Distributor cap wear

[Iantor]

Hi

I have recently developed an engine misfire on my 350i. I have changed plugs and leads (Plugs All looked perfect) and there was no improvement. I looked at the distributor and noticed 2 things
1/ The spring loaded contact where the coil attaches inside the cap was pusehes and worn completely flat (new dizzy cap arrived but not fitted)

2/ There appears to be excessive movement in the rotor arm (enough for almost 20 degrees) it does this from the shaft - not wear in the rotor arm)

The misfire only develops after 2-3 minutes and is quite severe - it sometimes goes away on a run. I have heard the the distributor can put upward pressure on the dizzy cap. Is there a way of checking it's seated before i fit the new cap and rotor arm.

Any help much appreciated

Ian

[Toltec]

Iantor said:

2/ There appears to be excessive movement in the rotor arm (enough for almost 20 degrees) it does this from the shaft - not wear in the rotor arm)

I think you will find you are just moving the mechanical advance around. Does the rotor arm spring back into position?

[Iantor]

No - it stays where you put it. Just rechecked it - though movement is probably not as much as 20 degrees. I can also pull the dizzy shaft up by about 8mm, no particular upward pressure, it just returns back down to the original position

Edited by Iantor on Tuesday 28th August 16:55

[Jack Valiant]

Sounds like you have the same problem as I had recently. Check that the circlip is still attached and that the bob wieghts and springs are attached. Suck in on the vacumn tube (before the in line valve) and make sure that the mechanism works on advance etc

Chris

[jmorgan]

Iantor said:

No - it stays where you put it. Just rechecked it - though movement is probably not as much as 20 degrees. I can also pull the dizzy shaft up by about 8mm, no particular upward pressure, it just returns back down to the original position

Edited by Iantor on Tuesday 28th August 16:55

Mine did that and the weights fell off. Not sure how you check for that.

[Iantor]

Checked the circlip, it's fine
Checked the vacuum advance, moves to & fro smoothly as you suck/ let go
Weights all seem fine
Just fitted the new dizzy cap with great difficulty, it was sitting too high - still no change, Starts up fine, idles perfectly and then as it warms up or after you blip the throttle, the misfire is back, bad as ever
Should add that at higher revs on a run the problems either disappears or diminishes, leads me to think timing is an issue

[Danny Hoffman]

try a new rotor arm (not from Intermotor!)

[Iantor]

I have a new rotor arm - just struggled to get the cap on with the new one - will try that tomorrow!!!!

[dwgriffith]

There are two rotor arms for the V8 distributors, one for the points type and the other for the electronic ones. The points type one sits higher on the shaft making the cap not fit without contacting the top of the arm thereby pushing the carbon rod right into the cap plastic. Alternatively, when the upper distributor shaft has come out of position because the plastic clip has not held, it will be sitting on top of the edges of the weights, it will be too high by the thickness of the weights? Out of position, the springs will have little effect on the shaft and this is probably what you have?

[Iantor]

Thanks - that sounds encouraging - I got the distributor cap and rotor arm from Rimmer Bros, I am sure I have the right Lucas cap but there was a guess made with the rotor arm (Although it looks identical to the old one). Shaft does look high but I cant see anything obviously wrong, think I may have to take to a garage, who could supply the right rotor arm (electronic ignition)

[dwgriffith]

The rotors look the same from the outside. If you look onto the mounting recess there will probably be a shoulder at the bottom, it's the height of this shoulder that makes most of the difference, check it against the old one.

[Iantor]

Will have a look later tonight, the running test was done with the old rotor arm