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

 

Marinus wrote:

...
So first impression all within spec.
...

I agree

Regards
Norbert

Hi Norbert,

Today i measured again:
Equus 590518: 35 degrees @idle, 34 degrees @3000 rpm 
Fluke:               36 degrees. @idle, 37 degress @3000 rpm 

1  tool measuring that the value is going down the other tool value is going up, why i have no clue.

Anyway for both tool measured data is within spec.


What about the small capacitor (kondensator) inside the distributor. I measured 190 nF (static measurement with the contact breaker disconnected). Could this part causing troubles? Also the primairy circuit showing factor 2 deviations in voltage between 2 spikes.?

Greetings in advance, Marc.
 

Hi Marc,

I do not trust your measuring equipment. I would go to someone with a real ignition oscilloscope as Christian uses during our workshops.

Hello Marc,
the capacitor looks new.... and new items are often reported as being of bad quality.
I can"t say anything about that. In 55 years of working on motorcycles, cars and other engines, I have never had to replace a capacitor because it was defective.

There are other causes of the differences in the ignition voltage possible besides the distributor, breaker, capacitor and the ignition coil.

Other possible reasons could be:
rotor, cap, cables, spark plugs. And differences in the compression and injection (rich / lean).

I think, you have to find out if the 'low voltages' are related to one or more cylinders or occur 'by chance'.

Regards
Norbert

Hi Norbert,

You were right about the capacitor. First I tried an old second capacitor (same problem) then a brand new one, namely the Bosch 1 237 330 310. This was an external capacitor of which I had to bend the metal bracket in some places to be able to attach it to the outside of my distributor. The problem was not solved. So it is now certainly NOT the capacitor.

However, I eventually found out that my new spark plug NGK BPR8EIX of cylinder 4 did not spark at the point but at the side. Note that I had found this spark plug type on the strich /8 website before I knew this forum. In Volker's table it says NGK BP6ES. Replaced cylinder 4 with an NGK BP6ES and the big fluctuation was immediately gone. Yippie.

Now there is a small fluctuation/jerking  that I actually also want to get rid of. This jerking  does not occur during a cold start (1100 rpm), however, when the speed drops below 1020 RPM, it starts to fluctuate. I also noticed that when I spray a little brake cleaner on the ZLS, the speed increases slightly. But I understand from chapter 9 that these valves are never 100% closed, so I assume for now that this is not a problem?

I have ordered a new coil and will let you know if that helps.

Kind regards, Marc

Hi Marc,

so what did you learn? Never trust another forum, just Jetronic.org !

Indeed....

Hi gentlemen the story goes on,

Today i removed the filter on the ZLS and i wanted to know how much the piston moves.

1) Any tips see the picture below. (and a picture from the WHB Book)



Thanks in advance.
Greetings Marc

 


 

Hi Marc,
the AAV (ZLS) doesn't close as it should do.

It has to be replaced or repaired...

Regards
Norbert

Thanks Norbert

Hi Marc,

as I showed during our workshop, it should be open around 3-5mm at room temperature and closed at 80°C.

Okay i got it.
Thanks a lot Volker.

Gr Marc

Story goes on at:
jetronic.org/de/forum/ignition/2488-w114...ventile-spiel-messen


Ps: I have also found a spare distributor, an older type, the PFUX6(R) 0 231 301 008. I will dismantle it and see what maintenance I can do on it.

1) Where can i find a detailed manual or sparepart list of ALL parts (or servcice parts)  of the PFUX6(R) 0 231 301 008 or the PFUX6(R) 0 231 301 015 

Thanks in advance
Greetings Marc

Hello everyone,

For the sake of completeness in this thread, here's a picture of my fully closed AAV (ZLS).
Unfortunately, this only happens on a hot summer day with the engine running stationary while the engine block temperature is 100 degrees Celsius. In other words, not good.

I'll try to clean it after the summer by vibrating it in an ultrasonic bath to see if it seals properly/close at 80 degrees Celsius.

Regards, Marc