at a complete loss on that one. If you have another car with a breaker point ignition I would install the meter and get a second data set. The manual tabulates that the 'cam angle' (aka dwell) for your car is 27-30 degrees, with an idle speed of 375 RPM.
Dp

With respect to the dwell angle changing with engine RPM; I'm at a complete loss on that one.

Just to repeat, the only times I seen this, the cause was failure of the mechanisms that control the motion of the moveable breaker plate relative to the fixed plate. I again suggest you take a good close look at this.

I agree with OD on the dwell meter symptom. I was offering the idea of a second sample as a means to exonerate the instrument.

I agree with OD on the dwell meter symptom. I was offering the idea of a second sample as a means to exonerate the instrument.