Help- 1941 Plymouth Centrifugal Advance Question

[TerryB]

I’m try to help another forum member long distance and I need help with what I thought was a basic question.  With the engine stopped and the distributor cap off, can you check the operation of the distributor centrifugal advance on a 1941 Plymouth by twisting the rotor left or right?
 It was my belief the rotor should turn a small amount one way only and then snap back when released.  The car owner says his will not move when he attempts to twist it.  Any thoughts?

 

 

[Rusty_OToole]

You are right, sounds like the mechanism is frozen or maybe the springs broken. In any case the distributor needs attention. I would carefully turn the engine to TDC, photograph the distributor with the cap off and take out the distributor for repair or service. You want some record of the distributor's position so you can put it back in the same place.

Edited October 15, 2022 by Rusty_OToole (see edit history)

[TerryB]

17 minutes ago, Rusty_OToole said:

You are right, sounds like the mechanism is frozen or maybe the springs broken. In any case the distributor needs attention. I would carefully turn the engine to TDC, photograph the distributor with the cap off and take out the distributor for repair or service. You want some record of the distributor's position so you can put it back in the same place.

Thanks Rusty, the fellow has a spare distributor so I asked him to repeat the test on that one by just holding it in his hands. He says that rotor doesn’t move either.  So now I’m really scratching my head on what’s going on.

Edited October 15, 2022 by TerryB (see edit history)

[Bloo]

I would do exactly what @Rusty_OToole said, I would only add that I would take another pic after the breaker plate is out of the case. I wish it were as simple as twisting it and listening for a snap. The truth is that even grease that is slightly too heavy will impair and delay the motion. It probably is stuck, or at least all gummed up with old failed lubricant. It is time to tear it down, clean it all up, and lubricate it.

[LARRYCAROL]

I remember vw beetles having the same problem. We would remove vacuum advance, condenser & points then soak the distributor in can of atf overnight. Next day you clean it up and reinstall. 

[Rusty_OToole]

Can you find an auto electric shop with an old ignition analyser?  They can test the distributor in action after replacing worn parts and know exactly how the auto advance is working, how strong the spark is etc.

If you haven't seen this before, this is how they work.

 

 

Edited October 16, 2022 by Rusty_OToole (see edit history)

[halifaxhops]

They are great I have a few of them one for daily use and a few for backup.

[halifaxhops]

On 10/15/2022 at 7:12 PM, TerryB said:

Thanks Rusty, the fellow has a spare distributor so I asked him to repeat the test on that one by just holding it in his hands. He says that rotor doesn’t move either.  So now I’m really scratching my head on what’s going on.

If needed bring it over I am in Halifax, see what is going on with it.

[TerryB]

37 minutes ago, halifaxhops said:

If needed bring it over I am in Halifax, see what is going on with it.

Thanks, he’s near Pittsburgh. Appreciate the offer to help.

[halifaxhops]

Saw the Lancaster.

[TerryB]

Yes I’m doing long distance diagnosis, like those Click and Clack guys that used to be on the radio😀.

[halifaxhops]

Sounds like the advance cam is gummed up from the old grease.  Have him take it apart and clean it and use synthetic grease on the drive shaft the cam plate rides on.

[keithb7]

If the engine runs, using a timing light, as you rev up the engine watching the timing marks. Works well if you get a paint pen and mark 0 degrees, painting it white. Easier to see. As the engine revs up the timing mark will advance. Hold the throttle steady at a higher RPM, the timing should hold in the the advanced position. Proof if the mechanical advance is working or not. I assume the owner may have done this, and the timing is not advancing?  I agree with setting engine to #1 TDC. Pull the distributor and dig in.  You'll note there are two springs on the mechanical advance weights. They are not identical. One spring is lighter, less tension. It opens earlier at lower RPM. The other spring is thicker, more tension opening at a higher RPM. The fist time I saw the two different springs I thought someone has must have put in an incorrect spring, as they were not the same. I was wrong, they are supposed to be different.

