051 Distributor Problems

[mrfatboy]

Hi all,

After getting my 280sl running nicely with a newly calibrated FIP I decided to replace the points, condenser, cap, and rotor.  No biggy right?  I have done it 10's of times since I owned the car.  Now the car runs terrible. Unfortunately, I replaced everything at once and don't know where exactly where the problem is.  I have spent hours and hours trying to get the dwell set correctly.  I tried gapping it to .3 -.4mm many times.  Every time I try I get different dwell numbers.  Could I have damaged something in the distributor when changing out the points?

I have a brand new set of spark plug wires that have been tested twice. New set of plugs.

With the new parts in place the engine runs rough for a minute than dies.  The plugs are getting fouled (I believe).  I went back to the old condenser and points to see if my new set was the problem.  The car starting running better but the dwell was 11.  The best I could do was get it to 22 and then started running poorly again. I gave up after that. 

I have never had this problem before and am unsure where to look or test for the problem. Does anybody have any ideas what might be going wrong?  What can I test for?

Did I fry both points?  Could the new condenser damage the points?  I don't really know what to ask.

I even tried two different dwell meters to make sure I was not getting faulty readings.

[twistedtree]

I had an issue where the new condenser wasn't making good ground contact against the distributor body.  Another possibility is that the screw that passes through the disti body and is connected to the points on the insider, and the condenser and coil on the outside, might be shorting out against the disti body.  It's also possible that the ground strap between the disti body and the plate that the points are on became dislodged or broke and you are not getting a good ground for the points frame.

If you disconnect the wire that goes between the points and the coil, you can then put an ohm meter between ground and the points side of the coil.  You then should see a very clear open circuit and short circuit when the points are opened and closed.  If it's flaky, then you have a ground/connection problem somewhere in there.

[Benz Dr.]

If you have a changing dwell angle this most often caused by wear inside the distributor. Top shaft, bottom shaft, point plate and other areas are usually the problem. Any dirt or oil on the point surface will cause a film that will create resistance.

[George Des]

I had this same problem with my original 051 many years ago. As Benz Dr says, it was wear within the distributor. In my case it was the plate and the points kept slipping out of adjustment. At the time, I replaced the whole distributor with a new one. It was one of the aluminum body ones. It worked well, but I've since replaced it with a rebuilt 051 and have no problems with it. I've found that the easiest way to gap the points is to pull the entire distributor out of the engine and gap the points on the bench. Just ensure the distributor goes back in oriented exactly the same way it came out. I can't remember if the drive key on the bottom of the shaft will prevent you from putting it back in 180 degrees out.

George

[Cees Klumper]

Now would be a good time to seriously consider getting a 123 distributor - eliminates distributor wear from the equation, switches you over to electronic ignition (no more points and better running characteristics) and cheaper than replacing (or rebuilding) the traditional distributor. Still, it should also be possible to fix the current setup of course.

[Benz Dr.]

How much is a 123 disributor?

[Cees Klumper]

I think they are between $300-400 but I may be off a bit. Here's a random page of a mechanic that comments on the system. You can program the desired advance curve on 'our' model:

http://www.mgcars.org.uk/peterburgess/123.html

[mbzse]

Here is another web page with some useful 123 Ignition info:
http://brits-n-pieces.com/shop/product_info.php/info/p6787_Distributor-123ignition-Mercedes-6-cylinder.html/XTCsid/e5fdd7a5d2642d6e344b56543c4ba08f
For you in the Americas, here is a web:
http://www.123ignitionusa.com/
/Hans in Sweden

.

[twistedtree]

I put a 123 in my '64 and so far so good.  If you are faced with any kind of a rebuild or replacement of your original distributor, I think the 123 is the way to go.

[ja17]

Hello,

If yours is the non-transistorized ignition, make sure that the threaded screw going through the distributor (wire from coil hooks to it) is not shorting out. It is supposed to have an insulator sleeve over it where it passes through the distributor. The sleeve deteriorates and a short can occur. Also make sure that forked end of the ignition points does not contact the breaker plate in the distributor or a short can occur. The electrical path from the coil all the way to the ignition contacts in the distributor must remain completely insulated or ignition spark will not occur or will be intermittent.

[mrfatboy]

I found the problem.  Twistedtree and JA were correct.  The bolt going through the distributor was touching the distributor casing and shorting out.  There was not a plastic insulating sleeve in there.  I don't remember ever seeing one there either.  It must have dissolved like Joe said and I got lucky all these years by having the bolt perfectly in the center of the pass through hole.   I was able to insulate the bold with some black electrical tape and I also had some clear plastic (3/8" I believe) tubing which I cut about an 1/8" off and made a grommet for the hole.

Thanks for everybody's help.

[Benz Dr.]

I've seen the odd distributor with this insulating sleeve but I don't think it's an actual part of the original unit. My mid 60's Bosch dealers book doesn't show this part.
If you have the two insulating discs on each side of the hole they will center the screw and it should never touch the housing.

[mrfatboy]

I do have the two insulating discs.  Maybe the one on the inside was not properly in place allowing the screw to touch the dist casing

[Benz Dr.]

The two insulating discs are not the same size or thickness. The smaller outside one should fit neatly into the area that is milled to accept this part. The inside one is thinner so it can bend slightly to the shape of the casting.

[m300cab]

May also be the wire that goes from distributor to resistor, you may have a kink
replace all those wires!