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unstable spark timing


Egbert

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Hello fellow flathead drivers,

Since a year i have a Plymouth 1937 Coup P4 with Autolite distributor.
I have a annoying problem with the ignition timing, the markings are ´dancing´ back and forth as if the advancer is loose.
But i have rebuild the distributor, mechanical advancer and vacuum advancer.
Today i found out the end of the driveshaft has a lot of clearance in the engine block.
It makes a difference of about 6 degrees on the cam.
This would explain the dancing of the marking under the strobelight.
Is the end of the shaft supposed to be snug in the drive part in the block ?
(Seems logical to me)
Does anyone ever experienced this problem ?

Greetings from Amsterdam.

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Many years ago I had a dual point distributor in my 413 that had a problem with the timing dancing around.  The bushings inside the distributor were worn allowing the shaft to wobble about.  When you rebuilt the distributor did you replace those bushings or check the side play of the shaft in the housing?

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Thanks for the reply, i did check the bushings and there was hardly any sideplay at the shaft.
I will keep it in mind but for now i distrust the backlash between the drive part in the block and the distributor shaft.
There is not supposed to be any play between the drive part and the shaft i suppose ?

Edited by Egbert
bad discription
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there will always be some clearance between the two, otherwise the drive tang wouldn't slide in, you'd have to press it in.  It's not a high load connection so I don't really see it wearing, but I do not think there is a specification for the clearance either.  I also wonder how you are seeing this play?  If you are turning the rotor by hand then what you are seeing is the advance plate in operation, not the slop between the oil pump and distributor drive connection. 

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when i have the distributor in my hand there is no slop between the cam and the shaft, it takes some force to overcome the spring tension of the mechanical advancer.
When the distributor is in the block i can very easily rotate it and feel the slop. (without the advancer moving)
So the distributor shaft presses in the oil pump shaft and the oil pump shaft is driven by a gear by the camshaft.

it seems unlikely but it feels like there´s play directly at the end of the shaft.
Otherwise i guess there could only be play between the oil pump gear and the camshaft.
Is it common for the oil pump gear to wear out ?
I guess i have to pull the oil pump, do i am not to keen on doing that.

Would there be a alternative to check backlash ?

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Well, I would probably pull the oil pan and observe the movement of the distributor drive in the oil pump gear as well as the play between the oil pump gear and the camshaft gear.  That's the only way I can think of to know exactly what is going on, but not a fun job either. 

 

My thinking is that in use any clearances would be taken up in rotation and shouldn't be an issue.  None of those clearances are tight even when new.  I would be rechecking the distributor before I pulled the pan. 

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Are you sure that the breaker plate is fully tight inthe body of the distributor housing. Or the breaker plate assembly might be worn out and you are getting slop from this area.  I have a friend and alsong with me we both have 39 Desoto.s  He drove up to my house for a car show and noticed the engine was not running smooth.  We took the dizzy cap off and found that the  two halved of the breaker plate were loos with each other there was a lot of slop.  We chnaged out the old one with a NOS breaker plate and that solved the issue.  The breaker plate is held in position with two screws.

 

Also the Dod/Ply distributor shaft is shorted than onthe Chryler/Desoto distrbutor shaft.  Do you have the correct dizzy. Is there any possibility that you mifht have the incorrect dizzy installed.  Tellme the IG number on the red tag that is mounted onthe outside of the body.

According to my Motors repair manual the correct dizzy number is autolite   IGS-4003B-1  which was used on 1936-38 plymouths  also on the 36 Plymouth was the IGS-4003A-1

Rich Hartung

desoto1939@aol.com

Edited by desoto1939
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Do you know anyone with a car similar to yours with whom you could trade distributers for a bit to see if it's in the distributor or the oil pump?  Most are interchangeable within the engine series as in 23 inch long heads will pretty much swap with any 36 and later cars and trucks with 23 inch blocks The 23 to 25.5 inch engines do not interchange distributors.

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Thanks for the replys Rich & Greg; i just noticed them.
The  breaker plate seems tight, the axle has a bit of slack in the housing;
I just got a vacuum pot from the specialist from Boston (don´t know if it´s okay to use names) I will test if my own repaired
vacuum pot was at fault.
I´m also expecting bushes so i will change them to be sure (plugs and wires are already done)
It is the the IGS-4003B-1 so that´s good news.

Here in the Netherlands there ain´t many 23 Mopar flatheads and none that i know.
It´s hard to find a experienced garage and even harder to get parts.
But i get a lot of curious looks and smiling faces ?
I will keep an update if there is news, again thanks for thinking along.
Keep Sailing Along...


 

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10 hours ago, ptwothree said:

A worn timing chain will cause timing to fluctuate as well.

 

If you can find a scope, you can put the spark impulses in a stack and watch to see if they vary.

When you raise the throttle they will line up....that's the sign of a worn timing chain.

At idle the chain is sloppy, when you rev the engine it tightens.

You can time the engine at 3,000 rpm very nicely, because the timing mark won't be bobbing around.

That takes a timing light that has an advance feature. Figure out the mechanical advance in the distributor then dial it into the timing light. Then time the engine at the full advance rpm using the idle mark.

The car will run well at highway speed, but at idle not so much.

A sloppy timing chain of course causes the ignition timing and the valve timing to be off as well.

When you change the chain it's best to change both sprockets too otherwise the chain won't last long.

When you go to change the crank sprocket cut a piece of pipe to fit over the crankshaft with a cap on it.

Heat the gear good and hot with a propane torch before you try to slip it on.

Have the pipe ready with a  big hammer to help it into place.

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1 hour ago, Tooljunkie said:

Saw a guy flip a battery upside down to boost a dead one, yup it leaked. 

 

Back in the days when I was a dealer mechanic, we were told that to warrantee a battery we had to certify that we had done the following:

1) turn the battery over 360 degrees.

2) charge the battery 1 hour on 40 amp setting.

3) load test it on a load tester or crank the engine with ignition coil disconnected for 30 seconds without the voltage dropping below 10.5 while cranking.

if it failed #3 after 1 & 2 then you replaced it.

The idea being that sediment could cause the battery to go dead. By rolling it over the sediment would fall into the containment area beneath the plates.

These were new cars under warrantee with original batteries. I am not sure I would follow this procedure for my own stuff, but I did like getting paid for my work so I did as they asked.

 

Flipping a battery to touch the terminals together is an act worthy of a Darwin Award!

That person obviously has never been in a shop when a battery EXPLODED.

Some brands were noted for exploding when you cranked the engine and the mechanics routinely covered them while working on the car.

Peugeot OEM "Battery Rose" were prone to exploding. We used to joke they never failed or wore out because they exploded first!

You never set tools anywhere near a battery which could fall on it without first putting a rag over it. All it takes is a spark and CABOOM!

Once a friend of mine was using a die grinder under the hood of a car. I told him to cover the battery and he told me where I could go. I turned my back and CABOOM! I would have said "I told you so!" But he couldn't hear for a while and needed to use the shower fast so I got out of his way.

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Lol, some of the crazy things you see.  Not so long ago I went thru battery safety training with my son.  Always unhook the grounded side first, explained to him why.  I like to know why I am doing what i am doing so when I go over things with him I explain why we do it that way.   

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even when you do things the right way, things can go wrong.  Many years ago I was giving a guy a jump from my 61Valiant.  Brand new battery too.  Put the jumper cables on without the car running, ground last.  Got in the Valiant to start it.  First clank of the little gear drive starter engaging and BOOM, top of the battery blew off!.

 

 

 

Took a week to get the acid washed off and fully neutralized.

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