30U

[FourDoor]

This information is worth it's weight in gold. This question has come up several times about the '31 PA vaccuum retard system and this is the definitive answer. Could it be reposted with " '31 PA VACCUUM RETARD SYSTEM ADJUST INFO" as a heading so a search can always be done on site.     

[ehenin]

I found this in a Plymouth Mechanics manual:
Vacuum Spark Control
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.
Eric

[chetbrz]

Chet, thats a great info sheet on ignition timing for the 1929 U. I just wish I could locate the same info for the 1931 PA. The part that has me stumped is adjustment of the "new" vacumn advance ???

Bill,? ?Tks for the At-A-Boy, sorry but I can't help you with the Vacuum Advance Adj.??

Chet..

[ehenin]

Bill,
I have Chrysler Service Bulletin 438-CH dated September 4, 1931.?
For the PA Engine Tuning vacuum controlled spark retard it only says to
"Check operation of vacuum controlled spark retard.? Remove dirt or paint that may interfere with operation."
There is no mention of adjustment for the spark retard.
Eric

[p4jim]

Tod, thanks.  It is a big help for me to have the "why" answered.  jim

[TodFitch]

In a sliding gear transmission each you connect the output shaft of the transmission through one of several gears which are driven at different speeds (forward) and possibly different directions (reverse gear). If you want to shift into a particular gear then you want that gear and the output shaft to be spinning at the same speed so that the relative motions of their gear teeth is small. Otherwise you get grinding.

Originally they actually had square cut gears that slid back and forth on the output shaft. This allows you no option but to "double clutch". That is, pause the shifting in neutral and then either wait for the gears to slow down due to friction in the transmission (up shifting) or blipping the throttle to speed up the counter shaft. In either case you are trying to get the counter shaft gear teeth to be going the same speed as the teeth on the sliding gear.

By 1933 they had replaced the sliding square cut gears with helical cut gears to be quieter. And instead of sliding the output shaft gears they had a sliding "dog clutch" to make it less critical that the speeds match exactly.

Not sure when it was for Plymouth (1935 or 1936 or 1937) but the next and final step was to put a lock out mechanism and synchronizing mechanism into the sliding dog clutch. That is a fully synchronized transmission. Basically there is a lock out pin or tab that keeps the sliding dog from engaging unless its speed matches the gear on the output shaft. And there is a clutch/friction mechanism so that the speed of the sliding unit and the gear will match their speeds. And with that the need for double clutching disappeared. Unless your synchronizers wear out. :)

On my 1933 I find that running heavy duty gear lube helps me on the up shifts. What also helps is shifting at a relatively slow speed. With the low end torque you probably ought to be in high gear by 20 MPH or so.

For down shifting, all I can say is it takes practice. :) And if you haven't driven the car in a while you will get out of practice. :(

[p4jim]

What is the reason for double clutching?? ? Here is my understanding.? Shift from first gear to neutral,? release clutch, depress clutch shift to second gear, release clutch.? ? ?What happens in the transmission to make the gears mesh properly??

Perhaps my timing is messed up.? Should the time spent in neutral be over a moment or does it vary?

Don't you just love us newbies? :<)

Thanks for all this help !!!!? ?jim gray, san jose, ca

[Bill James]

Chet, thats a great info sheet on ignition timing for the 1929 U. I just wish I could locate the same info for the 1931 PA. The part that has me stumped is adjustment of the "new" vacumn advance ???

[36 Ply]

Jim-

I'm guessing that, due to what year your? 30U was built, that double-clutching would be best, especially for downshifting.

Best of luck when you visit the CHP.

Regards,

Pat O'Connor

[p4jim]

Patrick the 30U is an ebay car from Pennsylvana.? It got there from Texas.? It was sold to me by Ray Killiany of Jermyn, Pa.? ?It was stored for quite a while and had the usual problems.? Non-working brake cylinders, rust in gas tank, timing way off, rust in coolant, leaking water pump.? Thursday it goes to the Calif highway patrol for a VIN check so it can get a Ca. license.? ?

Thanks for the driving story.? Since my 50mph drive we have been up to 40 but while it runs better it has a way to go.? I realized today that the spark control does not hold the distributer at full advance and it gets slugish until given a push in.? It drips fuel from the carb when shut off.? (it did spill gas on the exhaust pipe do to a bad gasket on the fuel level sender)? It also has good days and bad but I'm blaming the bad on the spark retard for now.? Once it is licensed I'd like to find out if the carb is working properly, the original goal was to get it driveable for the chp at the least expense.

What is the proper way to shift her?? Sometime its all smooth sometimes its a tad embarrassing.

I'll give it another five gallons tomorrow and see if it helps.

Thanks, jim

[30 Ply 30U]

Jim, Who did you buy your 30-U from? 50mph is about the max you can expect to achieve. I can get up to 55mph in the right weather conditions. The carbs tend to be a little sensitive on the four cylinders. One day it will be smooth and run 50 all day, and with out touching anything, it will spit and sputter at 45mph the next day. Sometimes the idle is very smooth, and other days I have to throttle up at stop signs. You also have to drive it enough to keep fresh gas in the tank. In the spring I had some 6 month old Canadian purchased gas almost cost me a tow. I could not figure out what was going on, but sputtered into a fuel station and topped it off with fresh fuel and it ran like a top the rest of the day. 45mph is an ideal cruising speed.

[chetbrz]

The 30U should have a Spark Control cable that moves the distributor timing like the Vacuum advance in a modern car.? With the spark control fully extended into the start position, the distributor is turned to fire the cylinder just pasted TDC.? ?This is to ensure no kickback if you are hand cranking the engine.? ?Once the engine fires up the spark advance is pushed into the run position and should fire the cylinder a little before TDC.? ?I believe the setup procedure is in the owner?s manual.

Actually depending on the driving conditions you can screw with the Spark Control to obtain optimum driving efficiency.? If you can get 50 mph you are doing good and probably pushing the engine somewhat.? ?The 29/30U likes to cruise between 30 to 40 mph.? I believe ads boasted that the car could do 65mph but certainly not a sustainable driving speed with the stock 4.

See my OCR Reprint of timing instructions from the May 1929 Fifth Edition Plymouth Instruction Book:

http://www.chetscoins.com/1929/Work_Files/Ignition_Timing.htm

Chet?

[TodFitch]

Hmmm. There is a Jim Gray local to me with a P4. Any chance it is you?

For the 30-U here are the ignition specifications:

Breaker point gap 0.020"   
Cam Angle (Degrees) 52?
Set points to open at  0.050" piston travel before top dead center
Spark plugs 18 mm. metric   
Original Plugs AC C7
Spark Plug Gap 0.025"   

All that and more can be found on my 30-U specifications page at http://www.ply33.com/Models/30-U/specs.html

[p4jim]

I just purchased a 30U coupe with a round back window.? No serial number on the right door post.? Can I use a timing light on this engine?? What should the dwell be?? And the idle RPM??

It is now tuned by my ear which has never paid much attention to a 4-cylinder.? Last week it would not exceed 30mph but now has much better acceleration and reached 50mph (after distributor was advanced) but now does not like to idle after a quick stop.

I have purchased an owners manual but was too cheap to pay extra postage.?

Thanks for any help, jim gray