Recessed Rotor Button Syndrome

[ctaylor738]

Uhhh, just when you think you have seen it all.

From a 250SL with less than 100 miles on a new 123 distributor.  Complaint was hard starting and miss above 3000 rpm.

Cheers,

CT

[ja17]

Hello Chuck,

That's not so uncommon. The button can be broken off when the distributor cap is being "wrangled" in position. Be sure to go looking for the broken button. It will roll around in the distributor and can short out the ignition even after a new cap is installed. It can also jamb the centrifical advance mechanism.

[GGR]

I've seen that a couple of times. I always check it when I have the distributor cap off.

[wjsvb ✝︎]

Having been a marketer of ignition (and other auto) parts for the last 40 or so years, I can say that the problem is more common than it should be, particularly with aftermarket caps for Bosch applications.  It seems that there is a clinching operation in the assembly process which is often left incomplete, followed upon installation by...you guessed it!  Had to (still do) check each one.  Stretch the spring slightly to hold it in the tube. :'(  Once in the car, the contact button should be held in by the rotor contact/spring.  Jon

[ctaylor738]

Geez,

Guess I've been lucky and had a sheltered life.  It was a Bosch cap, though.

Cheers,

CT

[stickandrudderman]

On a slight tangent but there are aircraft engines that use Bosch rotors and there have been several incidents of rotor failure caused by poor quality of replacement parts.