31 PA Timing Service and Vacuum Retard System adjustments

[Bill James]

To answer Jim's ? about service bulletins, I was hoping someone would jump in. All the information I have on the PA came from this site, and what I could find on e-bay. Of course this site is a gold mine of info, just keep looking! Bill James

[David Rainville]

Bill James reply is right on, I'm having the same problem. I wish someone would come up with a correct procedure for setting the vacuum unit.

[p4jim]

I will soon be working on the timing of my 30U.  Where can the service bulletins be found?  thanks, jim

[Bill James]

I'll try again on the pictures, Bill James

[Bill James]

So here goes, I'm still trying to learn the right way to time my beloved model PA. I talked to an old owner some time back, he told me if a guy could learn to adjust the vacumn advance properly, you could stand back and count the strokes. I'm a long way from there!
After all the great information from you guys, I'm going to try and list what I know, what I don't know, and what I assume. I will also try and include a couple pictures showing what the vacumn advance looks like and a picture of the beast as it sets at idle.
To start with the PA does not have a vibration dampner at the front of the engine, just a belt pulley with no timing marks. The model PB does not either, but it does have a timing mark on the flywheel with an access hole and a timing pointer. I just learned this wonderful info today when I dug a 1932 PA flywheel and bell housing out of my parts supply (junk?) scraped the grease off, and there it was! Shoulda used that flywheel and bell housing when I put my PA together, Huh?
I have a copy of a Plymouth Mechanics' Repair Manual and it seems the PA just falls through the cracks when it comes to good instructions. It shows the 1931 PA has either a manual or an automatic spark advance. This is my assumption as it shows a 22 degree spark advance for the manual and 18 degrees for the automatic. Then it goes on to say to time the ignition with no 1 cyl. .046" before TDC on the comp. stroke and the spark lever in the the full retard position. doesn't say anything about a vacumn advance, then goes ahead and explains how to time the 1932 PB. By the way, then I read where you time 1929 U in the fully advanced position. Nooo, I'm not confused!
This vacumn advance is like no other I've seen, it has a wire that conects to the lever, or arm, on the distributor plate, with a small clamp and screw, so the thing could be adjusted. I turned the plate from stop to stop and it seems about 18 degrees as above. So I adjust it all the way to the stop in the retard position and clamp everthing down. The engine is very hard to start, seem like its trying to start with the ignition advanced. When it starts,of course the vacumn turns the distributor to the advanced position, and the engine runs rough. Sooo I fiddle with it trying to hit a happy medium where it starts easy, and runs smooth. I've never got it right where I want it, good enough to drive but I would like it better.
Well, I'll keep on fiddeling with it, it's fun and it keeps me out of the bars! Thanks to everone for your help, and have MERRY CHRISTMAS. Bill James

[ehenin]

For your enjoyment I am posting Service Bulletin 438CH on the 31PA and the Vacuum Spark Control information
First:
The vacuum spark control unit is used to provide an earlier spark for part throttle operation and automatically retard the spark for full throttle operation.  This unit is fully automatic and cannot be adjusted.  It is correctly calibrated at the factory and should not be tampered with.
How to Test the Vacuum Spark Control:  If the vacuum spark control does not operate properly, it can be tested with a neon engine timing light.
1. Connect the light in series with No. 1 spark plug and start the engine.
2. With the engine running at slow idle speed, hold the neon light near the vibration neutralizer so that the neon flashes and the marks on the neutralizer can be observed at the same time.  Carefully observe the position of the marks on the neutralizer with relation to the pointer at the time the neon flashes occur.  The neutralizer should be in the timing position each time a flash occurs.
3. Open the throttle wide and observe the change in the time of the neon flashes.  If the vacuum control unit is functioning properly, the change in the time of the neon flashes should be approximately 11 degrees on the neutralizer.
4. Close the throttle until the engine is operating at a speed equivalent to approximately 25 miles per hour.  As this change in throttle position occurs, the neon flashes should advance approximately 10 to 11 degrees.  This amount of advance will depend upon the vacuum created in the intake manifold.
Should it be found that the vacuum control unit is inoperative or does not function properly, disconnect the vacuum line at the unit and connect a vacuum gauge into the line.  If the maximum vacuum created at this point is less than 14?, inspect the vacuum line and ducts in the carburetor for stoppage.  Should this vacuum test show a vacuum reading or 14? or more, the vacuum control unit will be found to be defective and the compete assembly should be replaced with a new unit.

Second: The timing Service Bulletin:
September 4th, 1931
Service Bulletin No. 438-CH
Engine Tuning Plymouth (Code PA)
To All Chrysler Distributors and Dealers:
Your particular attention is called to the necessity of accurate engine tuning for satisfactory performance of the new Plymouth with Floating Power.  While it is true that all engines should be properly tuned, we want to emphasize the points which have a direct bearing upon the degree of owner satisfaction achieved.

Tuning operations must be thorough.  For you convenience, these operations are listed below:
1. Remove all spark plugs, inspect for cracked porcelains or paint and set points with gauge to exactly .022?.
2. Inspect all high tension wires for possible fractures and tighten connections.
3. Reset ignition timing to .046 before top dead center.  A timing gauge must be used for this purpose.
4. Clean and adjust breaker points with gauge to exactly .020?.
5. Clean distributor contacts and rotor and inspect cap for possible cracks.
6. Check operation of vacuum controlled spark retard.  Remove dirt or paint that may interfere with operation.
7. Check water level in battery and clean terminal and ground connections.
8. Adjust idling speed of engine to six (6) miles per hour in high gear.
9. Change idle adjustment of carburetor for smooth engine operation preferable to the lean side.
10. Adjust accelerator pump by-pass screw to 1 ? turns for summer operation.  About ? turn is required for cold weather.
11. Clean out fuel filter and screens and open up gas tank vent.
12. Tighten carburetor to manifold and manifold to cylinder block. Check for leaks.
13. Adjust intake tappets with gauge to .005? minimum when engine is hot.
Adjust exhaust tappets to .007?.
14. Any evidence of improperly seating valves should be corrected.

It must be borne in mind that accurate engine tuning is of greater importance than ever before.  Therefore, these instructions should be followed by your Service Department whenever the occasion arises.