 

 

Edited October 29, 2022 by keithb7 (see edit history)

[TerryB]

9 minutes ago, keithb7 said:

If the engine runs, using a timing light, as you rev up the engine watching the timing marks. Works well if you get a paint pen and mark 0 degrees, painting it white. Easier to see. As the engine revs up the timing mark will advance. Hold the throttle steady at a higher RPM, the timing should hold in the the advanced position. Proof if the mechanical advance is working or not. I assume the owner may have done this, and the timing is not advancing?  I agree with setting engine to #1 TDC. Pull the distributor and dig in.  You'll note there are two springs on the mechanical advance weights. They are not identical. One spring is lighter, less tension. It opens earlier at lower RPM. The other spring is thicker, more tension opening at a higher RPM. The fist time I saw the two different springs I thought someone has must have put in an incorrect spring, as they were not the same. I was wrong, they are supposed to be different.

 

 

Keith, we are working through this now.  Owner has never done service work and is learning everything as we go along.  As soon as we get basic TDC measurement understood, will advance😀to that test.

[keithb7]

Do you need assistance with basic TDC measurement and confirmation?

Edited October 29, 2022 by keithb7 (see edit history)

[TerryB]

22 minutes ago, keithb7 said:

Do you need assistance with basic TDC measurement and confirmation?

We are trying to get a clear understanding of TDC on the dampener pulley marks.  Engine was rebuilt and not sure the TDC mark on the pulley and real TDC still are one and the same.  There are also paint marks on the pulley to add to the confusion.

[Bloo]

I have been meaning to post a thread about how to do that, but unfortunately I don't have time to do it right now. Super short version:

 

1) Take all the plugs out, disconnect the battery

 

2) Make a fixed pointer adjacent to the harmonic balancer if there isn't one. Put it where you will be able to see it with the timing light easy. If there already is one, paint a line or paint its tip at 0 degrees, whatever is appropriate.

 

3) Get a giant plastic zip tie. Important: Long too. It's tail needs to be too long to get lost in a cylinder. Put it head first through the spark plug hole on number 1 cylinder. You might have to file on the zip tie a little to get it in. The spark plug holes are not over the piston in a flathead usually, so you are reaching over to the other side of the engine, all the way.

 

4) Crank the engine SLOWLY with a WRENCH. Hang on to your zip tie, and you should be able to feel it following the piston up the cylinder until the crank stops, with the head of the zip tie caught between the piston and the head, way over at the far side of the engine. Make a mark on the balancer that lines up with your pointer (or 0 if its a scale). Use a pencil or something else you can remove later.

 

5) Now crank the engine with the WRENCH backwards. Feel the zip tie follow the piston up again until it stops. Not much force. Don't unscrew the balancer bolt or anything, just hold it at the stopped point like you did before and make a second mark.

 

6) Make a mark in the center exactly between the 2 marks you just made. This is TDC. Red paint might be good.

 

7) Get rid of the two pencil marks, crank the piston back down with the WRENCH, pull the zip tie out and put everything back together.

 

 

Edited October 29, 2022 by Bloo (see edit history)

[ply33]

2 hours ago, Bloo said:

. . .

 

3) Get a giant plastic zip tie. Important: Long too. It's tail needs to be too long to get lost in a cylinder. Put it head first through the spark plug hole on number 1 cylinder. You might have to file on the zip tie a little to get it in. The spark plug holes are not over the piston in a flathead usually, so you are reaching over to the other side of the engine, all the way.

Many Chrysler product L-head engines, including the 1941 Plymouth, have a pipe threaded plug directly over the top of the #6 piston specifically for finding/measuring TDC.

[TerryB]

Just now, ply33 said:

Many Chrysler product L-head engines, including the 1941 Plymouth, have a pipe threaded plug directly over the top of the #6 piston specifically for finding/measuring TDC.

Yes, that is true for the Chrysler family flathead sixes.  It’s just a learning experience for a first time in to it person.  My friend Johnny is learning as he goes through this experience.

[Bloo]

16 minutes ago, ply33 said:

Many Chrysler product L-head engines, including the 1941 Plymouth, have a pipe threaded plug directly over the top of the #6 piston specifically for finding/measuring TDC.

That was nice of them, I wish more manufacturers were thinking ahead like that.

 

I do prefer the "stop" method (like the ziptie in my example above) because with the piston on the way up there is a lot of movement and there can be no doubt about where it stops. Right at the top, the piston comes to a stop and reverses, and it is still a little hard to tell exactly where TDC is.

 

With that hole over the piston though, you could still use the "stop" method with an immovable object screwed in the hole if you wanted to. That is how it is usually done on OHV engines using a spark plug hole.

 

Edited October 29, 2022 by Bloo (see edit history)

[keithb7]

I decided to put this together for my YT channel yesterday afternoon. The topic was worthy of a lesson for many: