Jerking (ruckeln?) W114 250 CE caused by distributor radial play?

Hi All,

My 114.980 engine is not standing still at idle speed. I fail for the coin test: I can not put a coin on it like you sometimes see people doing and the coin is not rolling away. 
When i stand in front of my car the engine block moves/shakes from left to right and vice versa i believe this is called jerking.

I put new stuff in like, spark plugs, cables, distributor rotor and cap.
I checked my coil resistance (primary and secundary) and even used a spare coil. I checked breaker contacts and measured the capacitor in the distributor. Both seems okay. I used a occiloscoop with a Hantek HT25 probe to see the sparks coming by directly out of the coil. The result is that between 2 sparks the Voltage can be doubled, see pic 1.
I checked the radial play: at start 0.0 mm and at gentle push 0.1 mm, see pic 2.  
Although i measured not directly at cam height (but at rotor height) my first estimate is that this play can cause an extra or smaller opening of the distributor contact of 0.15 mm (transmission ratio from cam to breaker points approx 1.5)

1) could this be the reason for my engine jerking?
2) what is the specification for maximum radial play
3) any other tips?

Happy to hear from anybody.

Greetings Marc

 

 

 

Hi Marc,
the radial play is much too high - as I understand, from one side to the other 0,2 mm.

You will have a dwell that's running out of all specs at changing revs.
Did you measure the dwell?

Your distributor has to be replaced or revisioned...

Is your car an early model without transistorised ignition?

Regards
Norbert

Hi,

I fully agree to Norbert's analysis.

Hi Norbert,


No it is +- 0,05 mm. From one side 0.0 mm to the other side it was 0.1 mm.
Does this change your view?

Will check the dwell angle at different revolutions

And yes i have no transistor ignition (was planning to install it after the engine is running smooth again).

Gr Marc

Hello Marc,
of course that makes a difference ... but the play is still considerable and you cannot ignore it.
You have the problem with different levels of ignition voltage.

I did not find any data about the permitted play - a new distributor is without a noticeable play.
I asked for the dwell. I am quite sure it will run out of the limits  with changing revs.

As so often, it is not certain that the exchange of the part fixes the error. But you can only determine by fixing this problem whether the error is gone then.

Regards
Norbert

edit: My car is a straight six with conventional ignition, too.
I once had problems with an instable idle.
The breaker looked like this one (I think, the 'hill' higher than here in the photo):

After removing the 'hill' the idle was stable.

Hi Norbert,

Just did a first quick test with my new Equus 590518 tool. 
At Idle the dwell angle is 35 degrees
At 3000 rpm the angle is 36 degrees
But i will do this again with my fluke automotive meter hopefully tomorrow.

Checked the values in the VdH flipbooks: At Idle 34-41 degrees. At 3000 rpm it should be within +- 3 degrees from measured value at idle.
So first impression all within spec.

I cleaned my breaker contacts with wetted paper with breakcleaner. I did not see any "hill". 

Keep you posted.

Greetings Marc